JP7237221B2 - lithium ion secondary battery - Google Patents

Description

One aspect of the present invention relates to an article, method, or manufacturing method. Alternatively, the invention relates to a process, machine, manufacture, or composition of matter. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof. In particular, the present invention relates to a positive electrode active material that can be used for a secondary battery, a secondary battery, and an electronic device having the secondary battery.

Note that in this specification, a power storage device generally refers to elements and devices having a power storage function. For example, storage batteries such as lithium ion secondary batteries (also referred to as secondary batteries), lithium ion capacitors, electric double layer capacitors, and the like are included.

In this specification, electronic equipment refers to all devices having a power storage device, and electro-optical devices having a power storage device, information terminal devices having a power storage device, and the like are all electronic devices.

In recent years, various power storage devices such as lithium ion secondary batteries, lithium ion capacitors, and air batteries have been actively developed. In particular, lithium-ion secondary batteries, which have high output and high energy density, are used in portable information terminals such as mobile phones, smart phones, tablets, or notebook computers, portable music players, digital cameras, medical equipment, or hybrid vehicles (HEV). , electric vehicles (EV), and next-generation clean energy vehicles such as plug-in hybrid vehicles (PHEV). It has become an indispensable part of the modernized society.

Characteristics required for lithium-ion secondary batteries include further increase in energy density, improvement in cycle characteristics, safety in various operating environments, and improvement in long-term reliability.

Therefore, improvements in positive electrode active materials have been investigated with the aim of improving the cycle characteristics and increasing the capacity of lithium ion secondary batteries (Patent Documents 1 and 2). In addition, studies on the crystal structure of positive electrode active materials have also been conducted (Non-Patent Documents 1 to 3).

Japanese Patent Application Laid-Open No. 2002-216760 JP 2006-261132 A

Ｔｏｙｏｋｉ Ｏｋｕｍｕｒａ ｅｔ ａｌ，”Ｃｏｒｒｅｌａｔｉｏｎ ｏｆ ｌｉｔｈｉｕｍ ｉｏｎ ｄｉｓｔｒｉｂｕｔｉｏｎ ａｎｄ Ｘ－ｒａｙ ａｂｓｏｒｐｔｉｏｎ ｎｅａｒ－ｅｄｇｅ ｓｔｒｕｃｔｕｒｅ ｉｎ ０３－ａｎｄ ０２・ｌｉｔｈｉｕｍ ｃｏｂａｌｔ ｏｘｉｄｅｓ ｆｒｏｍ ｆｉｒｓｔ－ｐｒｉｎｃｉｐｌｅ ｃａｌｃｕｌａｔｉｏｎ”， Ｊｏｕｒｎａｌ ｏｆ Ｍａｔｅｒｉａｌｓ Ｃｈｅｍｉｓｔｒｙ， ２０１２， ２２， ｐ． 17340-17348 Motohashi, T.; et al, "Electronic phase diagram of the layered cobalt oxide system LixCoO2 (0.0≤x≤1.0)", Physical Review B, 80(16); 165114 Zhaohui Chen et al, “Staging Phase Transitions in LixCoO2, Journal of The Electrochemical Society, 2002, 149(12) A1604-A1609 W. E. Counts et al, Journal of the American Ceramic Society, (1953) 36[1] 12-17. Fig. 01471

An object of one embodiment of the present invention is to provide a positive electrode active material for a lithium-ion secondary battery, which has high capacity and excellent charge-discharge cycle characteristics, and a method for manufacturing the same. Another object is to provide a method for manufacturing a positive electrode active material with high productivity. Alternatively, one aspect of the present invention is
An object is to provide a positive electrode active material which is used for a lithium-ion secondary battery so as to suppress a decrease in capacity during charge-discharge cycles. Another object of one embodiment of the present invention is to provide a high-capacity secondary battery. An object of one embodiment of the present invention is to provide a secondary battery with excellent charge-discharge characteristics. Another object of one embodiment of the present invention is to provide a secondary battery with high safety or reliability.

Another object of one embodiment of the present invention is to provide a novel substance, active material particles, a power storage device, or a manufacturing method thereof.

The description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. In addition, specifications, drawings,
Problems other than these can be extracted from the description of the claims.

One embodiment of the present invention is a secondary battery including a positive electrode including a positive electrode active material and metallic lithium in a negative electrode, wherein the positive electrode active material includes lithium, nickel, manganese, cobalt, oxygen, magnesium, and fluorine, and manganese has an atomic ratio of 0.5 to 2 times that of nickel, and the secondary battery is charged at a constant current in a 25 ° C. environment until the battery voltage reaches 4.6 V, and then the current value After constant voltage charging until 0.01 C, when the positive electrode was analyzed by powder X-ray diffraction using CuKα1 line, one or more peaks were observed in the range of 2θ larger than 17.5 ° and smaller than 20 °. is greater than 36 ° and less than 38.5 °, one or more peaks are observed in the range of 2θ is greater than 43.5 ° and less than 46.5 °, powder X-ray of the positive electrode When the diffraction pattern was analyzed by the Rietveld method, the positive electrode had a first crystal phase and a second crystal phase, and the first crystal phase and the second crystal phase belonged to the space group R-3m. In the first crystal phase, the lattice constant of the a-axis is a
1, the c-axis lattice constant is c1, and in the second crystal phase, the a-axis lattice constant is a2, the c-axis lattice constant is c2, and the average value of a1/c1 and a2/c2 is from 0.198. large 0.20
2, it is a secondary battery.

Alternatively, one embodiment of the present invention is a secondary battery including a positive electrode including a positive electrode active material and metal lithium in a negative electrode, wherein the positive electrode active material includes lithium, nickel, manganese, cobalt, oxygen, magnesium, and fluorine. , The atomic ratio of manganese has a region of 0.5 to 2 times that of nickel, and the secondary battery is discharged at a constant current in an environment of 25 ° C. until the battery voltage reaches 2.5 V, When the positive electrode is analyzed by powder X-ray diffraction using CuKα1 rays, the positive electrode has a third crystal phase represented by the space group R-3m, and in the third crystal phase, the lattice constant of the a-axis is a3
, the c-axis lattice constant is c3, and the average value of a1/c1 and a2/c2 is 0 of a3/c3
. It is a secondary battery that is larger than 993 times and smaller than 1.02 times.

Alternatively, one embodiment of the present invention includes the positive electrode described above and a negative electrode, wherein the negative electrode comprises graphite,
A secondary battery containing at least one of graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, and carbon black,
The negative electrode is a secondary battery comprising at least one of carbon, silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium.

Alternatively, one embodiment of the present invention includes the positive electrode described above and a negative electrode, wherein the negative electrode contains carbon,
silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth,
A secondary battery containing at least one of silver, zinc, cadmium, and indium.

Alternatively, in one embodiment of the present invention, lithium, nickel, manganese, magnesium,
A method for producing a positive electrode active material containing oxygen and fluorine, wherein the positive electrode active material is produced through a heating step of heating a first mixture and a second mixture, and the first mixture is Lithium fluoride is used as the lithium source and the fluorine source, magnesium fluoride is used as the fluorine source and the magnesium source, and the molar ratio of the lithium fluoride and the magnesium fluoride is lithium fluoride:magnesium fluoride=x:1 ( 0.1 ≤ x ≤ 0.5), and the second mixture contains nickel and manganese that is 0.5 to 2 times the amount of nickel contained in the second mixture,
The temperature of the heating step is 600° C. or higher and 950° C. or lower in the manufacturing method of the positive electrode active material.

According to one embodiment of the present invention, it is possible to provide a positive electrode active material for a lithium-ion secondary battery that has high capacity and excellent charge-discharge cycle characteristics, and a method for manufacturing the same. In addition, a method for manufacturing a positive electrode active material with high productivity can be provided. Further, by using it in a lithium ion secondary battery, it is possible to provide a positive electrode active material that suppresses a decrease in capacity during charging and discharging cycles. In addition, a high-capacity secondary battery can be provided. In addition, a secondary battery with excellent charge/discharge characteristics can be provided. Moreover, a secondary battery with high safety or reliability can be provided. In addition, novel substances, active material particles, power storage devices, and manufacturing methods thereof can be provided.

4A and 4B illustrate an example of a method for manufacturing a positive electrode active material of one embodiment of the present invention; 4A and 4B are diagrams showing the crystal structure of a positive electrode active material of one embodiment of the present invention; 4A and 4B are diagrams showing the crystal structure of a positive electrode active material of one embodiment of the present invention; FIG. 4 is a cross-sectional view of an active material layer in the case of using a graphene compound as a conductive aid; 4A and 4B are diagrams for explaining a charging method of a secondary battery; FIG. 4A and 4B are diagrams for explaining a charging method of a secondary battery; FIG. 4A and 4B are diagrams for explaining a method of discharging a secondary battery; FIG. 4A and 4B illustrate a coin-type secondary battery; FIG. 3 is a diagram for explaining a cylindrical secondary battery; 4A and 4B illustrate an example of a secondary battery; 4A and 4B illustrate an example of a secondary battery; 4A and 4B illustrate an example of a secondary battery; 4A and 4B illustrate an example of a secondary battery; 4A and 4B are diagrams for explaining a laminated secondary battery; 4A and 4B are diagrams for explaining a laminated secondary battery; The figure which shows the external appearance of a secondary battery. The figure which shows the external appearance of a secondary battery. 4A and 4B are diagrams for explaining a method for manufacturing a secondary battery; FIG. 4 is a diagram for explaining a bendable secondary battery; FIG. 4 is a diagram for explaining a bendable secondary battery; 1A and 1B are diagrams each illustrating an example of an electronic device; 1A and 1B are diagrams each illustrating an example of an electronic device; 1A and 1B are diagrams each illustrating an example of an electronic device; 1A and 1B are diagrams each illustrating an example of an electronic device; Measurement results by XRD. Measurement results by XRD. Measurement results by XRD. Charge/discharge characteristics of secondary batteries. Cycle characteristics of secondary batteries.

Embodiments of the present invention will be described in detail below with reference to the drawings. However, those skilled in the art will easily understand that the present invention is not limited to the following description, and that the forms and details thereof can be variously changed. Moreover, the present invention should not be construed as being limited to the description of the embodiments shown below.

In this specification and the like, crystal planes and directions are indicated by Miller indexes. Crystallographic planes and orientations are indicated by adding a superscript bar to the number from the standpoint of crystallography. symbol) may be attached. In addition, individual orientations that indicate directions within the crystal are indicated by [ ], collective orientations that indicate all equivalent directions are indicated by <>, individual planes that indicate crystal planes are indicated by ( ), and aggregated planes that have equivalent symmetry are indicated by { }. to express each. 1 Å is 10 ⁻¹⁰ m.

In this specification and the like, segregation refers to a phenomenon in which an element (eg, B) is spatially nonuniformly distributed in a solid composed of a plurality of elements (eg, A, B, and C).

In this specification and the like, the surface layer portion of a particle such as an active material refers to a region from the surface to about 10 nm. A surface caused by a crack or crack can also be called a surface. A region deeper than the surface layer is called the inside.

In this specification and the like, the layered rock salt type crystal structure of a composite oxide containing lithium and a transition metal has a rock salt type ion arrangement in which cations and anions are alternately arranged, and the transition metal and lithium are A crystal structure in which lithium can diffuse two-dimensionally because it is regularly arranged to form a two-dimensional plane. In addition, there may be defects such as lack of cations or anions. again,
Strictly speaking, the layered rock salt type crystal structure may be a structure in which the lattice of the rock salt type crystal is distorted.

In this specification and the like, a rock salt crystal structure refers to a structure in which cations and anions are alternately arranged. In addition, there may be a lack of cations or anions.

Layered rock salt crystals and anions of rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that anions in pseudospinel-type crystals also have a cubic close-packed structure. When they meet, there are crystal planes that align the cubic close-packed structure composed of anions. However, the space group of layered rocksalt crystals and pseudospinel crystals is R-3m, and the space group of rocksalt crystals is Fm-3m (the space group of general rocksalt crystals) and Fd-3m (the simplest symmetry). Therefore, the Miller indices of the crystal planes satisfying the above conditions are different between the layered rocksalt crystals and the pseudospinel crystals and the rocksalt crystals. In this specification, when the direction of the cubic close-packed structure composed of anions is aligned in the layered rocksalt crystal, the pseudospinel crystal, and the rocksalt crystal, it is sometimes said that the orientation of the crystals is approximately the same. be.

TEM (transmission electron microscope) image, STE
It can be determined from an M (scanning transmission electron microscope) image, a HAADF-STEM (high angle scattering annular dark field scanning transmission electron microscope) image, an ABF-STEM (annular bright field scanning transmission electron microscope) image, or the like. X-ray diffraction (XRD), electron beam diffraction, neutron beam diffraction, etc. can also be used as a basis for determination. In a TEM image or the like, the arrangement of cations and anions can be observed as repetition of bright lines and dark lines. When the direction of the cubic close-packed structure in the layered rock salt crystal and the rock salt crystal is aligned, the angle formed by the repetition of the bright line and the dark line between the crystals is 5 degrees or less, more preferably 2.5 degrees or less. Observable. In some cases, light elements such as oxygen and fluorine cannot be clearly observed in a TEM image or the like, but in such cases, it is possible to determine whether the orientations match with the arrangement of the metal elements.

In this specification and the like, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the lithium that can be inserted and detached included in the positive electrode active material is desorbed. For example, the theoretical capacity of _LiCoO2 is 2
74 mAh/g, the theoretical capacity of LiNiO ₂ is 274 mAh/g, and the theoretical capacity of LiMn ₂ O ₄ is 148 mAh/g.

In this specification and the like, the charge depth is 0 when all the lithium that can be inserted and detached is inserted, and the charge depth is 1 when all the lithium that can be inserted and detached in the positive electrode active material is desorbed.
It is assumed that

In this specification and the like, charging means moving lithium ions from the positive electrode to the negative electrode in the battery and moving electrons from the negative electrode to the positive electrode in an external circuit. As for the positive electrode active material, releasing lithium ions is called charging. A positive electrode active material with a charge depth of 0.8 or more is referred to as a positive electrode active material charged at a high voltage. So for example Li
If it is charged to 219.2 mAh/g or more in CoO ₂ , it is a positive electrode active material charged at a high voltage. In LiCoO ₂ , under an environment of 25° C., the positive electrode active material after constant-current charging until the battery voltage reaches 4.6 V (in the case of counter electrode lithium) and then constant-voltage charging until the current value reaches 0.01 C is also a positive electrode active material charged at a high voltage.

Similarly, discharging refers to the transfer of lithium ions from the negative electrode to the positive electrode within the battery and the transfer of electrons from the positive electrode to the negative electrode in an external circuit. As for the positive electrode active material, the insertion of lithium ions is called discharging. In addition, a positive electrode active material with a charge depth of 0.06 or less, or a positive electrode active material that has been discharged to a capacity of 90% or more of the charged capacity from a state charged at a high voltage is referred to as a fully discharged positive electrode active material. . For example, if LiCoO ₂ has a charge capacity of 219.2 mAh/g, it is in a state of being charged at a high voltage.
The positive electrode active material after discharging at 197.3 mAh/g or more is a fully discharged positive electrode active material. In LiCoO ₂ , the positive electrode active material after constant current discharge until the battery voltage becomes 3 V or less (in the case of counter electrode lithium) under an environment of 25° C. is also regarded as a sufficiently discharged positive electrode active material.

Particle size can be evaluated, for example, by a laser scattering method. Alternatively, the surface of the particles can be observed and evaluated by SEM (scanning electron microscope) in some cases. Alternatively, it may be possible to observe and evaluate the cross section of the particles by SEM, TEM, or the like.

(Embodiment 1)
[Method for preparing positive electrode active material]
First, an example of a method for manufacturing the positive electrode active material 100 which is one embodiment of the present invention is described with reference to FIGS.

<S11>
As shown in S11 of FIG. 1, first, a halogen source such as fluorine and a magnesium source are prepared as materials for the first mixture. A lithium source is also preferably provided.

As the fluorine source, for example, lithium fluoride, magnesium fluoride, or the like can be used. Among them, lithium fluoride is preferable because it has a relatively low melting point of 848° C. and is easily melted in the annealing step to be described later. Examples of chlorine sources that can be used include lithium chloride and magnesium chloride. Examples of magnesium sources that can be used include magnesium fluoride, magnesium oxide, magnesium hydroxide, and magnesium carbonate. As the lithium source, for example, lithium fluoride and lithium carbonate can be used. That is, lithium fluoride can be used both as a lithium source and as a fluorine source. Moreover, magnesium fluoride can be used as both a fluorine source and a magnesium source.

For example, lithium fluoride is prepared _as a fluorine source and a lithium source _, and magnesium fluoride is prepared as a fluorine source and a magnesium source. The effect of lowering the melting point is maximized when mixed at a ratio of about 10% (Non-Patent Document 4). On the other hand, if the amount of lithium fluoride increases, there is a concern that the amount of lithium becomes excessive and the cycle characteristics deteriorate. Therefore, lithium fluoride Li
The molar ratio of F to magnesium fluoride MgF ₂ is LiF:MgF ₂ =x:1 (0≤x≤1.
9), more preferably LiF: _MgF2 =x:1 (0.1≤x≤0.5), still more preferably about LiF: _MgF2 =0.33:1.

Also, a solvent is prepared when the subsequent mixing and pulverization steps are performed in a wet manner. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), and the like. It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment mode, acetone is used.

<S12>
Next, the materials of the first mixture are mixed and pulverized (S12). Mixing can be dry or wet, but wet is preferred because it allows for smaller comminutes. For example, a ball mill, bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use, for example, zirconia balls as media. It is preferred that the mixing and grinding steps are sufficiently performed to pulverize the first mixture.

<S13, S14>
The materials mixed and pulverized as described above are recovered (S13) to obtain a first mixture (S14).

The first mixture preferably has an average particle size (D50) of, for example, 600 nm or more and 20 μm or less. If the first mixture has been pulverized in this way, when it is mixed with a composite oxide containing lithium, transition metals and oxygen in a later step, the first mixture is evenly spread on the surfaces of the particles of the composite oxide. Easy to attach. When the first mixture is uniformly adhered to the composite oxide particles, the halogen and magnesium can be distributed throughout the surface layer of the composite oxide particles after heating, which is preferable. The average particle size of the first mixture is, for example, 0.2 times or more and 5 times or less the average particle size of the composite oxide obtained in S25 described later, or more than 0.2 times and 0.
. 8 times smaller.

<S21>
Next, as shown in S21 of FIG. 1, a lithium source and a transition metal source are prepared as materials for a composite oxide containing lithium, transition metal and oxygen.

As the lithium source, for example, lithium carbonate, lithium fluoride, or the like can be used.

At least one of cobalt, manganese, and nickel can be used as the transition metal. Since the oxide containing lithium, transition metal and oxygen preferably has a layered rock salt type crystal structure, the mixing ratio of cobalt, manganese, and nickel that can form a layered rock salt type is preferred. In addition, aluminum may be added to these transition metals to the extent that a layered rock salt type crystal structure can be obtained.

By using the positive electrode active material of one embodiment of the present invention, the secondary battery can be charged or discharged at high current density. By using nickel as a transition metal, for example, the capacity of a secondary battery can be increased. Also, by using nickel as a transition metal, for example, the charging voltage can be lowered in some cases. By reducing the charging voltage, decomposition of the electrolyte solution can be suppressed in the case where the positive electrode active material of one embodiment of the present invention is used in the secondary battery. Also, by using nickel as the transition metal, for example, the cost of the secondary battery can be reduced.

By using manganese as a transition metal, for example, the safety of secondary batteries can be enhanced. In addition, by using manganese as a transition metal, for example, it is possible to suppress a decrease in capacity that accompanies charge-discharge cycles. Moreover, by using manganese as the transition metal, for example, the cost of the secondary battery can be further reduced. Further, by using manganese as a transition metal, for example, it may be possible to suppress structural changes in the composite oxide during charging and discharging.

It is also preferred to have nickel and manganese as transition metals. By using nickel and manganese as transition metals, for example, a more stable secondary battery with high capacity and little structural change during charging and discharging can be realized.

As the transition metal source, oxides, hydroxides, and the like of the above transition metals can be used. As the cobalt source, for example, cobalt oxide, cobalt hydroxide, or the like can be used. Manganese oxide, manganese hydroxide, or the like can be used as the manganese source. As a nickel source, nickel oxide, nickel hydroxide, or the like can be used. As an aluminum source, aluminum hydroxide, aluminum oxide, or the like can be used.

<S22>
Next, the above lithium source and transition metal source are mixed (S22). Mixing can be dry or wet. For example, a ball mill, bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use, for example, zirconia balls as media.

<S23>
Next, the above mixed materials are heated. This step may be referred to as firing or first heating in order to distinguish it from the subsequent heating step. Heating is preferably carried out at 800°C or higher and lower than 1100°C, more preferably 900°C or higher and 1000°C or lower, and even more preferably about 950°C. Too low a temperature may result in insufficient decomposition and melting of the starting material. On the other hand, if the temperature is too high, defects may occur due to excessive reduction of the transition metal or evaporation of lithium. For example, defects can occur in which cobalt becomes divalent.

The heating time is preferably 2 hours or more and 20 hours or less. Firing is preferably carried out in an atmosphere containing little water such as dry air (for example, a dew point of −50° C. or less, more preferably 100° C. or less). For example, heating is performed at 1000° C. for 10 hours, the temperature is preferably raised at 200° C./h, and the flow rate of the drying atmosphere is preferably 10 L/min. The heated material is then cooled to room temperature. For example, it is preferable that the cooling time from the specified temperature to room temperature is 10 hours or more and 50 hours or less.

<S24, S25>
The materials fired above are collected (S24) to obtain a composite oxide containing lithium, transition metals and oxygen (S25). Specifically, lithium cobaltate, lithium manganate, lithium nickelate, lithium cobaltate in which cobalt is partially substituted with manganese, or nickel-manganese-lithium cobaltate is obtained.

Alternatively, a composite oxide containing lithium, a transition metal, and oxygen synthesized in advance may be used as S25. In this case, S21 to S24 can be omitted.

When using a composite oxide containing lithium, a transition metal, and oxygen synthesized in advance, it is preferable to use one containing few impurities. Here, the main components are lithium, transition metals (cobalt, nickel, manganese), aluminum, and oxygen, and the elements of the main components are impurities. For example, when analyzed by glow discharge mass spectrometry, the total concentration of elements other than lithium, transition metals and oxygen is preferably 10,000 ppm wt or less, more preferably 5000 ppm wt or less. In particular, the total impurity concentration of transition metals such as titanium and arsenic is preferably 3000 ppm or less, more preferably 1500 ppm or less.

The composite oxide of S25 containing lithium, transition metals and oxygen preferably has a layered rocksalt crystal structure with few defects and strains. Therefore, it is preferable to use a composite oxide containing few impurities. If a composite oxide containing lithium, a transition metal, and oxygen contains many impurities, it is likely to have a crystal structure with many defects or strains.

<S31>
Next, the first mixture is mixed with a composite oxide containing lithium, transition metals and oxygen (S31). A composite oxide containing lithium, a transition metal and oxygen, and a first mixture M
The atomic ratio of ix1 to magnesium is complex oxide:Mg _Mix1 =1:y (0.
0005 ≤ y ≤ 0.03), complex oxide: Mg _Mix1 = 1: y (
0.001 ≤ y ≤ 0.01), and the composite oxide: Mg _Mix1 = 1
: about 0.005 is more preferable.

The mixing in S31 is preferably under milder conditions than the mixing in S12 so as not to destroy the particles of the composite oxide. Mixing can be dry or wet. For example, a ball mill, bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use, for example, zirconia balls as media.

<S32, S33>
The materials mixed above are recovered (S32) to obtain a second mixture (S33).

Note that although a method of adding a mixture of lithium fluoride and magnesium fluoride to a composite oxide is described in this embodiment, one embodiment of the present invention is not limited thereto. S33
Instead of the second mixture of (1), a mixture obtained by adding a magnesium source and a fluorine source to the starting material of the composite oxide and firing it may be used. In this case, the steps S11 to S14 and the steps S21 to S25 do not need to be separated, which is simple and highly productive.

Alternatively, lithium cobaltate to which magnesium and fluorine are added in advance may be used. If magnesium and fluorine-doped lithium cobaltate are used, S3
It is more convenient because the steps up to 2 can be omitted.

Furthermore, a magnesium source and a fluorine source may be further added to lithium cobaltate to which magnesium and fluorine have been added in advance.

<S34>
The second mixture is then heated. This step may be referred to as annealing or second heating to distinguish it from the previous heating step.

Annealing is preferably performed at an appropriate temperature and time. Appropriate temperature and time are
It varies depending on conditions such as the particle size and composition of the composite oxide containing S25 lithium, transition metal and oxygen. Lower temperatures or shorter times may be preferred for smaller particles than for larger particles.

It is preferable that the temperature drop time after annealing is, for example, 10 hours or more and 50 hours or less.

It is thought that when the second mixture is annealed, the material of the first mixture with a low melting point (for example, lithium fluoride, melting point 848° C.) is first melted and distributed on the surface layer of the composite oxide particles. It is then speculated that the presence of this molten material causes the melting point depression of the other material, causing the other material to melt. For example, magnesium fluoride (melting point 1263° C.) is thought to melt and distribute on the surface layer of the composite oxide particles.

It is believed that the elements contained in the first mixture distributed in the surface layer are dissolved in the composite oxide containing lithium, transition metals and oxygen.

The diffusion of the elements of this first mixture is faster on the surface and grain boundaries than inside the composite oxide particles. Therefore, magnesium and halogen are more concentrated at the surface and grain boundaries than inside. As will be described later, when the magnesium concentration on the surface and grain boundaries is high, the change in crystal structure can be more effectively suppressed.

<S35>
The material annealed as described above is recovered to obtain the positive electrode active material 100 which is one embodiment of the present invention.

The positive electrode active material 100 preferably contains nickel and manganese as transition metals. By using nickel and manganese as transition metals, for example, a secondary battery with high capacity and high safety can be realized. The positive electrode active material 100 preferably contains nickel and manganese, and the number of moles of manganese is 0.5 times or more the number of moles of nickel.
It is preferred to have a region that is less than or equal to 1.2 times, and more preferably to have a region that is greater than 1.2 times and less than 2 times. Further, the positive electrode active material 100 preferably contains nickel, manganese, and cobalt, the number of moles of manganese is 0.5 to 3 times the number of moles of nickel, and the number of moles of cobalt is 0. It is preferable to have a region that is 0.5 times or more and 2 times or less. Alternatively, positive electrode active material 100 preferably comprises nickel, manganese and cobalt, wherein the number of moles of manganese is greater than 1.2 times the number of moles of nickel.
It is preferable to have a region in which the number of moles of cobalt is less than two times and the number of moles of cobalt is 0.5 to 2 times the number of moles of nickel.

The atomic ratio of the transition metal included in the positive electrode active material 100 can be determined, for example, by inductively coupled plasma mass spectrometry (Inductively Coupled Plasma Mass Spectrometry).
metry: ICP-MS analysis method), energy dispersive X-ray spectroscopy (EDX: Ener
gy Dispersion X-ray Spectroscopy), Electron Energy-Loss Spectroscopy (EELS: Electron Energy-Loss Spectroscopy)
scopy), X-ray photoelectron spectroscopy (XPS: X-ray Photoelectron
Spectroscopy), etc. may be used for measurement.

[Structure of positive electrode active material]
FIG. 2 shows a crystal structure of a positive electrode active material of one embodiment of the present invention. Figure 2 shows the space group R-3
An example of the crystal structure of nickel-manganese-lithium cobaltate with m is shown.

≪Surface layer≫
It is preferable that magnesium is distributed throughout the particles of the positive electrode active material 100, and in addition, it is more preferable that the magnesium concentration in the surface layer of the particles is higher than the average of the entire particles. In other words, the particle surface is entirely covered with crystal defects, and moreover, lithium is released from the surface during charging. Therefore, it is a portion that tends to become unstable and easily start changing the crystal structure. If the magnesium concentration in the surface layer is high, the change in crystal structure can be suppressed more effectively. Further, when the magnesium concentration in the surface layer is high, it can be expected that the corrosion resistance to hydrofluoric acid generated by the decomposition of the electrolyte will be improved.

Also, it is preferable that the concentration of halogen such as fluorine in the surface layer portion of the positive electrode active material 100 is higher than the average of the entire particles. The presence of halogen in the surface layer, which is the area in contact with the electrolyte,
Corrosion resistance to hydrofluoric acid can be effectively improved.

Thus, it is preferable that the surface layer portion of the positive electrode active material 100 has a composition different from that of the inside, that is, the concentration of magnesium and fluorine is higher than that of the inside. Moreover, it is preferable that the composition has a stable crystal structure at room temperature. Therefore, the surface layer may have a crystal structure different from that of the inside. For example, at least part of the surface layer portion of the positive electrode active material 100 may have a rock salt crystal structure. When the surface layer and the interior have different crystal structures, it is preferable that the crystal orientations of the surface layer and the interior substantially match.

However, if the surface layer is only MgO or only a structure in which MgO and CoO (II) are dissolved,
As described above, the lithium intercalation and deintercalation paths are lost. Therefore, the surface layer must contain at least cobalt, lithium in the discharged state, and a path for intercalation and deintercalation of lithium. Also, the concentration of cobalt is preferably higher than that of magnesium.

≪Grain boundary≫
Furthermore, it is preferable that the concentration of magnesium in the grain boundaries of the positive electrode active material 100 and in the vicinity thereof is higher than in other regions inside. Moreover, it is preferable that the halogen concentration at the grain boundary and its vicinity is also high.

Similar to grain surfaces, grain boundaries are planar defects. Therefore, it tends to become unstable and the crystal structure tends to start changing. Therefore, if the magnesium concentration at and near the grain boundaries is high,
A change in crystal structure can be suppressed more effectively.

In addition, when the magnesium and halogen concentrations at and near the grain boundaries are high, even when cracks occur along the grain boundaries of the 100 particles of the positive electrode active material, the magnesium and halogen concentrations are high near the surfaces caused by the cracks. Become. Therefore, the corrosion resistance to hydrofluoric acid can be improved even in the positive electrode active material after cracks have occurred.

In this specification and the like, the vicinity of the grain boundary means a region from the grain boundary to about 10 nm.

It is preferable to measure the atomic number ratio of magnesium, fluorine, etc. using XPS, EDX, or the like. For example, when the positive electrode active material 100 is subjected to XPS analysis, the atomic ratio of magnesium contained in the positive electrode active material 100 is preferably 0.4 times or more and 1.5 times or less that of the transition metal, and 0.4
5 times or more and less than 1.00 times is more preferable. For example, when the positive electrode active material 100 has nickel, manganese, and cobalt as transition metals, the atomic ratio of magnesium is
It is preferably 0.4 times or more and 1.5 times or less, more preferably 0.45 times or more and less than 1.00 times the sum of the atomic ratios of manganese and cobalt. In addition, when EDX analysis was performed, the atomic ratio of magnesium included in the positive electrode active material 100 was 0.50 times or more than 0.020 times that of the transition metal.
It is preferably 0.025 times or more and 0.30 times or less, further preferably 0.030 times or more and 0.20 times or less. In addition, when XPS analysis is performed, the atomic ratio of fluorine included in the positive electrode active material 100 is preferably 0.05 to 1.5 times that of the transition metal, and more preferably 0.3 to 1.00 times. preferable.

≪Charging method≫
High voltage charging for making the above determination is, for example, a counter electrode lithium coin cell (CR2032
type, diameter 20 mm height 3.2 mm).

More specifically, the positive electrode can be obtained by coating a positive electrode current collector made of aluminum foil with a slurry obtained by mixing a positive electrode active material, a conductive aid, and a binder.

Lithium metal can be used as the counter electrode. When a material other than lithium metal is used for the counter electrode, the potential of the secondary battery and the potential of the positive electrode are different. Voltage and potential in this specification and the like are the potential of the positive electrode unless otherwise specified.

1 mol/L lithium hexafluorophosphate (LiPF ₆ ) is used as the electrolyte in the electrolytic solution, and the electrolytic solution contains ethylene carbonate (EC) and diethyl carbonate (DEC) in a ratio of EC:DEC=3:7 ( volume ratio) and 2 wt % vinylene carbonate (VC) can be used.

Polypropylene having a thickness of 25 μm can be used for the separator.

The cathode can and the anode can can be made of stainless steel (SUS).

The coin cell produced under the above conditions is charged at a constant current of 4.6V and 0.5C, and then charged at a constant voltage until the current reaches 0.01C. Note that 1C is 137 mA/g here. The temperature should be 25°C. After charging in this manner, the coin cell is dismantled in an argon atmosphere glove box and the positive electrode is taken out to obtain a positive electrode active material charged at a high voltage.
When performing various analyzes after this, it is preferable to handle in an argon atmosphere. For example, XRD can be performed in a sealed container with an argon atmosphere.

«XRD»
FIG. 3 is a diagram in which the (0 0 3) plane, (1 0 4) plane, and (1 0 1) plane are added to the crystal structure shown in FIG. Note that lithium atoms are not shown in FIG. 3 in order to make the drawing easier to see.

When the XRD pattern of the positive electrode active material of one embodiment of the present invention corresponds to the space group R-3m, 2θ
has one or more peaks in the vicinity of 18.5°, for example, a range of greater than 17.5° and less than 20°, and 2θ is in the vicinity of 37.0°, such as a range of greater than 36° and less than 38.5° and has one or more peaks in the vicinity of 45.0° 2θ, for example, in a range of greater than 43.5° and less than 46.5°.

When the XRD pattern of the positive electrode active material of one embodiment of the present invention corresponds to the space group R-3m, 18
. The peak near 5° corresponds to the (0 0 3) plane indicated by the solid line in FIG. 3, and the peak near 37.0° corresponds to the (1 0 1) plane indicated by the two-dot chain line in FIG. The peak near 45.0° corresponds to the (1 0 4) plane indicated by the dashed dotted line in FIG.

The lattice constant of the positive electrode active material changes due to desorption of lithium from the positive electrode active material during charging. At this time, the change in lattice constant in each direction of the a, b, and c axes is
It is preferable to change as evenly as possible. Here, evenly changing means that the anisotropy of crystal strain is smaller when the lattice constant changes in the process of charging and discharging. A small crystal strain anisotropy means, for example, a small change in the lattice constant ratio of each axis. For example, in the positive electrode active material of one embodiment of the present invention, it is preferable that the ratio between the lattice constants of the a-axis and the c-axis changes less during charging and discharging.

If the anisotropy of the crystal strain when changing from the charged state to the discharged state is large, the crystal structure tends to collapse, and the capacity may significantly decrease with repeated charge-discharge cycles. In the case where the anisotropy of strain is small, for example, strain may be small in the positive electrode using the positive electrode active material of one embodiment of the present invention.

Since the positive electrode active material of one embodiment of the present invention has low anisotropy of strain due to charging and discharging, it can maintain a favorable interface with the solid electrolyte even after the process of charging and discharging. Therefore, the positive electrode active material of one embodiment of the present invention is suitable for a secondary battery using a solid electrolyte.

As can be seen from the crystal structure shown in FIG. 2, lithium is distributed in a plane substantially perpendicular to the c-axis.
It is suggested that detachment of lithium tends to cause expansion and contraction in the c-axis direction of the crystal structure. In addition, if the expansion and contraction of the crystal structure in the c-axis direction can be suppressed, it may be possible to suppress the decrease in capacity due to charging and discharging, which is preferable.

From FIG. 3, the c-axis has a small angle with respect to the (1 0 1) plane. From this, it is considered that the expansion and contraction in the c-axis direction of the crystal contributes little to the change in the spacing of the (101) planes. on the other hand,(
The 0 0 3) plane is parallel to the c-axis and is considered to be significantly affected by the progress of the crystal along the c-axis. The (1 0 4) plane is also likely to be affected because of its large angle with the c-axis.

A lithium ion secondary battery in which the positive electrode active material of one embodiment of the present invention contains lithium, nickel, and manganese, the positive electrode active material is used for the positive electrode, and metallic lithium is used for the negative electrode, is heated at 25° C. for 4 hours. The value obtained by dividing the a-axis lattice constant by the c-axis lattice constant when constant current charging is performed until the current value reaches 0.01 C is defined as a_0/c_0,
Preferably, a_0/c_0 is greater than 0.198 and less than 0.202. Furthermore, the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis when constant current discharge is performed until the battery voltage reaches 2.5 V in an environment of 25 ° C. is defined as a_N/c_N, and a_0/c_0 is a_N/ c
It is preferably greater than 0.993 times and less than 1.02 times _N.

In addition, the positive electrode active material may have multiple phases. For example, the positive electrode active material of one embodiment of the present invention has a first phase and a second phase, and the phases may have different lattice constants. In each phase, the space group may be different, but more preferably the same.

When the positive electrode active material has a plurality of phases, the above-mentioned peak near 18.5°, 45.
When Rietveld analysis is performed on one or more of the peaks near 0° and the peaks near 37.0°, the peak has a half-value width of 0.5° or less or 0.3° or less. It may be separated into the above peaks.

When separated into two or more peaks, the positive electrode active material may have two or more phases in the Rietveld analysis.

The crystallite size obtained by analyzing the XRD pattern of the positive electrode active material of one embodiment of the present invention is, for example, greater than 10 nm and less than 500 nm, or greater than 30 nm and less than 300 nm.

This embodiment can be implemented in appropriate combination with other embodiments.

(Embodiment 2)
In this embodiment, examples of materials that can be used for a secondary battery including the positive electrode active material 100 described in the above embodiment will be described. In this embodiment, a secondary battery in which a positive electrode, a negative electrode, and an electrolytic solution are wrapped in an outer package will be described as an example.

[Positive electrode]
The positive electrode has a positive electrode active material layer and a positive electrode current collector.

<Positive electrode active material layer>
The positive electrode active material layer has at least a positive electrode active material. In addition to the positive electrode active material, the positive electrode active material layer may also contain other substances such as a film on the surface of the active material, a conductive aid, or a binder.

As the positive electrode active material, the positive electrode active material 100 described in the previous embodiment can be used. By using the positive electrode active material 100 described in the above embodiment, a secondary battery with high capacity and excellent cycle characteristics can be obtained.

A carbon material, a metal material, a conductive ceramic material, or the like can be used as the conductive aid. A fibrous material may also be used as the conductive aid. The content of the conductive aid with respect to the total amount of the active material layer is preferably 1 wt % or more and 10 wt % or less, more preferably 1 wt % or more and 5 wt % or less.

The conductive aid can form an electrically conductive network in the active material layer. The conductive aid can maintain the path of electrical conduction between the positive electrode active materials. By adding a conductive aid to the active material layer, an active material layer having high electrical conductivity can be realized.

Examples of conductive aids that can be used include natural graphite, artificial graphite such as mesocarbon microbeads, and carbon fiber. As carbon fibers, for example, carbon fibers such as mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers can be used. As carbon fiber,
Carbon nanofibers, carbon nanotubes, and the like can be used. Carbon nanotubes can be produced, for example, by vapor deposition. In addition, as a conductive aid,
For example, carbon materials such as carbon black (acetylene black (AB), etc.), graphite (graphite) particles, graphene, and fullerene can be used. Also, for example, copper,
Powders of metals such as nickel, aluminum, silver, and gold, metal fibers, conductive ceramic materials, and the like can be used.

Alternatively, a graphene compound may be used as the conductive aid.

Graphene compounds may have excellent electrical properties of having high electrical conductivity and excellent physical properties of having high flexibility and high mechanical strength. Also, the graphene compound has a planar shape. Graphene compounds enable surface contact with low contact resistance. Moreover, even if it is thin, it may have very high conductivity, and a small amount can efficiently form a conductive path in the active material layer. Therefore, it is preferable to use a graphene compound as a conductive aid because the contact area between the active material and the conductive aid can be increased. By using a spray drying apparatus, it is preferable to form a film of a graphene compound, which is a conductive additive, covering the entire surface of the active material. Moreover, it is preferable because the electrical resistance can be reduced in some cases. Here, it is particularly preferable to use, for example, graphene or multi-graphene or RGO as the graphene compound. Here, RGO refers to a compound obtained by reducing graphene oxide (GO), for example.

When using an active material with a small particle size, for example, an active material with a particle size of 1 μm or less, the specific surface area of the active material is large, and more conductive paths connecting the active materials are required. Therefore, the amount of conductive aid tends to increase, and the amount of supported active material tends to decrease relatively. When the supported amount of the active material is reduced, the capacity of the secondary battery is reduced. In such a case, it is particularly preferable to use a graphene compound as a conductive aid, since even a small amount of the graphene compound can efficiently form a conductive path, so that the supported amount of the active material does not decrease.

As an example, a cross-sectional configuration example in the case where a graphene compound is used as a conductive additive for the active material layer 200 will be described below.

FIG. 4A shows a vertical cross-sectional view of the active material layer 200. FIG. The active material layer 200 includes a granular positive electrode active material 100, a graphene compound 201 as a conductive aid, and a binder (not shown). Here, for example, graphene or multi-graphene may be used as the graphene compound 201 . Here, the graphene compound 201 preferably has a sheet-like shape. Further, the graphene compound 201 may have a sheet shape in which a plurality of multi-graphenes or (and) a plurality of graphenes are partially overlapped.

In the vertical cross section of the active material layer 200, the sheet-like graphene compounds 201 are dispersed substantially uniformly inside the active material layer 200, as shown in FIG. 4B. Although the graphene compound 201 is schematically represented by a thick line in FIG. 4B, it is actually a thin film having a thickness of a single layer or multiple layers of carbon molecules. Since the plurality of graphene compounds 201 are formed so as to partially cover the plurality of granular positive electrode active materials 100 or adhere to the surfaces of the plurality of granular positive electrode active materials 100, they are in surface contact with each other. .

Here, a mesh-like graphene compound sheet (hereinafter referred to as graphene compound net or graphene net) can be formed by bonding a plurality of graphene compounds. When the graphene net covers the active material, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of binder can be reduced or not used, and the ratio of the active material to the electrode volume and electrode weight can be improved. That is, the capacity of the secondary battery can be increased.

Here, it is preferable that graphene oxide be used as the graphene compound 201 and be mixed with an active material to form a layer to be the active material layer 200 and then be reduced. By using graphene oxide, which is highly dispersible in a polar solvent, to form the graphene compound 201 , the graphene compound 201 can be dispersed substantially uniformly inside the active material layer 200 . The graphene compound 201 remaining in the active material layer 200 partially overlaps with each other to reduce the graphene oxide by volatilizing and removing the solvent from the dispersion medium containing the uniformly dispersed graphene oxide.
A three-dimensional conductive path can be formed by dispersing to such an extent that they are in surface contact with each other. Note that graphene oxide may be reduced by heat treatment or by using a reducing agent, for example.

Therefore, unlike a granular conductive additive such as acetylene black that makes point contact with the active material, the graphene compound 201 enables surface contact with low contact resistance, so that a smaller amount of granular conductive additive is required than a normal conductive additive. Electrical conductivity between the positive electrode active material 100 and the graphene compound 201 can be improved. Therefore, the ratio of the positive electrode active material 100 in the active material layer 200 can be increased. Thereby, the discharge capacity of the secondary battery can be increased.

In addition, by using a spray drying apparatus in advance, the entire surface of the active material is covered with a graphene compound that is a conductive additive, and a conductive path can be formed with the graphene compound between the active materials. .

Examples of binders include styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-
It is preferred to use a rubber material such as a propylene-diene copolymer. Fluororubber can also be used as the binder.

Moreover, as a binder, it is preferable to use, for example, a water-soluble polymer. Polysaccharides, for example, can be used as the water-soluble polymer. As polysaccharides, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, and starch can be used. Further, it is more preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

Alternatively, binders include polystyrene, polymethyl acrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, and polytetrafluoro. Materials such as ethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, nitrocellulose, etc. are preferably used.

You may use a binder combining two or more among the above.

For example, a material having a particularly excellent viscosity adjusting effect may be used in combination with another material.
For example, although rubber materials and the like are excellent in adhesive strength and elasticity, it may be difficult to adjust the viscosity when they are mixed with a solvent. In such a case, for example, it is preferable to mix with a material having a particularly excellent viscosity-adjusting effect. For example, a water-soluble polymer may be used as a material having a particularly excellent viscosity-adjusting effect. Further, as the water-soluble polymer particularly excellent in the viscosity adjusting effect, the aforementioned polysaccharides such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose and diacetyl cellulose, cellulose derivatives such as regenerated cellulose, and starch are used. be able to.

The solubility of cellulose derivatives such as carboxymethyl cellulose can be increased by using a salt such as a sodium salt or an ammonium salt of carboxymethyl cellulose, and the effect as a viscosity modifier can be easily exhibited. When the solubility is increased, the dispersibility with the active material and other constituents can be enhanced when the electrode slurry is prepared. In this specification, the cellulose and cellulose derivatives used as binders for electrodes include:
The salts thereof shall also be included.

The water-soluble polymer stabilizes the viscosity by dissolving in water, and can stably disperse the active material and other materials combined as a binder, such as styrene-butadiene rubber, in the aqueous solution. In addition, since it has a functional group, it is expected to be stably adsorbed on the surface of the active material. In addition, many cellulose derivatives such as carboxymethyl cellulose are materials having functional groups such as hydroxyl groups and carboxyl groups, and due to the presence of functional groups, the macromolecules interact with each other, and the surface of the active material is widely covered. There is expected.

When the binder that covers or contacts the surface of the active material forms a film, it is expected to function as a passivation film to suppress the decomposition of the electrolytic solution. Here, the passive film is
It is a film that does not conduct electrons or has extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, decomposition of the electrolyte can be suppressed at the battery reaction potential. can. It is further desirable that the passivation film suppresses electrical conductivity and allows lithium ions to conduct.

<Positive collector>
As the positive electrode current collector, highly conductive materials such as metals such as stainless steel, gold, platinum, aluminum and titanium, and alloys thereof can be used. Moreover, it is preferable that the material used for the positive electrode current collector does not elute at the potential of the positive electrode. Alternatively, an aluminum alloy added with an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can be used. Alternatively, a metal element that forms silicide by reacting with silicon may be used. Metal elements that react with silicon to form silicide include zirconium,
Titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel and the like. The shape of the current collector may be foil, plate (sheet), mesh, punching metal, expanded metal, or the like. A current collector having a thickness of 5 μm or more and 30 μm or less is preferably used.

[Negative electrode]
The negative electrode has a negative electrode active material layer and a negative electrode current collector. Moreover, the negative electrode active material layer may have a conductive aid and a binder.

<Negative electrode active material>
As the negative electrode active material, for example, an alloy-based material, a carbon-based material, or the like can be used.

As the negative electrode active material, an element capable of performing charge-discharge reaction by alloying/dealloying reaction with lithium can be used. For example, silicon, tin, gallium, aluminum,
Materials containing at least one of germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such an element has a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh/g. Therefore, it is preferable to use silicon for the negative electrode active material. Compounds containing these elements may also be used.
For example, SiO, _Mg2Si , _Mg2Ge , SnO, _SnO2 , _Mg2Sn , _SnS2 ,
_{V2Sn3 , FeSn2} , _{CoSn2 , Ni3Sn2} , _{Cu6Sn5 , Ag3Sn} , Ag
_{3Sb , Ni2MnSb} , _CeSb3 , _LaSn3 , _La3Co2Sn7 , _{CoSb3 ,}
There are InSb, SbSn, and the like. Here, elements capable of undergoing charge-discharge reactions by alloying/dealloying reactions with lithium, compounds containing such elements, and the like are sometimes referred to as alloy-based materials.

In this specification and the like, SiO refers to silicon monoxide, for example. Alternatively, SiO is Si
It can also be expressed as _Ox . Here x preferably has a value close to one. For example, x is
0.2 or more and 1.5 or less are preferable, and 0.3 or more and 1.2 or less are more preferable.

As the carbon-based material, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotube, graphene, carbon black, or the like may be used.

Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Spherical graphite having a spherical shape can be used here as the artificial graphite. For example, MCMB may have a spherical shape and are preferred. MCMB is also relatively easy to reduce its surface area and may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

When lithium ions are inserted into graphite (at the time of formation of lithium-graphite intercalation compound)
shows a potential as low as lithium metal (0.05 V or more and 0.3 V or less vs. Li/
Li ⁺ ). This allows the lithium ion secondary battery to exhibit a high operating voltage. Furthermore, graphite is preferable because it has advantages such as relatively high capacity per unit volume, relatively small volume expansion, low cost, and high safety compared to lithium metal.

Further, titanium dioxide (TiO ₂ ), lithium titanium oxide (Li ₄
Ti ₅ O ₁₂ ), lithium-graphite intercalation compound (Li _x C ₆ ), niobium pentoxide (Nb ₂ O ₅
), tungsten oxide (WO ₂ ), and molybdenum oxide (MoO ₂ ).

Also, Li _3-x M _x N (M=Co, Ni, Cu) having a Li ₃ N-type structure, which is a composite nitride of lithium and a transition metal, can be used as the negative electrode active material. For example, Li2 _.
6Co0.4N3 exhibits a large charge/discharge capacity (900 mAh/g, 1890 mAh _/ ^cm3 ) _and is preferable.

When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, so that it can be combined with materials such as V ₂ O ₅ and Cr ₃ O ₈ that do not contain lithium ions as the positive electrode active material, which is preferable. . Note that even when a material containing lithium ions is used as the positive electrode active material, a composite nitride of lithium and a transition metal can be used as the negative electrode active material by preliminarily desorbing the lithium ions contained in the positive electrode active material.

A material that causes a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO) that do not form an alloy with lithium may be used as the negative electrode active material. Further, as materials in which a conversion reaction occurs, Fe ₂ O ₃ , CuO, Cu ₂ O, RuO ₂ , Cr ₂ O ₃
oxides such as CoS _0.89 , NiS, sulfides such as CuS, Zn ₃ N ₂ , Cu ₃ N, Ge
It also occurs in nitrides such as _3N4 , phosphides such _{as NiP2} , _FeP2 and _CoP3 , and fluorides such as _FeF3 and _BiF3 .

As the conductive aid and binder that the negative electrode active material layer can have, the same materials as the conductive aid and binder that the positive electrode active material layer can have can be used.

<Negative electrode current collector>
A material similar to that of the positive electrode current collector can be used for the negative electrode current collector. The negative electrode current collector is
It is preferable to use a material that does not alloy with carrier ions such as lithium.

[Electrolyte]
The electrolytic solution has a solvent and an electrolyte. As the solvent for the electrolytic solution, aprotic organic solvents are preferred, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, and dimethyl carbonate. (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate,
1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., or two of these The above can be used in any combination and ratio.

In addition, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, the internal temperature of the secondary battery rises due to internal short circuits, overcharging, etc. However, it is possible to prevent the secondary battery from exploding or catching fire. When a secondary battery is installed in a device such as a mobile terminal or a vehicle, the device may be used while the secondary battery is close to the user. If the secondary battery ruptures or catches fire, for example, the user, such as the human body, may be in danger. Since the solvent of the electrolytic solution contains the ionic liquid, the user can use the portable terminal, vehicle, etc., in which the secondary battery is mounted, in a safer state. Ionic liquids consist of cations and anions, including organic cations and anions. Organic cations used in the electrolytic solution include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Further, as an anion used in the electrolytic solution, 1
valent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkylphosphate anions. be done.

Further, examples of the electrolyte dissolved in the above solvent include LiPF ₆ , LiClO ₄ , L
_iAsF6 , _LiBF4 , _LiAlCl4 , LiSCN, LiBr, LiI, _{Li2SO
4 , Li2B10Cl10 , Li2B12Cl12 , LiCF3SO3 , LiC4F9S _ _
O3} , LiC _{( CF3SO2 ) 3} , LiC( _{C2F5SO2 ) 3} , LiN _{( CF3SO2}
) ₂ , LiN(C ₄ F ₉ SO ₂ )(CF ₃ SO ₂ ), LiN(C ₂ F ₅ SO ₂ ) ₂ or the like, or two or more thereof in any combination and ratio can be used in

A mixed solvent of an organic solvent and an ionic liquid may be used as a solvent for the electrolytic solution used in the secondary battery.

Electrolytes used in secondary batteries contain particulate matter and elements other than constituent elements of the electrolyte (hereinafter simply referred to as "
Also called "impurities". ), it is preferable to use a highly purified electrolytic solution having a low content of .
Specifically, the weight ratio of impurities to the electrolytic solution is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

Additives such as vinylene carbonate, propanesultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), LiBOB, and dinitrile compounds such as succinonitrile and adiponitrile may also be added to the electrolytic solution. good. The concentration of the material to be added may be, for example, 0.1 wt % or more and 5 wt % or less with respect to the entire solvent.

A polymer gel electrolyte obtained by swelling a polymer with an electrolytic solution may also be used.

By using the polymer gel electrolyte, the safety against leakage and the like is enhanced. Also, the thickness and weight of the secondary battery can be reduced.

As the polymer to be gelled, silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, fluorine polymer gel, and the like can be used.

As the polymer, for example, a polymer having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, etc., and a copolymer containing them can be used. For example PVDF and hexafluoropropylene (
HFP) copolymer PVDF-HFP can be used. The polymer formed may also have a porous geometry.

Further, instead of the electrolytic solution, a solid electrolyte having an inorganic material such as a sulfide system or an oxide system,
Solid electrolytes having polymeric materials such as PEO (polyethylene oxide) can be used. When a solid electrolyte is used, installation of separators and spacers becomes unnecessary. again,
Since the entire battery can be made solid, the risk of liquid leakage is eliminated, dramatically improving safety. By using the positive electrode of one embodiment of the present invention, for example, a favorable interface with a solid electrolyte can be maintained even after the process of charging and discharging a secondary battery.

[Separator]
Also, the secondary battery preferably has a separator. As a separator, for example,
Materials such as paper, non-woven fabric, glass fiber, ceramics, nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, and synthetic fibers using polyurethane can be used. It is preferable that the separator is processed into an envelope shape and arranged so as to enclose either the positive electrode or the negative electrode.

The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof. As the ceramic material, for example, aluminum oxide particles, silicon oxide particles, or the like can be used. As fluorine-based materials,
For example, PVDF, polytetrafluoroethylene, etc. can be used. Examples of polyamide materials that can be used include nylon and aramid (meta-aramid and para-aramid).

Coating with a ceramic-based material improves oxidation resistance, so deterioration of the separator during high-voltage charging and discharging can be suppressed, and the reliability of the secondary battery can be improved. In addition, when coated with a fluorine-based material, the separator and the electrode are more likely to adhere to each other, and the output characteristics can be improved. Coating with a polyamide-based material, particularly aramid, improves the heat resistance, so that the safety of the secondary battery can be improved.

For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid. Alternatively, a polypropylene film may be coated with a mixed material of aluminum oxide and aramid on the surface thereof in contact with the positive electrode, and coated with a fluorine-based material on the surface thereof in contact with the negative electrode.

When a separator having a multilayer structure is used, the safety of the secondary battery can be maintained even if the thickness of the entire separator is thin, so that the capacity per unit volume of the secondary battery can be increased.

[Exterior body]
For example, a metal material such as aluminum or a resin material can be used as an exterior body of the secondary battery. Moreover, a film-like exterior body can also be used. As a film, for example, a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc. is provided with a highly flexible metal thin film such as aluminum, stainless steel, copper, nickel, etc., and an exterior is provided on the metal thin film. A film having a three-layer structure provided with an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin can be used as the outer surface of the body.

[Charging and discharging method]
Charging and discharging of the secondary battery can be performed, for example, as follows.

≪CC charging≫
First, CC charging will be described as one of charging methods. CC charging is a charging method in which a constant current is passed through the secondary battery throughout the charging period and charging is stopped when a predetermined voltage is reached. A secondary battery is assumed to be an equivalent circuit of internal resistance R and secondary battery capacity C as shown in FIG. 5(A). In this case, the secondary battery voltage _VB is the voltage V _R applied to the internal resistance R and the secondary battery capacity C
is the sum of the voltages _VC across

During CC charging, as shown in FIG. 5A, the switch is turned on and a constant current I flows through the secondary battery. Since the current I is constant during this period, the voltage V _R applied to the internal resistance R is also constant according to Ohm's law of V _R =R×I. On the other hand, the voltage V _C applied to the secondary battery capacity C rises with time. Therefore, the secondary battery voltage _VB increases over time.

Then, when the secondary battery voltage _VB reaches a predetermined voltage, for example 4.3V, charging is stopped. When CC charging is stopped, the switch is turned off and the current I=
becomes 0. Therefore, the voltage VR applied to the internal resistance _R becomes 0V. Therefore, the internal resistance R
The secondary battery voltage _VB drops by an amount corresponding to the voltage drop at .

FIG. 5C shows an example of the secondary battery voltage _VB and charging current during CC charging and after CC charging is stopped. The secondary battery voltage _VB , which had increased during CC charging,
It shows a slight decrease after CC charging is stopped.

≪CCCV charging≫
Next, CCCV charging, which is a different charging method from the above, will be described. CCCV charging is
In this charging method, the battery is first charged to a predetermined voltage by CC charging, and then charged by CV (constant voltage) charging until the flowing current decreases, specifically, until the terminal current value is reached.

During CC charging, as shown in FIG.
The switch of the constant voltage power supply is turned off, and a constant current I flows through the secondary battery. During this time, the current I
is constant, the voltage V _R across the internal resistance R is also constant according to Ohm's law of V _R =R×I. On the other hand, the voltage V _C applied to the secondary battery capacity C rises with time.
Therefore, the secondary battery voltage _VB increases over time.

Then, when the secondary battery voltage _VB reaches a predetermined voltage, for example, 4.3 V, the CC charging is switched to the CV charging. During CV charging, as shown in FIG. 6B, the switch of the constant-voltage power supply is turned on, the switch of the constant-current power supply is turned off, and the secondary battery voltage _VB becomes constant. On the other hand, the voltage V _C applied to the secondary battery capacity C rises with time. V _B =V
Since _{R 1} +V _C , the voltage V _R across the internal resistance R decreases over time.
As the voltage V _R applied to the internal resistance R becomes smaller, according to Ohm's law of V _R =R×I,
The current I flowing through the secondary battery also decreases.

Then, when the current I flowing through the secondary battery reaches a predetermined current, for example, a current corresponding to 0.01C, charging is stopped. When CCCV charging is stopped, all switches are turned off and current I=0, as shown in FIG. 6(C). Therefore, the voltage VR applied to the internal resistance _R becomes 0V. However, since the voltage _VR applied to the internal resistance R is sufficiently reduced by CV charging, the secondary battery voltage _VB hardly drops even if the voltage drop across the internal resistance R disappears.

FIG. 6D shows an example of the secondary battery voltage _VB and charging current during CCCV charging and after CCCV charging is stopped. It shows that the secondary battery voltage _VB hardly drops even if the CCCV charging is stopped.

≪CC Discharge≫
Next, CC discharge, which is one of the discharge methods, will be described. CC discharge is a discharge method in which a constant current is supplied from the secondary battery throughout the discharge period, and discharge is stopped when the secondary battery voltage _VB reaches a predetermined voltage, for example, 2.5V.

FIG. 7 shows an example of the secondary battery voltage _VB and the discharge current during CC discharge. It shows how the secondary battery voltage _VB drops as the discharge progresses.

Next, the discharge rate and charge rate will be explained. Discharge rate is the relative ratio of current during discharge to battery capacity and is expressed in units of C. In a battery with a rated capacity of X (Ah), the current corresponding to 1C is X (A). When discharged at a current of 2X (A), 2
When discharging at a current of X/5 (A), it is said to discharge at 0.2C. In addition, the charging rate is the same. When charging at a current of 2X (A), it is said to charge at 2C, and when charging at a current of X/5 (A), it is said to charge at 0.2C. It is said that

This embodiment can be implemented in appropriate combination with other embodiments.

(Embodiment 3)
In this embodiment, an ionic liquid that can be used as an electrolyte in a secondary battery of one embodiment of the present invention will be described. As a solvent for the electrolytic solution, a plurality of ionic liquids described below may be mixed and used.

One or more types of ionic liquids may be used in combination. The ionic liquid consists of cations and anions, and includes organic cations and anions.

As the organic cation, it is preferable to use, for example, an aromatic cation, an aliphatic onium cation such as a quaternary ammonium cation, a tertiary sulfonium cation, and a quaternary phosphonium cation.

The aromatic cation is preferably, for example, a cation containing a five-membered heteroaromatic ring. The cation containing a 5-membered heteroaromatic ring is a benzimidazolium cation,
There are benzoxazolium cations, benzothiazolium cations, and the like. Examples of cations containing a five-membered heteroaromatic ring, which are monocyclic compounds, include oxazolium cations, thiazolium cations, isoxazolium cations, isothiazolium cations, imidazolium cations, pyrazolium cations, and the like. . compound stability, viscosity and ionic conductivity,
In addition, from the viewpoint of ease of synthesis, a cation containing a five-membered heteroaromatic ring, which is a monocyclic compound, is preferred, and imidazolium cations are more preferred because they are expected to reduce the viscosity.

Examples of anions in the ionic liquid include monovalent amide anion, monovalent methide anion, fluorosulfonate anion (SO ₃ F ⁻ ), fluoroalkylsulfonate anion, tetrafluoroborate (BF ₄ ⁻ ), fluoroalkyl borate, hexafluorophosphate (PF ₆ ⁻ ), fluoroalkyl phosphate, and the like. As the monovalent amide anion, (C _n F _2n+1 SO ₂ ) ₂ N ⁻ (n=
0 or more and 3 or less), and monovalent cyclic amide anions include (CF ₂ SO ₂ ) ₂ N ^— and the like. As the monovalent methide anion, (C _n F _2n+1 SO ₂ ) ₃ C ⁻ (n=0 or more 3
below), and the monovalent cyclic methide anion is (CF ₂ SO ₂ ) ₂ C ⁻ (CF ₃ SO ₂
)and so on. As the fluoroalkylsulfonate anion, (C _m F _2m+1 SO ₃
) ^- (m = 0 or more and 4 or less). As the fluoroalkyl borate, {BF _n (
C _m H _k F _2m+1−k ) _4−n } ⁻ (n=0 to 3, m=1 to 4, k=0 to 2m). As fluoroalkyl phosphates, {PF _n (C _m H _k
F _2m+1−k ) _6−n } ⁻ (n=0 to 5, m=1 to 4, k=0 to 2m). In addition, the said anion is not restricted to these.

As the ionic liquid having a cation containing a five-membered heteroaromatic ring, for example, the general formula (G
1).

In general formula (G1), R ¹ represents an alkyl group having 1 to 4 carbon atoms, and R ²
to R ⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ⁵ is two or more selected from atoms of C, O, Si, N, S, and P; Represents the main chain composed, A ^- is a monovalent imide anion, a sulfonylimide (also called sulfonylamide according to IUPAC nomenclature) anion, a monovalent amide anion, a monovalent methide anion,
It represents any one of a fluorosulfonate anion, a fluoroalkylsulfonate anion, a tetrafluoroborate anion, a fluoroalkylborate anion, a hexafluorophosphate anion, or a fluoroalkylphosphate anion.

Also, a substituent may be introduced into the main chain of ^R5 . Examples of substituents to be introduced include alkyl groups and alkoxy groups.

Note that the alkyl group in the ionic liquid represented by General Formula (G1) may be linear or branched. For example, ethyl group, tert-butyl group. Further, in the ionic liquid represented by general formula (G1), R ⁵ preferably does not have an oxygen-oxygen bond (peroxide). Oxygen-oxygen single bonds are very fragile and can be explosive due to their high reactivity. Therefore, it is not suitable for power storage devices.

The ionic liquid may also contain a 6-membered heteroaromatic ring. For example, the following general formula (G
The ionic liquid represented by 2) can be used.

In general formula (G2), R ⁶ represents a main chain composed of two or more atoms selected from C, O, Si, N, S, and P, and R ⁷ to R ¹¹ each independently ^represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; represents any one of monovalent methide anion, fluorosulfonate anion, fluoroalkylsulfonate anion, tetrafluoroborate anion, fluoroalkylborate anion, hexafluorophosphate anion, or fluoroalkylphosphate anion.

Also, a substituent may be introduced into the main chain of ^R6 . Examples of substituents to be introduced include alkyl groups and alkoxy groups.

Further, as an ionic liquid having a quaternary ammonium cation, for example, the following general formula (G
An ionic liquid represented by 3) can be used.

In general formula (G3), R ¹² to R ¹⁷ each independently represent an alkyl group having 1 to 20 carbon atoms, a methoxy group, a methoxymethyl group, a methoxyethyl group, or a hydrogen atom.

As the ionic liquid, for example, an ionic liquid composed of a quaternary ammonium cation and a monovalent anion and represented by the following general formula (G4) can be used.

In general formula (G4), R ¹⁸ to R ²⁴ each independently represent an alkyl group having 1 to 20 carbon atoms, a methoxy group, a methoxymethyl group, a methoxyethyl group, or a hydrogen atom.

As the ionic liquid, for example, an ionic liquid composed of a quaternary ammonium cation and a monovalent anion and represented by the following general formula (G5) can be used.

In general formula (G5), n and m are 1 or more and 3 or less. α is 0 or more and 6 or less, when n is 1, α is 0 or more and 4 or less, when n is 2, α is 0 or more and 5 or less, and when n is 3, α is 0 or more and 6 or less. β is 0 or more and 6 or less, and when m is 1, β is 0 or more and 4 or less, and m
is 2, β is 0 or more and 5 or less, and when m is 3, β is 0 or more and 6 or less. Note that α or β being 0 means unsubstituted. Also, the case where both α and β are 0 shall be excluded. X or Y is, as a substituent, a linear or side-chain alkyl group having 1 to 4 carbon atoms, a linear or side-chain alkoxy group having 1 to 4 carbon atoms, or a carbon number 1 or more and 4 or less linear or side chain alkoxyalkyl groups are represented. A 1 ⁻ represents any one of a monovalent amide anion, a monovalent methide anion, a perfluoroalkylsulfonate anion, a tetrafluoroborate anion, a perfluoroalkylborate anion, a hexafluorophosphate anion and a perfluoroalkylphosphate anion.

In the quaternary spiro ammonium cation, the two aliphatic rings forming the spiro ring are either 5-, 6-, or 7-membered rings.

Specific examples of the cation of general formula (G1) include structural formulas (111) to (
174).

This embodiment can be implemented in appropriate combination with other embodiments.

(Embodiment 4)
In this embodiment, an example of the shape of a secondary battery including the positive electrode active material 100 described in the above embodiment will be described. The description of the above embodiment can be referred to for materials used for the secondary battery described in this embodiment.

[Coin-type secondary battery]
First, an example of a coin-type secondary battery will be described. FIG. 8A is an external view of a coin-type (single-layer flat type) secondary battery, and FIG. 8B is a cross-sectional view thereof.

In a coin-type secondary battery 300, a positive electrode can 301, which also functions as a positive electrode terminal, and a negative electrode can 302, which also functions as a negative electrode terminal, are insulated and sealed with a gasket 303 made of polypropylene or the like. The positive electrode 304 includes a positive electrode current collector 305 and a positive electrode active material layer 30 provided in contact therewith.
6. Further, the negative electrode 307 is formed of a negative electrode current collector 308 and a negative electrode active material layer 309 provided so as to be in contact therewith.

Note that the active material layers of the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 may be formed only on one side.

For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, and titanium that are corrosion resistant to the electrolyte, alloys thereof, and alloys of these and other metals (for example, stainless steel) can be used. can. Also, in order to prevent corrosion due to the electrolyte, it is preferable to coat with nickel, aluminum, or the like. The positive electrode can 301 is the positive electrode 304, and the negative electrode can 302 is the negative electrode 3.
07 are electrically connected.

These negative electrode 307, positive electrode 304 and separator 310 are impregnated with an electrolyte, and
), with the positive electrode can 301 facing downward, the positive electrode 304, the separator 310, the negative electrode 307,
The negative electrode cans 302 are stacked in this order, and the positive electrode can 301 and the negative electrode can 302 are pressure-bonded via a gasket 303 to manufacture the coin-shaped secondary battery 300 .

By using the positive electrode active material described in the above embodiment for the positive electrode 304, the coin-shaped secondary battery 300 with high capacity and excellent cycle characteristics can be obtained.

Here, the current flow during charging of the secondary battery will be described with reference to FIG. When a secondary battery using lithium is regarded as one closed circuit, the movement of lithium ions and the flow of current are in the same direction. In secondary batteries using lithium, the anode (anode) and the cathode (cathode) are switched between charging and discharging, and the oxidation reaction and the reduction reaction are switched, so the electrode with a high reaction potential is called a positive electrode. An electrode with a low reaction potential is called a negative electrode. Therefore, in this specification, the positive electrode is the “positive electrode” or “positive electrode” or “positive electrode” during charging, discharging, reverse pulse current, or charging current. A negative electrode is called a “negative electrode” or a “negative electrode”. The use of the terms anode and cathode in relation to oxidation and reduction reactions can be confusing as they are reversed during charging and discharging. Accordingly, the terms anode and cathode are not used herein. If the terms anode or cathode are used, specify whether it is charging or discharging, and refer to the positive electrode (
The positive electrode) and the negative electrode (negative electrode) are also indicated.

A charger is connected to two terminals shown in FIG. 8C to charge the secondary battery 300 . As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[Cylindrical secondary battery]
Next, an example of a cylindrical secondary battery will be described with reference to FIG. Cylindrical secondary battery 600
has a positive electrode cap (battery cover) 601 on its top surface and battery cans (armor cans) 602 on its side and bottom surfaces, as shown in FIG. 9A. These positive electrode caps and battery cans (outer cans) 6
02 is insulated by a gasket (insulating packing) 610 .

FIG. 9B is a diagram schematically showing a cross section of a cylindrical secondary battery. A battery element in which a strip-shaped positive electrode 604 and a strip-shaped negative electrode 606 are wound with a separator 605 interposed therebetween is provided inside a hollow columnar battery can 602 . Although not shown, the battery element is wound around a center pin. Battery can 602 is closed at one end and open at the other end. The battery can 602 can be made of a metal such as nickel, aluminum, or titanium that is resistant to corrosion by the electrolyte, an alloy thereof, or an alloy of these metals with another metal (for example, stainless steel). . Also, in order to prevent corrosion due to the electrolyte, it is preferable to coat with nickel, aluminum, or the like. Inside the battery can 602 , the battery element in which the positive electrode, the negative electrode and the separator are wound is sandwiched between a pair of insulating plates 608 and 609 facing each other. A non-aqueous electrolyte (not shown) is filled inside the battery can 602 in which the battery element is provided. The non-aqueous electrolyte is
A battery similar to a coin-type secondary battery can be used.

Since the positive electrode and the negative electrode used in a cylindrical storage battery are wound, it is preferable to form the active material on both sides of the current collector. A positive electrode terminal (positive collector lead) 603 is connected to the positive electrode 604 , and a negative electrode terminal (negative collector lead) 607 is connected to the negative electrode 606 . A metal material such as aluminum can be used for both the positive terminal 603 and the negative terminal 607 . positive terminal 6
03 is resistance welded to the safety valve mechanism 612, and the negative electrode terminal 607 is resistance welded to the bottom of the battery can 602, respectively. The safety valve mechanism 612 is a PTC element (Positive Temperature C
effective) 611 to the positive electrode cap 601 .
The safety valve mechanism 612 closes the positive electrode cap 601 when the increase in internal pressure of the battery exceeds a predetermined threshold.
and the positive electrode 604 are disconnected. The PTC element 611 is a thermal resistance element whose resistance increases when the temperature rises, and the increase in resistance limits the amount of current to prevent abnormal heat generation. Barium titanate (BaTiO ₃ ) semiconductor ceramics or the like can be used for the PTC element.

Moreover, as shown in FIG.
The module 615 may be constructed by being sandwiched between. The plurality of secondary batteries 600 may be connected in parallel, may be connected in series, or may be connected in series after being connected in parallel. By configuring a module 615 having a plurality of secondary batteries 600,
A large amount of power can be extracted.

FIG. 9D is a top view of the module 615. FIG. The conductive plate 613 is shown in dashed lines for clarity of illustration. As shown in FIG. 9D, the module 615 may have conductors 616 that electrically connect the plurality of secondary batteries 600 . A conductive plate may be provided overlying the conductor 616 . Also, a temperature control device 617 may be provided between the plurality of secondary batteries 600 . When the secondary battery 600 is overheated, it is cooled by the temperature control device 617 and the secondary battery 60
If the 0 is too cold, it can be heated by the temperature controller 617 . Therefore, the performance of the module 615 is less affected by the outside air temperature. It is preferable that the heat medium included in the temperature control device 617 has insulation and nonflammability.

Since the module 615 has the temperature control device 617, the temperature of the secondary battery 600 can be changed according to the desired performance. For example, heating the secondary battery 600 enables charging and discharging at a higher current density. For example, charging time can be shortened. Moreover, when the secondary battery 600 is heated, the solvent of the electrolyte solution of the secondary battery 600 preferably contains an ionic liquid. Since the ionic liquid can suppress an increase in vapor pressure during heating as compared with an organic solvent, swelling of the secondary battery 600 can be suppressed even when heating is performed. That is, performance can be improved by heating while ensuring safety.

Module 615 may have, for example, other storage batteries in addition to secondary battery 600 . For example, module 615 may include storage batteries such as lead-acid batteries, electric double layer capacitors, lithium-ion capacitors, and the like. These storage batteries may be used to activate and operate the temperature control device 617 .

By using the positive electrode active material described in the above embodiment for the positive electrode 604, the cylindrical secondary battery 600 with high capacity and excellent cycle characteristics can be obtained.

[Structural example of secondary battery]
Another structural example of the secondary battery is described with reference to FIGS.

10A and 10B are external views of secondary batteries. The secondary battery has a circuit board 900 and a secondary battery 913 . A label 910 is attached to the secondary battery 913 . Further, as shown in FIG. 10B, the secondary battery has terminals 951 and 95
2, an antenna 914, and an antenna 915.

The circuit board 900 has terminals 911 and a circuit 912 . Terminal 911 is connected to terminal 95
1, terminal 952, antenna 914, antenna 915, and circuit 912; Note that a plurality of terminals 911 may be provided and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, or the like.

The circuit 912 may be provided on the back surface of the circuit board 900 . Note that the antenna 914
And the antenna 915 is not limited to a coil shape, and may have a linear shape or a plate shape, for example. Further, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas may be used. Or antenna 914 or antenna 915
may be a flat conductor. This flat conductor can function as one of conductors for electric field coupling. That is, the antenna 914 or 915 may function as one of the two conductors of the capacitor. As a result, electric power can be exchanged not only by electromagnetic fields and magnetic fields, but also by electric fields.

The line width of antenna 914 is preferably greater than the line width of antenna 915 . Accordingly, the amount of power received by the antenna 914 can be increased.

The secondary battery has a layer 916 between the antennas 914 and 915 and the secondary battery 913 .
have The layer 916 has a function of shielding an electromagnetic field generated by the secondary battery 913, for example. A magnetic material, for example, can be used as the layer 916 .

Note that the structure of the secondary battery is not limited to that shown in FIG.

For example, as shown in FIGS. 11(A-1) and 11(A-2), FIGS.
An antenna may be provided on each of a pair of opposing surfaces of the secondary battery 913 illustrated in 0B. FIG. 11(A-1) is an external view of the pair of surfaces viewed from one side.
(A-2) is an external view seen from the other side of the pair of surfaces. Note that the description of the secondary battery illustrated in FIGS. 10A and 10B can be used as appropriate for the same portions as those of the secondary battery illustrated in FIGS. 10A and 10B.

As shown in FIG. 11A-1, an antenna 914 is provided on one of a pair of surfaces of a secondary battery 913 with a layer 916 interposed therebetween, and as shown in FIG. An antenna 915 is provided with a layer 917 interposed on the other of the pair of surfaces. Layer 917 is, for example, secondary battery 9
It has the function of shielding the electromagnetic field caused by 13. A magnetic material, for example, can be used as the layer 917 .

With the above structure, the size of both antenna 914 and antenna 918 can be increased. The antenna 918 has a function of performing data communication with an external device, for example. An antenna having a shape applicable to the antenna 914 can be applied to the antenna 918, for example. As a communication method between the secondary battery and the other device via the antenna 918, a response method such as NFC that can be used between the secondary battery and the other device can be applied.

Alternatively, as shown in FIG. 11B-1, a display device 920 may be provided in the secondary battery 913 shown in FIGS. 10A and 10B. The display device 920 is electrically connected to the terminals 911 . Note that the label 910 may not be provided in the portion where the display device 920 is provided. Note that the same parts as those of the secondary battery shown in FIGS. 10A and 10B are shown in FIG.
and the description of the secondary battery illustrated in FIG. 10B can be used as appropriate.

The display device 920 may display, for example, an image indicating whether or not the battery is being charged, an image indicating the amount of stored electricity, and the like. As the display device 920, electronic paper, a liquid crystal display device, an electroluminescence (also referred to as EL) display device, or the like can be used, for example. For example, by using electronic paper, power consumption of the display device 920 can be reduced.

Alternatively, as shown in FIG. 11B-2, a sensor 921 may be provided in the secondary battery 913 shown in FIGS. 10A and 10B. Sensor 921 is connected to terminal 911 via terminal 922 .
is electrically connected to Note that the description of the secondary battery illustrated in FIGS. 10A and 10B can be used as appropriate for the same portions as those of the secondary battery illustrated in FIGS. 10A and 10B.

As the sensor 921, for example, displacement, position, speed, acceleration, angular velocity, number of revolutions, distance,
light, fluid, magnetism, temperature, chemicals, sound, time, hardness, electric field, current, voltage, power, radiation,
It is sufficient to have a function capable of measuring flow rate, humidity, gradient, vibration, smell, or infrared rays. By providing the sensor 921 , for example, data (such as temperature) indicating the environment in which the secondary battery is placed can be detected and stored in the memory in the circuit 912 .

Further, structural examples of the secondary battery 913 are described with reference to FIGS.

A secondary battery 913 illustrated in FIG. 12A includes a wound body 950 provided with a terminal 951 and a terminal 952 inside a housing 930 . The wound body 950 is impregnated with the electrolytic solution inside the housing 930 . The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In addition, in FIG. 12A, the housing 930 is shown separately for the sake of convenience.
52 extends out of housing 930 . As the housing 930, a metal material (such as aluminum) or a resin material can be used.

Note that as shown in FIG. 12B, the housing 930 shown in FIG. 12A may be formed using a plurality of materials. For example, in a secondary battery 913 illustrated in FIG. 12B, a housing 930a and a housing 930b are attached to each other, and a wound body 950 is provided in a region surrounded by the housings 930a and 930b. .

An insulating material such as an organic resin can be used for the housing 930a. In particular, by using a material such as an organic resin for the surface on which the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by the housing 930a is small, the housing 930a
An antenna such as the antenna 914 or the antenna 915 may be provided inside. Housing 930b
For example, a metal material can be used as the material.

Furthermore, the structure of the wound body 950 is shown in FIG. The wound body 950 includes a negative electrode 931,
It has a positive electrode 932 and a separator 933 . The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are laminated with the separator 933 interposed therebetween, and the laminated sheet is wound. Note that the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked more than once.

The negative electrode 931 is connected to the terminal 911 shown in FIG. 10 through one of the terminals 951 and 952 . The positive electrode 932 is connected to the terminal 9 shown in FIG. 10 through the other of the terminals 951 and 952.
11.

By using the positive electrode active material described in the above embodiment for the positive electrode 932, the secondary battery 913 can have high capacity and excellent cycle characteristics.

[Laminate type secondary battery]
Next, examples of laminated secondary batteries are described with reference to FIGS.
If the laminate-type secondary battery has a flexible structure and is mounted in an electronic device having at least a part of the flexible portion, the secondary battery can be bent according to the deformation of the electronic device. can.

A laminated secondary battery 980 will be described with reference to FIG. A laminated secondary battery 980 includes a wound body 993 illustrated in FIG. The wound body 993 is the negative electrode 99
4, a positive electrode 995, and a separator 996. A wound body 993 is obtained by laminating a negative electrode 994 and a positive electrode 995 with a separator 996 interposed therebetween, and winding the laminated sheet, similarly to the wound body 950 described in FIG.

Note that the number of laminated layers composed of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed according to the required capacity and device volume. The negative electrode 994 is connected to a negative current collector (not shown) through one of the lead electrodes 997 and 998, and the positive electrode 995 is connected to a positive current collector (not shown) through the other of the lead electrodes 997 and 998. connected).

As shown in FIG. 14(B), a film 981 serving as an exterior body and a film 9 having a concave portion
A secondary battery 980 can be manufactured as shown in FIG. winding body 9
93 has a lead electrode 997 and a lead electrode 998, and is impregnated with an electrolytic solution inside film 981 and film 982 having recesses.

For the film 981 and the film 982 having recesses, for example, a metal material such as aluminum or a resin material can be used. Film 981 and film 982 with recesses
If a resin material is used as the material of , the film 981 and the film 982 having the concave portion can be deformed when force is applied from the outside, and a flexible storage battery can be manufactured.

14(B) and 14(C) show an example using two films, one film is folded to form a space, and the wound body 9 described above is formed in the space.
93 may be stored.

By using the positive electrode active material described in the above embodiment for the positive electrode 995, the secondary battery 980 can have high capacity and excellent cycle characteristics.

14, an example of the secondary battery 980 having the wound body in the space formed by the film serving as the exterior body is described. For example, as shown in FIG. A secondary battery having a plurality of strip-shaped positive electrodes, separators, and negative electrodes may be used.

A laminated secondary battery 500 illustrated in FIG. 15A includes a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, It has a separator 507 , an electrolytic solution 508 , and an exterior body 509 . A separator 507 is provided between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509 . Further, the inside of the exterior body 509 is filled with an electrolytic solution 508 . The electrolytic solution 508 includes
The electrolyte solution described in Embodiment Mode 2 can be used.

In the laminated secondary battery 500 illustrated in FIG. 15A, the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for electrical contact with the outside. Therefore, part of the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged so as to be exposed to the outside from the exterior body 509 . In addition, the positive electrode current collector 501 and the negative electrode current collector 504 are not exposed to the outside from the outer package 509, and the lead electrode and the positive electrode current collector 501 or the negative electrode current collector 504 are ultrasonically bonded using a lead electrode. The lead electrodes may be exposed to the outside.

In the laminate-type secondary battery 500, the exterior body 509 includes a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, and the like.
A three-layer structure in which a highly flexible metal thin film made of aluminum, stainless steel, copper, nickel, etc. is provided, and an insulating synthetic resin film such as polyamide resin, polyester resin, etc. is provided on the metal thin film as the outer surface of the exterior body. A structured laminate film can be used.

An example of a cross-sectional structure of a laminated secondary battery 500 is shown in FIG. Figure 15
In (A), for the sake of simplification, an example in which two current collectors are used is shown, but in reality, it is composed of a plurality of electrode layers.

In FIG. 16B, the number of electrode layers is 16 as an example. Note that the secondary battery 500 has flexibility even with 16 electrode layers. FIG. 15B shows a structure with eight negative electrode current collectors 504 and eight positive electrode current collectors 501, for a total of 16 layers. Note that FIG. 15B shows a cross section of a negative electrode lead-out portion, in which eight layers of negative electrode current collectors 504 are ultrasonically bonded. Of course, the number of electrode layers is not limited to 16, and may be more or less. When the number of electrode layers is large, the secondary battery can have a larger capacity. In addition, when the number of electrode layers is small, the thickness of the secondary battery can be reduced and the secondary battery can be excellent in flexibility.

16 and 17 show an example of an external view of a laminated secondary battery 500. FIG. 16 and 17 have a positive electrode 503, a negative electrode 506, a separator 507, an outer package 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511. FIG.

FIG. 18A shows an external view of the positive electrode 503 and the negative electrode 506. FIG. The positive electrode 503 is the positive electrode current collector 5
01 , and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501 . In addition, the positive electrode 503 has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504 , and the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504 . Further, the negative electrode 506 has a region where the negative electrode current collector 504 is partially exposed, that is, a tab region. The area and shape of the tab regions of the positive and negative electrodes are not limited to the example shown in FIG.

[Method for producing laminated secondary battery]
Here, an example of a method for manufacturing a laminated secondary battery whose appearance is shown in FIG.
8(B) and (C).

First, the negative electrode 506, the separator 507, and the positive electrode 503 are laminated. FIG. 18B shows the negative electrode 506, the separator 507, and the positive electrode 503 which are stacked. Here, an example is shown in which five sets of negative electrodes and four sets of positive electrodes are used. Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For joining, for example, ultrasonic welding or the like may be used. Similarly, bonding between the tab regions of the negative electrode 506 and bonding of the negative electrode lead electrode 511 to the tab region of the outermost negative electrode are performed.

Next, the negative electrode 506 , the separator 507 , and the positive electrode 503 are arranged over the exterior body 509 .

Next, as shown in FIG. 18C, the exterior body 509 is bent at the portion indicated by the broken line. After that, the outer peripheral portion of the exterior body 509 is joined. For example, thermocompression bonding or the like may be used for joining. At this time, a portion (or one side) of the exterior body 509 is
A region (hereinafter referred to as an introduction port) that is not joined to the

Next, the electrolytic solution 508 is introduced into the exterior body 509 through an inlet provided in the exterior body 509 . It is preferable to introduce the electrolytic solution 508 under a reduced pressure atmosphere or an inert atmosphere. And finally, the inlet is joined. In this manner, the secondary battery 500, which is a laminated secondary battery, can be manufactured.

By using the positive electrode active material described in the above embodiment for the positive electrode 503, the secondary battery 500 can have high capacity and excellent cycle characteristics.

[Bendable secondary battery]
Next, an example of a bendable secondary battery will be described with reference to FIGS. 19 and 20. FIG.

FIG. 19A shows a schematic top view of a bendable secondary battery 500 . Figure 19 (B
1), (B2), and (C) are the cutting lines C1-C2 and C3 in FIG. 19A, respectively.
-C4, a schematic cross-sectional view at section line A1-A2. The battery 50 has an exterior body 51 , and a positive electrode 11 a and a negative electrode 11 b housed inside the exterior body 51 . A lead 12 a electrically connected to the positive electrode 11 a and a lead 12 b electrically connected to the negative electrode 11 b extend outside the exterior body 51 . In addition to the positive electrode 11a and the negative electrode 11b, an electrolytic solution (not shown) is sealed in the region surrounded by the outer package 51. As shown in FIG.

The positive electrode 11a and the negative electrode 11b of the battery 50 will be described with reference to FIG. FIG. 20A is a perspective view for explaining the stacking order of the positive electrode 11a, the negative electrode 11b, and the separator 14. FIG. FIG. 20B is a perspective view showing lead 12a and lead 12b in addition to positive electrode 11a and negative electrode 11b.

As shown in FIG. 20A, the battery 50 has a plurality of strip-shaped positive electrodes 11 a, a plurality of strip-shaped negative electrodes 11 b, and a plurality of separators 14 . The positive electrode 11a and the negative electrode 11b each have a projecting tab portion and a portion other than the tab. A positive electrode active material layer is formed on the portion other than the tab on one surface of the positive electrode 11a, and a negative electrode active material layer is formed on the portion other than the tab on one surface of the negative electrode 11b.

The positive electrode 11a and the negative electrode 11b are laminated such that the surfaces of the positive electrode 11a on which the positive electrode active material layer is not formed and the surfaces of the negative electrode 11b on which the negative electrode active material is not formed are in contact with each other.

A separator 14 is provided between the surface of the positive electrode 11a on which the positive electrode active material is formed and the surface of the negative electrode 11b on which the negative electrode active material is formed. Separator 14 is shown in FIG. 20 for clarity.
is indicated by a dotted line.

Further, as shown in FIG. 20B, the plurality of positive electrodes 11a and leads 12a are electrically connected at joints 15a. Also, the plurality of negative electrodes 11b and the leads 12b are electrically connected at the joints 15b.

Next, the exterior body 51 will be described with reference to FIGS. 19B1, 19B2, 19C, and 19D.

The exterior body 51 has a film-like shape, and is divided into two layers so as to sandwich the positive electrode 11a and the negative electrode 11b.
folded in half. The exterior body 51 has a bent portion 61 , a pair of seal portions 62 and a seal portion 63 . The pair of seal portions 62 are provided to sandwich the positive electrode 11a and the negative electrode 11b, and can also be called side seals. Moreover, the seal portion 63 has portions overlapping with the leads 12a and 12b, and can also be called a top seal.

The exterior body 51 preferably has a wavy shape in which ridge lines 71 and valley lines 72 are alternately arranged in portions overlapping the positive electrode 11a and the negative electrode 11b. Moreover, the sealing portion 62 and the sealing portion 63 of the exterior body 51 are preferably flat.

FIG. 19(B1) is a cross section cut at a portion overlapping with the ridgeline 71, and FIG. 19(B2) is
This is a cross section cut at a portion overlapping the valley line 72 . Both FIGS. 19(B1) and (B2) show the battery 5
0 and cross sections of the positive electrode 11a and the negative electrode 11b in the width direction.

Here, the distance between the ends of the positive electrode 11a and the negative electrode 11b in the width direction, ie, the ends of the positive electrode 11a and the negative electrode 11b, and the seal portion 62 is defined as a distance La. When deformation such as bending is applied to the battery 50, the positive electrode 11a and the negative electrode 11b are deformed so as to be displaced from each other in the length direction as described later. At that time, if the distance La is too short, the exterior body 51 may be strongly rubbed against the positive electrode 11a and the negative electrode 11b, and the exterior body 51 may be damaged. In particular, when the metal film of the exterior body 51 is exposed, the metal film may be corroded by the electrolytic solution. Therefore, it is preferable to set the distance La as long as possible. On the other hand, if the distance La is too large, the volume of the battery 50 will increase.

In addition, it is preferable to increase the distance La between the positive electrode 11a and the negative electrode 11b and the seal portion 62 as the total thickness of the stacked positive electrode 11a and negative electrode 11b increases.

More specifically, when the total thickness of the laminated positive electrode 11a and negative electrode 11b and the separator 214 (not shown) is the thickness t, and the total thickness of the laminated layers is the thickness t, the distance La
is 0.8 to 3.0 times the thickness t, preferably 0.9 to 2.5 times, more preferably 1.0 to 2.0 times the thickness t. By setting the distance La within this range, a compact battery with high reliability against bending can be realized.

Further, when the distance between the pair of seal portions 62 is Lb, it is preferable to make the distance Lb sufficiently larger than the width of the positive electrode 11a and the negative electrode 11b (here, the width Wb of the negative electrode 11b). As a result, even if the positive electrode 11a and the negative electrode 11b come into contact with the exterior body 51 when the battery 50 is subjected to deformation such as repeated bending, part of the positive electrode 11a and the negative electrode 11b can be displaced in the width direction. , it is possible to effectively prevent the positive electrode 11a and the negative electrode 11b from being rubbed against the exterior body 51 .

For example, the difference between the distance La between the pair of seal portions 62 and the width Wb of the negative electrode 11b is the positive electrode 1
1.6 to 6.0 times, preferably 1.8 to 5 times the thickness t of 1a and negative electrode 11b
. It is preferable to satisfy 0 times or less, more preferably 2.0 times or more and 4.0 times or less.

In other words, it is preferable that the distance Lb, the width Wb, and the thickness t satisfy the relationship of Equation 1 below.

Here, a satisfies 0.8 or more and 3.0 or less, preferably 0.9 or more and 2.5 or less, more preferably 1.0 or more and 2.0 or less.

FIG. 19C is a cross section including the lead 12a, and corresponds to cross sections in the longitudinal direction of the battery 50, the positive electrode 11a and the negative electrode 11b. As shown in FIG. 19(C) , it is preferable to have a space 73 between the ends of the positive electrode 11 a and the negative electrode 11 b in the length direction and the exterior body 51 in the bent portion 61 .

FIG. 19D shows a schematic cross-sectional view when the battery 50 is bent. FIG. 19(D) shows
This corresponds to the cross section taken along the cutting line B1-B2 in FIG. 19(A).

When the battery 50 is bent, a portion of the exterior body 51 positioned outside the bend is elongated, and the other portion positioned inside is contracted. More specifically, the portion located outside the exterior body 51 is
The wave is deformed so that the amplitude of the wave is small and the period of the wave is large. On the other hand, the portion positioned inside the exterior body 51 deforms such that the amplitude of the waves is large and the cycle of the waves is small. In this way, the deformation of the exterior body 51 relieves the stress applied to the exterior body 51 due to bending, so that the material itself forming the exterior body 51 does not need to expand and contract. As a result, the exterior body 5
1 can bend the battery 50 with a small force without breaking.

Further, as shown in FIG. 19D, when the battery 50 is bent, the positive electrode 11a and the negative electrode 11b
and shift relative to each other. At this time, the plurality of stacked positive electrodes 11a and negative electrodes 11b
Since one end on the sealing portion 63 side is fixed by the fixing member 17 , they are displaced so that the amount of displacement increases as they are closer to the bent portion 61 . As a result, the positive electrode 11a and the negative electrode 1
The stress applied to 1b is relaxed, and the positive electrode 11a and the negative electrode 11b themselves do not need to expand and contract.
As a result, the battery 50 can be bent without damaging the positive electrode 11a and the negative electrode 11b.

In addition, since the space 73 is provided between the positive electrode 11a and the negative electrode 11b and the outer package 51, the positive electrode 11a and the negative electrode 11b positioned inside when the outer package 51 is bent does not come into contact with the outer package 51. can deviate.

The battery 50 exemplified in FIGS. 19 and 20 is a battery in which damage to the exterior body, damage to the positive electrode 11a and the negative electrode 11b, and the like are unlikely to occur even when repeatedly bent and stretched, and battery characteristics are also unlikely to deteriorate. By using the positive electrode active material described in the previous embodiment for the positive electrode 11a of the battery 50, the battery can have even better cycle characteristics.

(Embodiment 5)
In this embodiment, an example of mounting a secondary battery, which is one embodiment of the present invention, in an electronic device will be described.

First, FIGS. 21A to 21G show an example of mounting the bendable secondary battery, which is described in part of Embodiment 3, in an electronic device. As an electronic device to which a bendable secondary battery is applied, for example, a television device (also called television or television receiver)
, monitors for computers, etc., digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones and mobile phone devices), mobile game machines, mobile information terminals, audio playback devices, large games such as pachinko machines machines, etc.

It is also possible to incorporate a secondary battery having a flexible shape along the inner wall or outer wall of a house or building, or along the curved surface of the interior or exterior of an automobile.

FIG. 21A shows an example of a mobile phone. A mobile phone 7400 includes a housing 740
1, an operation button 7403, an external connection port 7404,
A speaker 7405, a microphone 7406, and the like are provided. Note that the mobile phone 7400 has a secondary battery 7407 . By using the secondary battery of one embodiment of the present invention as the secondary battery 7407, a lightweight mobile phone with a long life can be provided.

FIG. 21B shows a state in which the mobile phone 7400 is bent. mobile phone 74
00 is deformed by an external force to bend the whole, the secondary battery 7407 provided therein is also bent. The state of the bent secondary battery 7407 at that time is shown in FIG.
C). A secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in a bent state. Note that the secondary battery 7407 has a lead electrode 7408 electrically connected to the current collector 7409 . For example, the current collector 7409 is a copper foil, which is partly alloyed with gallium to improve adhesion between the current collector 7409 and the active material layer in contact with the secondary battery 7407 .
It has a highly reliable configuration in a bent state.

FIG. 21D illustrates an example of a bangle-type display device. A portable display device 7100 includes a housing 7101 , a display portion 7102 , operation buttons 7103 , and a secondary battery 7104 . FIG. 21E shows the state of the secondary battery 7104 that is bent. When the secondary battery 7104 is worn on a user's arm in a bent state, the housing is deformed and the curvature of part or all of the secondary battery 7104 changes. The radius of curvature represents the degree of curvature at an arbitrary point of the curve by the value of the radius of the corresponding circle, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or all of the main surface of the housing or the secondary battery 7104 changes within the range of radius of curvature of 40 mm or more and 150 mm or less. The radius of curvature of the main surface of the secondary battery 7104 is 40 mm or more 15
High reliability can be maintained within the range of 0 mm or less. By using the secondary battery of one embodiment of the present invention for the secondary battery 7104, a lightweight and long-life portable display device can be provided.

FIG. 21F shows an example of a wristwatch-type portable information terminal. Portable information terminal 7200
, a housing 7201, a display unit 7202, a band 7203, a buckle 7204, and operation buttons 7
205, an input/output terminal 7206, and the like.

Personal digital assistant 7200 is capable of running a variety of applications such as mobile phones, e-mail, text viewing and composition, music playback, Internet communication, computer games, and the like.

The display portion 7202 has a curved display surface, and can perform display along the curved display surface. The display portion 7202 includes a touch sensor and can be operated by touching the screen with a finger, a stylus, or the like. For example, icon 7 displayed on the display unit 7202
An application can be launched by touching 207 .

The operation button 7205 can have various functions such as time setting, power on/off operation, wireless communication on/off operation, manner mode execution/cancellation, and power saving mode execution/cancellation. . For example, an operating system installed in the mobile information terminal 7200 can freely set the functions of the operation buttons 7205 .

In addition, the mobile information terminal 7200 is capable of performing short-range wireless communication according to communication standards. For example, by intercommunicating with a headset capable of wireless communication, hands-free communication is also possible.

In addition, the portable information terminal 7200 has an input/output terminal 7206 and can directly exchange data with another information terminal through a connector. Also, charging can be performed through the input/output terminal 7206 . Note that the charging operation may be performed by wireless power supply without using the input/output terminal 7206 .

The display portion 7202 of the portable information terminal 7200 includes the secondary battery of one embodiment of the present invention. By using the secondary battery of one embodiment of the present invention, a portable information terminal that is lightweight and has a long life can be provided. For example, the secondary battery 7104 shown in FIG. 21E can be incorporated in the housing 7201 in a curved state or in the band 7203 in a curved state.

Personal digital assistant 7200 preferably has a sensor. As sensors, for example, it is preferable to mount a human body sensor such as a fingerprint sensor, a pulse sensor, a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, and the like.

FIG. 21G illustrates an example of an armband-type display device. The display device 7300 includes a display portion 7304 and a secondary battery of one embodiment of the present invention. Moreover, the display device 7300
A touch sensor can be provided in the display portion 7304, and the display portion 7304 can function as a portable information terminal.

The display surface of the display portion 7304 is curved, and display can be performed along the curved display surface. In addition, the display device 7300 can change the display state by short-range wireless communication or the like according to communication standards.

In addition, the display device 7300 has an input/output terminal and can directly exchange data with another information terminal through a connector. Also, charging can be performed via the input/output terminals. Note that the charging operation may be performed by wireless power supply without using the input/output terminal.

By using the secondary battery of one embodiment of the present invention as the secondary battery included in the display device 7300,
A display device that is lightweight and has a long life can be provided.

An example of mounting the secondary battery with good cycle characteristics described in the above embodiment in an electronic device will be described with reference to FIGS.

By using the secondary battery of one embodiment of the present invention as a secondary battery in a daily electronic device, a product that is lightweight and has a long life can be provided. For example, as electronic devices for daily use, electric toothbrushes, electric shavers,
Electric beauty equipment and the like can be mentioned, and secondary batteries for these products are desired to be stick-shaped, compact, lightweight, and large-capacity secondary batteries in consideration of the user's ease of holding. .

FIG. 21(H) is a perspective view of a device also called a cigarette containing smoking device (electronic cigarette).
In FIG. 21(H), an electronic cigarette 7500 is composed of an atomizer 7501 including a heating element, a secondary battery 7504 for supplying power to the atomizer, and a cartridge 7502 including a liquid supply bottle, sensor, and the like. In order to improve safety, a protection circuit for preventing overcharge and overdischarge of the secondary battery 7504 may be electrically connected to the secondary battery 7504 . A secondary battery 7504 shown in FIG. 22H has an external terminal so that it can be connected to a charging device. Since the secondary battery 7504 becomes a tip portion when held, it is desirable that the total length be short and the weight be light. Since the secondary battery of one embodiment of the present invention has high capacity and favorable cycle characteristics, the electronic cigarette 7500 that is small and lightweight and can be used for a long time can be provided.

Next, FIGS. 22A and 22B show an example of a tablet terminal that can be folded in half. A tablet terminal 9600 shown in FIGS. 22A and 22B includes a housing 963
0a, housing 9630b, movable unit 9640 connecting housing 9630a and housing 9630b, display unit 9631 having display units 9631a and 9631b, display mode switching switch 9626, power switch 9627, power saving mode switching switch 9625, fastener 9
629, and an operation switch 9628. By using a flexible panel for the display portion 9631, the tablet terminal can have a wider display portion. Figure 22 (
A) shows a state in which the tablet terminal 9600 is opened, and FIG. 22B shows a state in which the tablet terminal 9600 is closed.

The tablet terminal 9600 also includes a power storage unit 9635 inside the housings 9630a and 9630b. The power storage unit 9635 is provided across the housing 9630a and the housing 9630b through the movable portion 9640.

Part of the display portion 9631a can be a touch panel region 9632a, and data can be input by touching a displayed operation key 9638 . Note that the display unit 96
In 31a, as an example, a configuration in which half of the area has only a display function and a configuration in which the other half of the area has a touch panel function is shown, but the configuration is not limited to this. Display unit 96
The entire area of 31a may have a touch panel function. For example, the display unit 9
The entire surface of 631a can be used as a touch panel by displaying keyboard buttons, and the display portion 9631b can be used as a display screen.

Further, in the display portion 9631b, part of the display portion 9631b can be used as a touch panel region 9632b, similarly to the display portion 9631a. Further, a keyboard button can be displayed on the display portion 9631b by touching a position where the keyboard display switching button 9639 of the touch panel is displayed with a finger, a stylus, or the like.

Further, touch input can be performed simultaneously on the touch panel region 9632a and the touch panel region 9632b.

A display mode switching switch 9626 can switch the orientation of display such as vertical display or horizontal display, and can select switching between black-and-white display and color display. The power saving mode switching switch 9625 can optimize display luminance according to the amount of external light during use detected by a light sensor incorporated in the tablet terminal 9600 . The tablet terminal may incorporate not only the optical sensor but also other detection devices such as a sensor for detecting inclination such as a gyro and an acceleration sensor.

In addition, FIG. 22A shows an example in which the display areas of the display portion 9631b and the display portion 9631a are the same; however, there is no particular limitation. can be different. For example, one of them may be a display panel capable of displaying with higher definition than the other.

FIG. 22B shows a closed state, and the tablet terminal includes a housing 9630, a solar cell 9
633 has a charge/discharge control circuit 9634 including a DCDC converter 9636 . As the power storage unit 9635, the power storage unit of one embodiment of the present invention is used.

Note that since the tablet terminal 9600 can be folded in half, it can be folded so that the housings 9630a and 9630b overlap each other when not in use. Since the display portions 9631a and 9631b can be protected by folding, the durability of the tablet terminal 9600 can be increased. Further, a power storage unit 9635 using the secondary battery of one embodiment of the present invention
has high capacity and good cycle characteristics, it is possible to provide the tablet terminal 9600 that can be used for a long time.

In addition, the tablet terminals shown in FIGS. 22(A) and 22(B) have a function of displaying various information (still images, moving images, text images, etc.), a calendar, a date or time, and the like. It can have a function of displaying on the display unit, a touch input function of performing a touch input operation or editing information displayed on the display unit, a function of controlling processing by various software (programs), and the like.

A solar cell 9633 attached to the surface of the tablet terminal can supply power to a touch panel, a display portion, a video signal processing portion, or the like. Note that the solar cell 9633
It can be provided on one side or both sides of the housing 9630, so that the power storage unit 9635 can be charged efficiently. Note that using a lithium-ion secondary battery as the power storage unit 9635 has an advantage such as miniaturization.

Also, the configuration and operation of the charge/discharge control circuit 9634 shown in FIG.
A block diagram is shown in (C) and explained. In FIG. 22C, a solar cell 9633 and a power storage body 96
35, DCDC converter 9636, converter 9637, switches SW1 to SW3,
A display portion 9631 is shown, and a power storage unit 9635, a DCDC converter 9636, a converter 9637, and switches SW1 to SW3 are included in the charge/discharge control circuit 9 shown in FIG.
634.

First, an example of operation in the case where the solar cell 9633 generates power with external light is described. The power generated by the solar cell is DCDC so that it becomes a voltage for charging the power storage body 9635
Converter 9636 steps up or down. Then, when the power from the solar cell 9633 is used for the operation of the display unit 9631, the switch SW1 is turned on, and the converter 963
7, the voltage required for the display unit 9631 is increased or decreased. Also, the display unit 963
When 1 is not displayed, the power storage unit 9635 may be charged by turning off SW1 and turning on SW2.

Although the solar cell 9633 is shown as an example of power generation means, it is not particularly limited.
A configuration in which the power storage body 9635 is charged by other power generating means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element) may be employed. For example, a non-contact power transmission module that transmits and receives power wirelessly (non-contact) for charging may be used in combination with other charging means.

FIG. 23 shows an example of another electronic device. In FIG. 23, a display device 8000 is an example of an electronic device using a secondary battery 8004 of one embodiment of the present invention. Specifically, the display device 80
00 corresponds to a display device for receiving TV broadcast, and includes a housing 8001, a display portion 8002, a speaker portion 8003, a secondary battery 8004, and the like. A secondary battery 8004 according to one embodiment of the present invention includes
It is provided inside the housing 8001 . The display device 8000 can receive power from a commercial power source or can use power accumulated in the secondary battery 8004 . Therefore, the use of the secondary battery 8004 according to one embodiment of the present invention as an uninterruptible power supply makes it possible to use the display device 8000 even when power cannot be supplied from a commercial power supply due to a power failure or the like.

The display portion 8002 includes a liquid crystal display device, a light emitting device in which each pixel is provided with a light emitting element such as an organic EL element, an electrophoretic display device, a DMD (Digital Micromirror Device).
ice), PDP (Plasma Display Panel), FED (Field
A semiconductor display device such as an emission display) can be used.

The display device includes all display devices for information display, such as for TV broadcast reception, personal computer, advertisement display, and the like.

In FIG. 23, a stationary lighting device 8100 includes a secondary battery 8 according to one embodiment of the present invention.
1 is an example of an electronic device using 103. FIG. Specifically, the lighting device 8100 includes a housing 8101,
It has a light source 8102, a secondary battery 8103, and the like. In FIG. 23, the secondary battery 8103 is
101 and the light source 8102 are installed inside the ceiling 8104 , but the secondary battery 8103 may be installed inside the housing 8101 . The lighting device 8100 can receive power from a commercial power source or can use power accumulated in the secondary battery 8103 . Therefore, the use of the secondary battery 8103 according to one embodiment of the present invention as an uninterruptible power supply makes it possible to use the lighting device 8100 even when power cannot be supplied from a commercial power supply due to a power failure or the like.

Note that although FIG. 23 illustrates the stationary lighting device 8100 provided on the ceiling 8104, the secondary battery according to one embodiment of the present invention can be used in places other than the ceiling 8104, such as the sidewalls 8105, the floor 8106, and the windows 8107. It can also be used for a stationary lighting device provided in a desk, or for a desk-top lighting device.

For the light source 8102, an artificial light source that artificially obtains light using electric power can be used. Specifically, incandescent lamps, discharge lamps such as fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements are examples of the artificial light sources.

An air conditioner including an indoor unit 8200 and an outdoor unit 8204 in FIG. 23 is an example of an electronic device using a secondary battery 8203 according to one embodiment of the present invention. Specifically, the indoor unit 8200 has a housing 8201, a blower port 8202, a secondary battery 8203, and the like. Figure 23
Although the case where the secondary battery 8203 is provided in the indoor unit 8200 is illustrated here, the secondary battery 8203 may be provided in the outdoor unit 8204 . Alternatively, both the indoor unit 8200 and the outdoor unit 8204 may be provided with the secondary battery 8203 . The air conditioner can receive power from a commercial power source or can use power accumulated in the secondary battery 8203 . In particular, the secondary battery 8 is installed in both the indoor unit 8200 and the outdoor unit 8204.
203, the air conditioner can be used by using the secondary battery 8203 according to one embodiment of the present invention as an uninterruptible power supply even when power cannot be supplied from a commercial power supply due to a power failure or the like. becomes.

Note that FIG. 23 exemplifies a separate type air conditioner composed of an indoor unit and an outdoor unit, but an integrated type air conditioner having the function of the indoor unit and the function of the outdoor unit in one housing is used. , the secondary battery according to one embodiment of the present invention can also be used.

In FIG. 23, an electric refrigerator-freezer 8300 includes a secondary battery 8304 according to one embodiment of the present invention.
It is an example of an electronic device using Specifically, the electric refrigerator-freezer 8300 includes a housing 8301,
It has a refrigerator compartment door 8302, a freezer compartment door 8303, a secondary battery 8304, and the like. In Figure 23,
A secondary battery 8304 is provided inside the housing 8301 . The electric refrigerator-freezer 8300 can receive power from a commercial power source, or can use power stored in a secondary battery 8304 . Therefore, the electric refrigerator-freezer 8300 can be used by using the secondary battery 8304 according to one embodiment of the present invention as an uninterruptible power supply even when power cannot be supplied from a commercial power supply due to a power failure or the like.

Among the electronic devices described above, high-frequency heating devices such as microwave ovens and electronic devices such as electric rice cookers require high power in a short period of time. Therefore, by using the secondary battery according to one embodiment of the present invention as an auxiliary power supply for supplementing electric power that cannot be covered by the commercial power supply, it is possible to prevent the breaker of the commercial power supply from tripping when the electronic device is in use. .

In addition, during times when electronic equipment is not used, especially during times when the ratio of the amount of power actually used to the total power that can be supplied by commercial power supply sources (called the power usage rate) is low, By storing electric power in the secondary battery, it is possible to suppress an increase in the electric power usage rate during periods other than the above time period. For example, in the case of the electric freezer-refrigerator 8300, the temperature is low and the refrigerator compartment door 83 is closed.
02, power is stored in the secondary battery 8304 at night when the freezer compartment door 8303 is not opened and closed. In the daytime when the temperature rises and the refrigerator compartment door 8302 and the freezer compartment door 8303 are opened and closed, the secondary battery 8304 is used as an auxiliary power supply, so that the power usage rate during the daytime can be kept low.

According to one embodiment of the present invention, the secondary battery can have favorable cycle characteristics and improved reliability. In addition, according to one aspect of the present invention, a high-capacity secondary battery can be obtained, so that the characteristics of the secondary battery can be improved, and thus the size and weight of the secondary battery itself can be reduced. can. Therefore, by including the secondary battery which is one embodiment of the present invention in the electronic device described in this embodiment, the electronic device can have a longer life and a lighter weight. This embodiment can be implemented in appropriate combination with other embodiments.

(Embodiment 6)
In this embodiment, an example in which a vehicle is equipped with a secondary battery that is one embodiment of the present invention will be described.

By installing a secondary battery in a vehicle, a next-generation clean energy vehicle such as a hybrid vehicle (HEV), an electric vehicle (EV), or a plug-in hybrid vehicle (PHEV) can be realized.

FIG. 24 illustrates a vehicle using a secondary battery that is one embodiment of the present invention. Figure 24 (A
) is an electric vehicle that uses an electric motor as a power source for running. Alternatively, it is a hybrid vehicle in which an electric motor and an engine can be appropriately selected and used as power sources for running. By using one aspect of the present invention, a vehicle with a long cruising range can be realized. Also, automobile 8400 has a secondary battery. As for the secondary battery, the secondary battery modules shown in FIGS. 7(C) and 7(D) may be arranged side by side on the floor of the vehicle. Also, a battery pack formed by combining a plurality of secondary batteries shown in FIG. 12 may be installed on the floor of the vehicle. The secondary battery can not only drive the electric motor 8406 but also supply power to light emitting devices such as the headlight 8401 and room lights (not shown).

In addition, the secondary battery can supply power to display devices such as a speedometer and a tachometer of the automobile 8400 . In addition, the secondary battery can supply power to a semiconductor device such as a navigation system included in the automobile 8400 .

A vehicle 8500 shown in FIG. 24B can be charged by receiving power from an external charging facility by a plug-in method, a contactless power supply method, or the like to a secondary battery included in the vehicle 8500 . FIG. 24B shows a state in which a secondary battery 8024 mounted on an automobile 8500 is charged via a cable 8022 from a charging device 8021 installed on the ground. When charging, the charging method, the standard of the connector, etc. may be appropriately performed by a predetermined method such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station provided in a commercial facility, or may be a household power source. For example, plug-in technology can charge the secondary battery 8024 mounted on the automobile 8500 with power supplied from the outside. Charging can be performed by converting AC power into DC power via a conversion device such as an ACDC converter.

Also, although not shown, the power receiving device can be mounted on a vehicle, and power can be supplied from a power transmission device on the ground in a non-contact manner for charging. In the case of this non-contact power supply system, it is possible to charge the battery not only while the vehicle is stopped but also while the vehicle is running by installing a power transmission device on the road or on the outer wall. In addition, electric power may be transmitted and received between vehicles using this contactless power supply method. Furthermore, a solar battery may be provided on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped or running. An electromagnetic induction method or a magnetic resonance method can be used for such contactless power supply.

FIG. 24C illustrates an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. Figure 2
A scooter 8600 shown in 4(C) includes a secondary battery 8602 , a side mirror 8601 and a direction indicator light 8603 . A secondary battery 8602 can supply electricity to the turn signal lights 8603 .

Also, the scooter 8600 shown in FIG.
02 can be accommodated. The secondary battery 8602 can be stored in the underseat storage 8604 even if the underseat storage 8604 is small. The secondary battery 8602 is removable, and when charging, the secondary battery 8602 can be carried indoors, charged, and stored before traveling.

According to one embodiment of the present invention, the cycle characteristics of the secondary battery are improved, and the capacity of the secondary battery can be increased. Therefore, the size and weight of the secondary battery itself can be reduced. If the size and weight of the secondary battery itself can be reduced, the cruising distance can be improved because it contributes to the weight reduction of the vehicle. A secondary battery mounted on a vehicle can also be used as a power supply source other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand. If it is possible to avoid using a commercial power supply during peak power demand, it can contribute to energy conservation and reduction of carbon dioxide emissions. Moreover, if the cycle characteristics are good, the secondary battery can be used for a long period of time, so the amount of rare metals such as cobalt used can be reduced.

This embodiment can be implemented in appropriate combination with other embodiments.

In this example, a positive electrode active material that is one embodiment of the present invention and a positive electrode active material that is a comparative example were prepared.
Features were analyzed using RD. In addition, the cycle characteristics in high voltage charging were evaluated.

[Preparation of positive electrode active material]
≪Sample 1≫
In Sample 1, a positive electrode active material containing cobalt as a transition metal was manufactured by the manufacturing method shown in FIGS. First, the molar ratio of LiF and _MgF2 is LiF: _MgF2
= 1:3, acetone was added as a solvent, and wet-mixed and pulverized.
Mixing and pulverization were performed with a ball mill using zirconia balls at 150 rpm for 1 hour. The post-treatment material was collected and used as a first mixture.

In Sample 1, nickel-manganese-lithium cobaltate manufactured by Toyoshima Seisakusho Co., Ltd. was used as a pre-synthesized composite oxide. Nickel-manganese-lithium cobaltate is nickel-manganese-lithium cobaltate having an average particle size (D50) of about 12 μm. When the nickel-manganese-lithium cobaltate was measured using SEM-EDX, the atomic ratio of nickel, manganese and cobalt was nickel:manganese:cobalt=1:
1.8:1.2. In addition, the atomic number ratio calculated the average value of a total of 5 measurement points.

Next, the first mixture was weighed so that the atomic weight of magnesium contained in the first mixture was 0.5 atomic % with respect to the molecular weight of nickel-manganese-lithium cobaltate, and dry-mixed. Mixing was performed with a ball mill using zirconia balls at 150 rpm for 1 hour. The post-treatment material was collected and used as a second mixture.

Next, the second mixture was placed in an alumina crucible and placed in a muffle furnace in an oxygen atmosphere at 700° C. for 6 hours.
Annealed for 0 hours. The flow rate of oxygen was 10 L/min. The temperature is raised at 200°C/hr,
The temperature was lowered over 10 hours or more. The material after the heat treatment was used as the positive electrode active material of Sample 1.

≪Sample 2≫
In Sample 2, nickel-manganese-lithium cobaltate was not mixed with the first mixture, but only annealed. Annealing conditions were the same as in Sample 1.

≪Sample 3≫
Nickel-manganese-lithium cobaltate without any particular treatment was used as Sample 3 (comparative example).

[Production of secondary battery]
Next, a coin-type secondary battery of CR2032 type (diameter: 20 mm, height: 3.2 mm) was manufactured using Sample 1 to Sample 3 manufactured above.

For the positive electrode, a slurry obtained by mixing the positive electrode active material prepared above, acetylene black (AB), and polyvinylidene fluoride (PVDF) in an active material:AB:PVDF=95:3:2 (weight ratio) was collected. A material coated on an electric body was used.

Lithium metal was used as the counter electrode.

1 mol/L lithium hexafluorophosphate (LiPF ₆ ) is used as the electrolyte in the electrolytic solution, and the electrolytic solution contains ethylene carbonate (EC) and diethyl carbonate (DEC) in a ratio of EC:DEC=3:7 ( volume ratio) and vinylene carbonate (VC) mixed at 2 wt %.

Polypropylene having a thickness of 25 μm was used for the separator.

The cathode can and the anode can were made of stainless steel (SUS).

The positive electrodes of the secondary batteries using Sample 1 to Sample 3 were pressurized at 210 kN.

[Calculation of lattice constant from XRD before charging]
Powder XRD analysis using CuKα1 rays was performed on the positive electrodes of Sample 1 and Sample 3 before charging. XRD was measured in air, and the electrodes were attached to a glass plate to maintain flatness. The XRD apparatus was set up for powder samples, but the height of the sample was matched to the required measurement plane of the apparatus.

The obtained XRD pattern is shown in FIG. 25(A). The XRD pattern obtained is DIFF
RAC. Background removal and Kα2 removal were performed using EVA (Bruker XRD data analysis software). As a result, signals derived from the carbon of the conductive aid and binder, and the sealed container are also removed.

[XRD after initial charge (1st charge)]
Secondary batteries using Sample 1 and Sample 3 were CCCV charged at 4.6V. Specifically, after constant current charging at 0.5C with 4.6V as the upper limit, the current value is 0.01C.
Constant voltage charging was carried out until 1C is a current value per positive electrode active material of 137 mA/g.
Then, the secondary battery in a charged state was dismantled in an argon atmosphere glove box, the positive electrode was taken out, and the positive electrode was washed with DMC (dimethyl carbonate) to remove the electrolyte. Then, it was sealed in a sealed container in an argon atmosphere and subjected to XRD analysis.

FIG. 25B shows XRD patterns of positive electrodes after secondary batteries using Sample 1 and Sample 3 were charged at 4.6 V. FIG. Also, in FIG. 25B, 2θ=18.
An enlarged view near 5° is shown in FIG. 26A, and an enlarged view near 2θ=37.0° is shown in FIG.
B) and an enlarged view near 2θ=37.0° are shown in FIG. 2θ=1
Both the peak near 8.5° and the peak near 2θ=45.0° were broad peaks. As mentioned above, the peak near 18.5° and the peak near 45.0° are 37.
Compared to the peak near 0°, it is considered to be more susceptible to expansion and contraction of the c-axis. These peaks broadened upon charging, suggesting expansion and contraction of the c-axis. Also, for example, FIG.
The spectrum shown in 7(A) suggests separation into two peaks. Therefore, Sampl
It is suggested that e1 and Sample3 may have two phases.

[XRD after initial discharge (1st discharge)]
Secondary batteries using Sample 1 and Sample 3 were CCCV-charged at 4.6V and then CC-discharged at 2.5V. Specifically, after constant current charging at 0.5 C with an upper limit of 4.6 V, constant voltage charging is performed until the current value reaches 0.01 C, and then 0.5 V with a lower limit of 2.5 V.
Constant current discharge was performed at 5C. 1C is a current value per positive electrode active material of 137 mA/g. Then, the secondary battery in a charged state was dismantled in an argon atmosphere glove box, the positive electrode was taken out, and the positive electrode was washed with DMC (dimethyl carbonate) to remove the electrolyte. Then, it was sealed in a sealed container in an argon atmosphere and subjected to XRD analysis.

FIG. 27B shows the XRD patterns of the positive electrodes after charging the secondary batteries using Sample 1 and Sample 3 at 4.6V. FIG. 28 also shows charge and discharge curves.

[XRD after second charge (2nd charge)]
The secondary batteries using Sample 1 and Sample 3 were charged/discharged once under the same conditions as the initial charge/discharge, then charged for the second time, and then subjected to XRD analysis.

Lattice constants were calculated using TOPAS for the measured XRD patterns. At this time, optimization of atomic positions and the like was not performed, and only lattice constants were fitted. GOF (good
of fitness), the estimated crystallite size, the lattice constants of the a-axis and c-axis, the value obtained by dividing the a-axis by the c-axis (a/c), and the respective proportions in the case of having multiple phases are shown in Table 1 and Table 2 shows. Table 1 shows the analysis results of Sample 1, and Table 2 shows the analysis results of Sample 2, respectively. Moreover, the CRs listed in Tables 1 and 2 were normalized with the a/c of the first discharge being 1.

From Table 1, the average value of a/c in the first phase and the second phase after the initial charge of Sample 1 is 0.0.
In 1990, the average CR was 1.0000, the average a/c of the first and second phases after the second charge was 0.1989, and the average CR was 0.9999. From Table 2, Sample
The average value of a/c of the first phase and the second phase after the first charge of 3 is 0.1976, the average value of CR is 0.9921, and the first phase and the second phase after the second charge The average value of a/c is 0.1976, C
The average value of R was 0.9922. Sample 1 showed a CR value closer to 1, suggesting that the anisotropy of strain after discharge was suppressed.

[Cycle characteristics]
Next, FIG. 29 shows the result of evaluating the cycle characteristics of the secondary batteries using Sample 1 to Sample 3. FIG.

Charging and discharging were performed at 25°C. 1C is a current value per positive electrode active material of 137 mA/g.
The charging condition is CCCV (0.5C, 4.6V, final current 0.01C), and the discharging condition is CC (
0.5C, 2.5V) and discharge capacity after 50 cycles of charging and discharging. FIG. 29(A) shows the discharge capacity (Discha
Rge Capacity), and FIG. 29B shows the cycle number (Cycle nu
mber) of the discharge capacity (Capacity Retention Ra
te) are shown, respectively.

In Sample 3, which was suggested by XRD analysis results to suppress strain anisotropy in the process of charging and discharging, it was found that the decrease in capacity due to cycles was suppressed.

11a positive electrode 11b negative electrode 12a lead 12b lead 14 separator 15a joint 15b joint 17 fixing member 50 battery 51 exterior body 61 bent portion 62 sealing portion 63 sealing portion 71 ridge line 72 valley line 73 space 100 positive electrode active material 200 active material layer 201 graphene Compound 214 Separator 300 Secondary battery 301 Positive electrode can 302 Negative electrode can 303 Gasket 304 Positive electrode 305 Positive electrode current collector 306 Positive electrode active material layer 307 Negative electrode 308 Negative electrode current collector 309 Negative electrode active material layer 310 Separator 500 Secondary battery 501 Positive electrode current collector 502 Positive electrode active material layer 503 Positive electrode 504 Negative electrode current collector 505 Negative electrode active material layer 506 Negative electrode 507 Separator 508 Electrolytic solution 509 Case 510 Positive electrode lead electrode 511 Negative electrode lead electrode 600 Secondary battery 601 Positive electrode cap 602 Battery can 603 Positive electrode terminal 604 Positive electrode 605 separator 606 negative electrode 607 negative electrode terminal 608 insulating plate 609 insulating plate 611 PTC element 612 safety valve mechanism 613 conductive plate 614 conductive plate 615 module 616 conductive wire 617 temperature control device 900 circuit board 910 label 911 terminal 912 circuit 913 secondary battery 914 antenna 915 antenna 916 layer 917 layer 918 antenna 920 display device 921 sensor 922 terminal 930 housing 930a housing 930b housing 931 negative electrode 932 positive electrode 933 separator 950 wound body 951 terminal 952 terminal 980 secondary battery 981 film 982 film 993 wound body 994 negative electrode 995 positive electrode 996 separator 997 lead electrode 998 lead electrode 7100 portable display device 7101 housing 7102 display unit 7103 operation button 7104 secondary battery 7200 portable information terminal 7201 housing 7202 display unit 7203 band 7204 buckle 7205 operation button 7206 input/output terminal 7207 icon 7300 Display device 7304 Display unit 7400 Mobile phone 7401 Housing 7402 Display unit 7403 Operation button 7404 External connection port 7405 Speaker 7406 Microphone 7407 Secondary battery 7408 Lead electrode 7409 Current collector 7500 Electronic cigarette 7501 Atomizer 7502 Cartridge 7504 Secondary battery 8000 Display Device 8001 Housing 8002 Display 8003 Speaker 8004 Secondary battery 8021 Charging device 8022 Cable 8024 Secondary battery 8100 Lighting device 8101 Housing 8102 Light source 8103 Secondary battery 8104 Ceiling 8105 Side wall 8106 Floor 8107 Window 8200 Indoor unit 8201 Housing 8202 Air outlet 8203 Secondary battery 8204 Outdoor unit 8300 Electric refrigerator-freezer 8301 Housing Body 8302 Refrigerator compartment door 8303 Freezer compartment door 8304 Secondary battery 8400 Automobile 8401 Headlight 8406 Electric motor 8500 Automobile 8600 Scooter 8601 Side mirror 8602 Secondary battery 8603 Direction indicator light 8604 Storage under seat 9600 Tablet terminal 9625 Switch 9626 Switch 9627 Power switch 9628 Operation switch 9629 Fastener 9630 Housing 9630a Housing 9630b Housing 9631 Display unit 9631a Display unit 9631b Display unit 9632a Area 9632b Area 9633 Solar cell 9634 Charge/discharge control circuit 9635 Battery 9636 DCDC converter 9637 Converter 9638 Operation key 9639 button 9640 moving part

Claims (4)

having a positive electrode active material having a composite oxide containing lithium, nickel, manganese and cobalt;
The positive electrode active material has magnesium and halogen inside and on the surface,
the concentration of magnesium in the surface layer portion is higher than the concentration of magnesium in the inside;
the concentration of the halogen in the surface layer portion is higher than the concentration of the halogen in the interior;
In a battery using the positive electrode active material for the positive electrode and lithium metal for the negative electrode, constant current charging is performed until the battery voltage reaches 4.6 V, and then constant voltage charging. When the crystal structure of the positive electrode active material is represented by the space group R-3m, the value a_0/c_0 obtained by dividing the a-axis lattice constant by the c-axis lattice constant is greater than 0.198 and 0.202. smaller than
After discharging the battery at a constant current until the battery voltage reaches 2.5 V, the positive electrode is analyzed by powder X-ray diffraction using CuKα1 line, and the crystal structure of the positive electrode active material is represented by the space group R-3m. , a value obtained by dividing the a-axis lattice constant by the c-axis lattice constant is a_N/c_N, and the value of a_0/c_0 is more than 0.993 times and less than 1.02 times the a_N/c_N, secondary battery. having a positive electrode active material having a composite oxide containing lithium, nickel, manganese and cobalt;
The positive electrode active material has a region in which the atomic ratio of manganese is 0.5 to 2 times that of nickel,
The positive electrode active material has magnesium and halogen inside and on the surface,
the concentration of magnesium in the surface layer portion is higher than the concentration of magnesium in the inside;
the concentration of the halogen in the surface layer portion is higher than the concentration of the halogen in the interior;
In a battery using the positive electrode active material for the positive electrode and lithium metal for the negative electrode, constant current charging is performed until the battery voltage reaches 4.6 V, and then constant voltage charging. When the crystal structure of the positive electrode active material is represented by the space group R-3m, the value a_0/c_0 obtained by dividing the a-axis lattice constant by the c-axis lattice constant is greater than 0.198 and 0.202. smaller than
After discharging the battery at a constant current until the battery voltage reaches 2.5 V, the positive electrode is analyzed by powder X-ray diffraction using CuKα1 line, and the crystal structure of the positive electrode active material is represented by the space group R-3m. , a value obtained by dividing the a-axis lattice constant by the c-axis lattice constant is a_N/c_N, and the value of a_0/c_0 is more than 0.993 times and less than 1.02 times the a_N/c_N, secondary battery. In claim 1 or claim 2,
The lithium ion secondary battery, wherein the halogen is fluorine. In any one of claims 1 to 3,
When the positive electrode active material has a plurality of phases, and each of the plurality of phases has a crystal structure represented by the space group R-3m,
The value of a_0/c_0 is an average value of values obtained by dividing the a-axis lattice constant by the c-axis lattice constant in each of the plurality of phases.

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