JP2019179682A - Lithium ion secondary battery and method for manufacturing the same - Google Patents

Abstract

To provide a lithium ion secondary battery, high in energy density and good in cycle characteristics.SOLUTION: A lithium ion secondary battery includes: a positive electrode containing, as a positive electrode active material, a lithium-nickel composite oxide with a layered rock salt structure; a negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions; an electrolyte; and an exterior body. The lithium-nickel composite oxide is represented by composition formula: LiNiCoAlO(0.75≤x≤0.95, 0.03≤y≤0.20, 0.02≤z≤0.15, x+y+z=1), and a difference Δ2θ(λ=1.54 Å) between an H2 phase (003) peak position (2θ) in full charge and an H1 phase (003) peak position (2θ) in full discharge by an X-ray diffraction method is in the range from -0.3° to 0.3°.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery and a method for manufacturing the same.

  Lithium ion secondary batteries are widely used as power sources for small mobile devices such as mobile phones and laptop computers because of their high energy density and excellent charge / discharge cycle characteristics. Also, in recent years, due to consideration for environmental problems and increased awareness of energy saving, a large capacity and long life such as a storage battery for a vehicle such as an electric vehicle or a hybrid electric vehicle, and a power storage system such as a household power storage system are required. Demand for large power supplies is also increasing.

  Various studies have been made to improve the characteristics of lithium ion secondary batteries.

Patent Document 1 discloses a composition formula LiNi _{1-X in which} the peak intensity at an interplanar spacing of 4.72 ± 0.03 に 対 す る is 1.2 times or more of the peak intensity at an interplanar spacing of 2.03 ± 0.02 Å in X-ray analysis. A composite oxide given by M _X O ₂ (M is an element that can be a cation other than Ni that partially replaces Ni in LiNiO ₂ , 0 <X ≦ 0.5) as a positive electrode active material; A lithium battery containing lithium or a compound thereof as a negative electrode active material is described. The invention described in this patent document aims to solve the problem that the charge / discharge capacity of the high-voltage part is insufficient and the storage characteristics are poor, and to provide a lithium battery having a large charge / discharge energy and excellent storage characteristics. Yes.

Patent Document 2 includes a positive electrode using a composite oxide containing lithium as a positive electrode active material, a negative electrode using a carbonaceous material that can be doped / dedoped with lithium as a negative electrode active material, and a non-aqueous electrolyte. In the non-aqueous electrolyte secondary battery, the positive electrode active material is represented by Li _1-x Ni _y Co _1-y O ₂ (0.50 ≦ y ≦ 1.00), and the x value at the end of charging is A non-aqueous electrolyte secondary battery comprising a lithium / nickel / cobalt composite oxide set to 0.65 ≦ x ≦ 0.92 is described. An object of the invention described in this patent document is to provide a non-aqueous electrolyte secondary battery capable of obtaining excellent cycle characteristics while ensuring battery capacity and having a large accumulated energy until the end of its life. It is said.

In Patent Document 3, the composition formula LiMn _x Ni _1-x O ₂ (0.05 ≦ x ≦ 0.3), and the intensity I ₀₀₃ of the (003) plane diffraction line by powder X-ray diffraction method and ( positive electrode and the lithium capable of absorbing and desorbing carbon containing lithium composite oxide ratio _I 003 _{/ I 104} is 1.0 or more and 1.6 or less between the intensity _{I 104} of diffraction line 104) plane as the positive electrode active material A lithium secondary battery having a negative electrode including a material as a negative electrode active material is described. An object of the invention described in this patent document is to provide a lithium secondary battery having good cycle characteristics.

Patent Document 4 includes a positive electrode including a lithium nickel composite oxide having a layered rock salt structure as a positive electrode active material, a negative electrode including a negative electrode active material capable of occluding and releasing lithium ions, an electrolyte, and an exterior body. The nickel composite oxide is represented by a composition formula LiNi _x M _1-x O ₂ (x represents a value of 0.75 to ₁ , and M represents at least one metal element occupying nickel sites other than Ni), A lithium ion secondary battery is described that has a crystal phase with a face spacing d (003) greater than the face spacing d (003) during full discharge when fully charged. An object of the invention described in this patent document is to provide a lithium secondary battery having good input / output characteristics.

JP-A-6-215800 JP-A-7-320721 JP 2000-294240 A WO2017 / 082083

  However, further improvement is required for the cycle characteristics of the lithium ion secondary battery. Therefore, an object of the present invention is to provide a lithium ion secondary battery having a high energy density and good cycle characteristics.

According to one embodiment of the present invention, a positive electrode including a lithium nickel composite oxide having a layered rock salt structure as a positive electrode active material, a negative electrode including a negative electrode active material capable of occluding and releasing lithium ions, an electrolytic solution, and an exterior body are provided. Including
The lithium nickel composite oxide has a composition formula LiNi _x Co _y Al _z O ₂ (0.75 ≦ x ≦ 0.95, 0.03 ≦ y ≦ 0.20, 0.02 ≦ z ≦ 0.15, x + y + z = 1)
The difference Δ2θ (λ = 1.54Å) between the H2 phase (003) peak position (2θ) at the time of full charge and the H1 phase (003) peak position (2θ) at the time of complete discharge is −0.3 by the X-ray diffraction method. There is provided a lithium ion secondary battery characterized by being in the range of ° to 0.3 °.

According to another aspect of the present invention, a positive electrode including a lithium nickel composite oxide having a layered rock salt structure as a positive electrode active material, a negative electrode including a negative electrode active material capable of occluding and releasing lithium ions, an electrolyte, and an outer package A method for producing a lithium ion secondary battery comprising:
Forming a positive electrode;
Forming a negative electrode;
Containing the positive electrode, the negative electrode, and the electrolytic solution in the outer package;
The lithium nickel composite oxide has a composition formula LiNi _x Co _y Al _z O ₂ (0.75 ≦ x ≦ 0.95, 0.03 ≦ y ≦ 0.20, 0.02 ≦ z ≦ 0.15, x + y + z = 1)
The difference Δ2θ (λ = 1...) Between the H2 phase (003) peak position (2θ) when the lithium nickel composite oxide is fully charged and the H1 phase (003) peak position (2θ) when fully discharged by the X-ray diffraction method. 54Å) is set such that the upper limit charging voltage is in the range of −0.3 ° to 0.3 °, and a method of manufacturing a lithium ion secondary battery is provided.

  According to the embodiment of the present invention, it is possible to provide a lithium ion secondary battery having high energy density and good cycle characteristics.

It is sectional drawing for demonstrating an example of the lithium ion secondary battery by embodiment of this invention. It is a figure which shows the measurement result of In-situ XRD of the cell produced using lithium nickel complex oxide.

  A lithium ion secondary battery according to an embodiment of the present invention includes a positive electrode including a lithium nickel composite oxide having a layered rock salt structure as a positive electrode active material, a negative electrode including a negative electrode active material capable of occluding and releasing lithium ions, an electrolyte, Includes exterior body.

  In general, when the charging voltage is increased, the energy density is increased and the charging capacity can be improved. However, when the charging voltage is increased, the cycle characteristics tend to deteriorate. As a result of intensive investigations by paying attention to this problem, the present inventor has found that a secondary battery excellent in cycle characteristics can be obtained while securing a high energy density, and has completed the present invention.

That is, in the lithium ion secondary battery according to the embodiment of the present invention, one of the main features is that a lithium nickel composite oxide having a layered rock salt structure represented by the following composition formula is used as the positive electrode active material. .
LiNi _x Co _y Al _z O ₂
(0.75 ≦ x ≦ 0.95, 0.03 ≦ y ≦ 0.20, 0.02 ≦ z ≦ 0.15, x + y + z = 1)

  In this lithium nickel composite oxide, since the nickel content (x) is a high content of 0.75 or more, it contributes to higher energy density. In addition, the metal elements other than nickel occupying nickel sites are cobalt (Co) and aluminum (Al), and these contain at a ratio (y, z) in the above composition formula, thereby contributing to improvement of cycle characteristics. is doing. In the above composition formula, x, y, and z are preferably 0.75 ≦ x ≦ 0.90, 0.05 ≦ y ≦ 0.20, and 0.02 ≦ z ≦ 0.15, respectively. More preferably, .75 ≦ x ≦ 0.85, 0.10 ≦ y ≦ 0.20, and 0.02 ≦ z ≦ 0.10.

  Furthermore, the lithium ion secondary battery according to the embodiment of the present invention has, as one of main features, the H2 phase (003) peak position P2 (2θ) at the time of full charge and the H1 phase at the time of complete discharge by X-ray diffraction method. (003) The difference (P2−P1) = Δ2θ (λ = 1.54Å) from the peak position P1 (2θ) is in the range of −0.3 ° to 0.3 °. The crystal structure can be stabilized by making the c-axis lengths as close as possible during charging and discharging, and as a result, cycle characteristics can be improved. This difference Δ2θ is preferably in the range of −0.2 ° to 0.2 °, and more preferably in the range of −0.2 ° to 0.1 °.

In addition, the charging upper limit voltage of the lithium ion secondary battery according to the present embodiment is in the range of 4.25 to 4.45 V (vs. Li / Li ⁺ ) when the lithium nickel composite oxide represented by the above composition formula is used. Preferably, it is in the range of 4.25 to 4.4 V (vs. Li / Li ⁺ ), more preferably in the range of 4.25 to 4.35 V (vs. Li / Li ⁺ ). Further preferred. Having such a high charge upper limit voltage, combined with the high nickel content of the above composition formula, a high energy density can be realized.

In addition, the main feature of the method for manufacturing a lithium ion secondary battery according to the embodiment of the present invention is that a composition formula LiNi _x Co _y Al _z O ₂ (0.75 ≦ x ≦ 0.95, 0. 03 ≦ y ≦ 0.20, 0.02 ≦ z ≦ 0.15, x + y + z = 1), and at the time of full charge of the lithium nickel composite oxide by X-ray diffraction method The difference (P2-P1) = Δ2θ (λ = 1.54Å) between the H2 phase (003) peak position (2θ) and the H1 phase (003) peak position (2θ) during complete discharge is −0.3 ° to 0 The charging upper limit voltage is set to be within a range of 3 °. This charging upper limit voltage is preferably set so that Δ2θ is in the range of −0.2 ° to 0.2 °, and is set so that Δ2θ is in the range of −0.2 ° to 0.1 °. It is more preferable. Further, the charging upper limit voltage is preferably set in a range of 4.25~4.45V (vs.Li/Li ^+), set in the range of 4.25~4.4V (vs.Li/Li ⁺⁾ it is more preferable to, and more preferably set in a range of 4.25~4.35V (vs.Li/Li ^+).

  As described above, in the manufacturing method according to the present embodiment, in the nickel-nickel composite oxide, the nickel content (x) is a high content of 0.75 or more, which contributes to higher energy density. In addition, the metal elements other than nickel occupying nickel sites are cobalt (Co) and aluminum (Al), and they are contained in the ratios (y, z) of the above composition formula, thereby contributing to improvement of cycle characteristics. Yes. In the above composition formula, x, y, and z are preferably 0.75 ≦ x ≦ 0.90, 0.05 ≦ y ≦ 0.20, and 0.02 ≦ z ≦ 0.15, respectively. More preferably, .75 ≦ x ≦ 0.85, 0.10 ≦ y ≦ 0.20, and 0.02 ≦ z ≦ 0.10. In the charge / discharge cycle, the crystal structure can be stabilized by making the c-axis length as close as possible during charge and discharge, and as a result, cycle characteristics can be improved.

  In the lithium ion secondary battery according to the embodiment of the present invention, the electrolytic solution preferably contains at least one selected from fluorinated ether, fluorinated phosphate ester, and cyclic sulfonate ester. These components can improve the oxidation resistance of the electrolytic solution, and can suppress an increase in the amount of gas generated due to an increase in charging voltage and an increase in resistance at the electrode (particularly on the positive electrode side).

  In the embodiment of the present invention, the lithium nickel composite oxide in the positive electrode can be analyzed by an X-ray diffraction method. As this X-ray analysis method, in-situ XRD (X-ray diffraction) measurement focusing on diffraction from the (003) plane of the lithium nickel composite oxide can be performed. In this in-situ XRD measurement, an X-ray diffraction pattern can be obtained by irradiating X-rays in the process of charging a cell by applying a voltage.

FIG. 2 shows an X-ray diffraction pattern (the horizontal axis is the diffraction angle (2θ) and the vertical axis is the diffraction intensity) obtained in Examples described later. In the process of charging the cell with a voltage in the range of 3.0 to 5.2 V vs. Li / Li ⁺ , the H1 phase (003) peak where 2θ before charging (during complete discharge) is around 20.1 ° The strength decreases with increasing voltage. Accordingly, the H2 phase (003) peak appears on the low angle side (within 2θ of 19.5 to 20 °) with respect to the H1 phase (003) peak position, and the intensity gradually increases. When the voltage further increases, the H2 phase (003) peak shifts to the higher angle side as it approaches 4.4V, and overlaps the H1 phase (003) peak position near 4.4V. Further, when the voltage is increased, the H2 phase (003) peak is shifted to a higher angle side than the H1 phase (003) peak. At 5.2 V, the H3 phase (003) peak can be observed as a shoulder on the high angle side.

  Such a change in the H2 phase (003) peak with the charging voltage indicates that the c-axis extends at the beginning of charging and contracts at the end of charging. In the vicinity of 4.4 V, the H2 phase (003) peak position (2θ) coincides with the H1 phase (003) peak position (2θ) in the discharged state. If the voltage in the matched state is the upper limit voltage (end voltage), the c-axis length at full charge and full discharge can be matched, and the crystal structure can be stabilized. Therefore, from the viewpoint of achieving such stabilization of the crystal structure, the difference Δ2θ (the difference between the H2 phase (003) peak position (2θ) at full charge and the H1 phase (003) peak position (2θ) at full discharge is obtained. λ = 1.54Å) is preferably in the range of −0.3 ° to 0.3 °, more preferably in the range of −0.2 ° to 0.2 °, and −0.2 ° to A range of 0.1 ° is particularly preferable.

  Full charge means a state where the battery voltage has reached the upper limit voltage, and complete discharge means a state where the battery voltage has reached the lower limit voltage (end voltage). The upper limit voltage and lower limit voltage are generally determined theoretically depending on the battery material, but in order to suppress battery deterioration, a voltage lower than the theoretical upper limit voltage can be set as the upper limit voltage. A voltage exceeding the voltage can be set as the lower limit voltage.

  The charging rate (SOC) is the ratio (%) of the remaining capacity to the full charge capacity. The full charge capacity is the total amount of electric charge that is discharged when the battery is completely discharged from a full charge at a specified temperature (for example, 25 ° C.) and a constant current. The amount of charge can be obtained by integrating the current (constant). The full charge capacity can be the initial full charge capacity at the first charge.

Lower limit voltage in the lithium ion secondary battery and a manufacturing method thereof is preferably in the range of 2~3.5V (vs.Li/Li ^+), the range of 2~3V (vs.Li/Li ⁺⁾ More preferably, it is in the range of 2.5 to 3 V (vs. Li / Li ⁺ ).

  The lithium ion secondary battery according to the embodiment of the present invention can have the following preferred configuration.

(Positive electrode)
The positive electrode preferably has a structure including a current collector and a positive electrode active material layer formed on the current collector.

  The positive electrode active material layer contains the lithium nickel composite oxide having the layered rock salt structure from the viewpoint of increasing the energy density. The positive electrode active material layer may contain an active material other than this lithium nickel composite oxide, but from the viewpoint of energy density, the content of this lithium nickel composite oxide is preferably 80% by mass or more. More preferably, it is more preferably 95% by mass or more.

BET specific surface area of the positive electrode active material (based on measurements at 77K by a nitrogen adsorption method) is preferably in the range of 0.1 to 1 m ² / g, more preferably 0.3~0.5m ² / g . When the specific surface area of the positive electrode active material is excessively small, the particle size is large, so that cracking is likely to occur during pressing or cycling during electrode production, and there is a tendency for characteristic deterioration to be noticeable. It becomes difficult. On the contrary, when the specific surface area is excessively large, the necessary amount of the conductive auxiliary agent brought into contact with the active material increases, and as a result, it is difficult to increase the energy density. When the specific surface area of the positive electrode active material is in the above range, an excellent positive electrode can be obtained from the viewpoint of energy density and cycle characteristics.

The average particle diameter of the positive electrode active material is preferably 0.1 to 50 μm, more preferably 1 to 30 μm, and further preferably 2 to 25 μm. Here, the average particle diameter means a particle diameter (median diameter: D ₅₀ ) at an integrated value of 50% in a particle size distribution (volume basis) by a laser diffraction scattering method. When the specific surface area of the positive electrode active material is in the above range and the average particle size is in the above range, an excellent positive electrode can be obtained from the viewpoint of energy density and cycle characteristics.

  The positive electrode active material layer can be formed as follows. First, it can be formed by preparing a slurry containing a positive electrode active material, a binder, and a solvent (and optionally a conductive auxiliary agent), applying the slurry onto a positive electrode current collector, drying it, and pressing it as necessary. N-methyl-2-pyrrolidone (NMP) can be used as a slurry solvent used for producing the positive electrode.

  As a binder, what can be normally used as binders for positive electrodes, such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), can be used.

  The content of the binder in the positive electrode active material layer is preferably 1 to 15% by mass, and more preferably 1 to 10% by mass from the viewpoints of binding force and energy density in a trade-off relationship.

  A higher proportion of the positive electrode active material in the positive electrode active material layer is preferable because the capacity per mass increases. However, from the viewpoint of reducing the resistance of the electrode, it is preferable to add a conductive auxiliary agent, from the viewpoint of electrode strength. It is preferable to add a binder. If the proportion of the conductive auxiliary agent is too small, it becomes difficult to maintain sufficient conductivity, and the resistance of the electrode is likely to increase. When the ratio of the binder is too small, it becomes difficult to maintain the adhesive force with the current collector, the active material, and the conductive additive, and electrode peeling may occur.

  Examples of the conductive assistant include carbon black such as acetylene black. Content in the active material layer of a conductive support agent can be set to the range of 1-10 mass%.

  Further, the porosity of the positive electrode active material layer (not including the current collector) constituting the positive electrode is preferably 30% or less, and more preferably 20% or less. When the porosity is high (that is, the electrode density is low), the contact resistance and the charge transfer resistance tend to increase. Therefore, it is preferable to reduce the porosity in this way, and as a result, the electrode density can also be increased. . On the other hand, if the porosity is too low (the electrode density is too high), the contact resistance will be low, but the charge transfer resistance will be high and the rate characteristics will be lowered, so a certain degree of porosity will be secured. It is desirable. From this viewpoint, the porosity is preferably 10% or more, more preferably 12% or more, and may be set to 15% or more.

The porosity means the ratio of the remaining volume, which is obtained by subtracting the volume occupied by particles such as the active material and the conductive auxiliary agent, from the apparent volume of the active material layer as a whole (see the following formula). Therefore, it can be obtained by calculation from the thickness of the active material layer, the mass per unit area, and the true density of particles such as the active material and the conductive additive.
Porosity = (apparent volume of active material layer−volume of particle) / (apparent volume of active material layer)

The “particle volume” (volume occupied by particles contained in the active material layer) in the above formula can be calculated by the following formula.
Particle volume =
(Weight per unit area of active material layer × area of active material layer × content ratio of particles) ÷ true density of particles Here, “area of active material layer” is the side opposite to the current collector side (separator side) ) Plane area.

  The thickness of the positive electrode active material layer is not particularly limited, and can be appropriately set according to desired characteristics. For example, it can be set thick from the viewpoint of energy density, and thin from the viewpoint of output characteristics. Can be set. The thickness of the positive electrode active material layer can be appropriately set within a range of, for example, 10 to 250 μm, preferably 20 to 200 μm, and more preferably 40 to 180 μm.

  As the current collector for the positive electrode, aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used. Examples of the shape include foil, flat plate, and mesh. In particular, an aluminum foil can be suitably used.

  A lithium ion secondary battery according to an embodiment of the present invention includes the positive electrode, a negative electrode, and a nonaqueous electrolyte (for example, an electrolytic solution in which a lithium salt is dissolved). A separator can be provided between the positive electrode and the negative electrode. A plurality of pairs of positive and negative electrodes can be provided.

(Negative electrode)
As the negative electrode active material, materials capable of inserting and extracting lithium, such as lithium metal, carbonaceous material, and Si-based material, can be used. Examples of the carbonaceous material include graphite, amorphous carbon, diamond-like carbon, fullerene, carbon nanotube, and carbon nanohorn. As the Si-based material, Si, SiO ₂ , SiOx (0 <x ≦ 2), a Si-containing composite material, or the like may be used, or a composite containing two or more of these may be used.

  When using lithium metal as the negative electrode active material, melt cooling method, liquid quenching method, atomization method, vacuum deposition method, sputtering method, plasma CVD method, photo CVD method, thermal CVD method, sol-gel method, etc. Thus, a negative electrode can be formed.

  When a carbonaceous material or Si-based material is used as the negative electrode active material, a carbonaceous material (or Si-based material) and a binder such as polyvinylidene fluoride (PVDF) are mixed and dispersed and kneaded in a solvent such as NMP. The negative electrode can be obtained by applying the obtained slurry onto a negative electrode current collector, drying, and pressing as necessary. In addition, after the negative electrode active material layer is formed in advance, a negative electrode can be obtained by forming a thin film to be a current collector by a method such as vapor deposition, CVD, or sputtering. The negative electrode produced in this way has a negative electrode current collector and a negative electrode active material layer formed on the current collector.

The average particle size of the negative electrode active material is preferably 1 μm or more, more preferably 2 μm or more, further preferably 5 μm or more, from the viewpoint of input / output characteristics, from the viewpoint of suppressing side reactions during charge / discharge and suppressing reduction in charge / discharge efficiency. And from the viewpoint of electrode production (smoothness of the electrode surface, etc.), it is preferably 80 μm or less, more preferably 40 μm or less. Here, the average particle diameter means a particle diameter (median diameter: D ₅₀ ) at an integrated value of 50% in a particle size distribution (volume basis) by a laser diffraction scattering method.

  The negative electrode active material layer may contain a conductive aid as necessary. As the conductive auxiliary agent, a conductive material generally used as a negative electrode conductive auxiliary agent such as carbonaceous material such as carbon black, ketjen black, and acetylene black can be used.

  The binder for the negative electrode is not particularly limited, but polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer. Examples include rubber, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamideimide, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, isoprene rubber, butadiene rubber, and fluororubber. . As the slurry solvent, N-methyl-2-pyrrolidone (NMP) or water can be used. When water is used as a solvent, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, and polyvinyl alcohol can be used as a thickener.

  The content of the binder for the negative electrode is preferably in the range of 0.5 to 30% by mass as the content with respect to the negative electrode active material from the viewpoint of the binding force and energy density in a trade-off relationship, The range of ˜25% by mass is more preferable, and the range of 1 to 20% by mass is more preferable.

  As the negative electrode current collector, copper, stainless steel, nickel, titanium, or an alloy thereof can be used.

(Electrolyte)
As the electrolytic solution, a nonaqueous electrolytic solution in which a lithium salt is dissolved in one or two or more nonaqueous solvents can be used.

  Non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate; ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), etc. Chain carbonates; aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate; γ-lactones such as γ-butyrolactone; 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), etc. And cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran. One of these non-aqueous solvents can be used alone, or a mixture of two or more can be used.

Examples of the lithium salt dissolved in the nonaqueous solvent, is not particularly limited, for example _{LiPF 6, LiAsF 6, LiAlCl 4} , LiClO 4, LiBF 4, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (SO ₂ F) ₂ , and lithium bisoxalatoborate are included. These lithium salts can be used individually by 1 type or in combination of 2 or more types. Moreover, a polymer component may be included as a non-aqueous electrolyte. The concentration of the lithium salt can be set in the range of 0.8 to 1.2 mol / L, preferably 0.9 to 1.1 mol / L.

(Oxidation resistance improver)
From the viewpoint of suppressing the generation of gas at a high voltage and the increase in resistance, the electrolytic solution preferably contains an oxidation resistance improver. The oxidation resistance improver preferably contains at least one selected from a fluorinated ether compound, a fluorinated phosphate ester compound, and a cyclic sulfonate ester.

(Fluorinated ether compound)
Examples of the fluorinated ether compound include the following fluorine-containing chain ether compounds.
The fluorine-containing chain ether compound is a compound in which part or all of hydrogen in the chain ether compound is substituted with fluorine. When the fluorine-containing chain ether compound is used, the oxidation resistance of the electrolytic solution is increased, and is particularly suitable for a battery including a positive electrode that operates at a high potential. Fluorine-containing chain ether compounds have higher oxidation resistance as the number of fluorine substitutions increases. However, when the number of fluorine substitutions is too large, reductive decomposition tends to occur, and the electrolyte solution decomposes on the negative electrode side. May become incompatible with the electrolyte solvent. Therefore, the ratio of the number of fluorine atoms to the sum of the number of hydrogen atoms and the number of fluorine atoms in the fluorine-containing chain ether compound is preferably 30% or more and 95% or less, and 40% or more and 90% or less. More preferably, it is 50% or more and 85% or less.

  Although carbon number of a fluorine-containing chain | strand-shaped ether compound is not specifically limited, It is preferable that it is 4-10, and it is more preferable that it is 5-10. The boiling point and melting point of the fluorine-containing chain ether compound vary depending on the number of carbon atoms, but it is preferable that the total number of carbon atoms is 4 or more because the liquid is in the temperature range of actual operation of the secondary battery. Further, it is preferable that the total number of carbon atoms is 10 or less because the viscosity does not become too high and good conductivity of lithium ions can be obtained. The alkyl group bonded to the oxygen atom of the fluorine-containing chain ether compound may be linear or branched, but is preferably linear.

  Examples of the fluorine-containing chain ether compound include 2,2,3,3,3-pentafluoropropyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl 2, 2,2-trifluoroethyl ether, 1H, 1H, 2′H, 3H-decafluorodipropyl ether, 1,1,1,2,3,3-hexafluoropropyl-2,2-difluoroethyl ether, isopropyl 1,1,2,2-tetrafluoroethyl ether, propyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether 1H, 1H, 5H-perfluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1H, 1H, 2′H-perfluorodi Propyl ether, 1H-perfluorobutyl-1H-perfluoroethyl ether, methyl perfluoropentyl ether, methyl perfluorohexyl ether, methyl 1,1,3,3,3-pentafluoro-2- (trifluoromethyl) propyl Ether, 1,1,2,3,3,3-hexafluoropropyl 2,2,2-trifluoroethyl ether, ethyl nonafluorobutyl ether, ethyl 1,1,2,3,3,3-hexafluoropropyl ether 1H, 1H, 5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether, 1H, 1H, 2′H-perfluorodipropyl ether, heptafluoropropyl 1,2,2,2-tetrafluoro Ethyl ether, 1,1,2,2-tetrafluoroethyl-2, , 3,3-tetrafluoropropyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, ethyl nonafluorobutyl ether, methyl nonafluorobutyl ether, bis (2 , 2,3,3-tetrafluoropropyl) ether. These can be appropriately selected from the viewpoints of withstand voltage and boiling point, and may be used alone or in combination of two or more. Among these, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, 1H, 1H, 2'H, 3H-decafluorodipropyl ether, 1H, 1H, 5H- Octafluoropentyl 1,1,2,2-tetrafluoroethyl ether, ethyl 1,1,2,3,3,3-hexafluoropropyl ether, 1H, 1H, 2′H-perfluorodipropyl ether, bis ( 2,2,3,3-tetrafluoropropyl) ether is preferred, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether is more preferred.

Further, from the viewpoint of voltage resistance and compatibility with other electrolytes, the fluorinated ether is preferably a compound represented by the following formula.
^{H- (CY 1 Y 2 -CY 3} Y 4) n -CH 2 O-CY 5 Y 6 -CY 7 Y 8 -H

In the above formula, n is 1, 2, 3 or 4. Y ^{1 to} Y ⁸ are each independently a fluorine atom or a hydrogen atom. However, at least one of Y ^{1 to} Y ⁴ is a fluorine atom, and at least one of Y ^{5 to} Y ⁸ is a fluorine atom. Y ^{1 to} Y ⁴ may be independent for each unit of n.

  The content of the fluorine-containing chain ether compound (the total content when used in combination with the fluorine-containing phosphate compound) is determined based on the solvent (this fluorine-containing chain ether compound and the fluorine-containing phosphate ester compound) constituting the electrolyte solution. In the range of 1 to 95% by volume, more preferably 5% by volume or more, further preferably 10% by volume or more, particularly preferably 20% by volume or more, and 90% by volume or less. More preferably, it is 80 volume% or less, and you may set to 70 volume% or less. By sufficiently containing 1% by volume or more of the fluorine-containing chain ether compound, oxidation resistance can be improved, and low temperature characteristics and electrical conductivity can be improved. In addition, by setting the content of the fluorine-containing chain ether compound to 95% by volume or less in the solvent, compatibility with other solvent components can be improved, and battery characteristics can be stably obtained.

(Fluorinated phosphate compound)
The fluorine-containing phosphate compound used in the present invention is preferably a compound represented by the following formula (3).

In formula (3), R ³¹ , R ³² and R ³³ each independently represents an alkyl group having 1 to 5 carbon atoms or a fluorine-substituted alkyl group having 1 to 5 carbon atoms, and at least one of these is fluorine-substituted. It is an alkyl group.

  By containing the fluorine-containing phosphate ester compound in the electrolytic solution, the oxidation resistance of the electrolytic solution can be enhanced, and the compatibility with other solvent components and the ionic conductivity of the electrolytic solution can be enhanced. . In particular, when a fluorine-containing phosphate compound is used as an electrolyte solution solvent for a battery including a positive electrode that operates at a high potential, decomposition of the electrolyte solution at a high potential is suppressed, which is preferable. The fluorine-containing phosphate ester compound has higher oxidation resistance as the number of fluorine substitutions increases. However, when the number of fluorine substitutions is too large, reductive decomposition tends to occur, and the electrolyte solution decomposes on the negative electrode side. May become incompatible with the electrolyte solvent. Accordingly, the ratio of the number of fluorine atoms to the sum of the number of hydrogen atoms and the number of fluorine atoms in the fluorine-containing phosphate compound is preferably 30% or more and 100% or less, and 35% or more and 95% or less. More preferably, it is 40% or more and 90% or less. Of the compounds represented by the formula (3), a fluorine-containing phosphate compound represented by the following formula (3-1) is particularly preferable.

O = P (OCH ₂ Ra) ₃ (3-1)
[In the formula (3-1), each Ra independently represents a fluorine-substituted alkyl group having 1 to 4 carbon atoms. ]

  In formula (3-1), the three Ras are preferably the same fluorine-substituted alkyl group, and Ra preferably has 1 to 3 carbon atoms. Further, Ra preferably has at least one fluorine atom bonded to each carbon atom.

  Examples of the fluorine-containing phosphate compound used in the present invention include 2,2,2-trifluoroethyl dimethyl phosphate, bis (trifluoroethyl) methyl phosphate, bis (trifluoroethyl) ethyl phosphate, and phosphoric acid. Tris (trifluoromethyl), pentafluoropropyldimethyl phosphate, heptafluorobutyldimethyl phosphate, trifluoroethyl methyl ethyl phosphate, pentafluoropropyl methyl ethyl phosphate, heptafluorobutyl methyl ethyl phosphate, trifluoroethyl phosphate Methylpropyl, pentafluoropropylmethylpropyl phosphate, heptafluorobutylmethylpropyl phosphate, trifluoroethylmethylbutyl phosphate, pentafluoropropylmethylbutyl phosphate, heptafluorobutylmethylbutyl phosphate, Trifluoroethyl diethyl acid, pentafluoropropyl diethyl phosphate, heptafluorobutyl diethyl phosphate, trifluoroethyl ethyl propyl phosphate, pentafluoropropyl ethyl propyl phosphate, heptafluorobutyl ethyl propyl phosphate, trifluoroethyl ethyl phosphate Butyl, pentafluoropropylethyl butyl phosphate, heptafluorobutyl ethyl butyl phosphate, trifluoroethyl dipropyl phosphate, pentafluoropropyl dipropyl phosphate, heptafluorobutyl dipropyl phosphate, trifluoroethyl propyl butyl phosphate, Pentafluoropropylpropyl butyl phosphate, heptafluorobutyl propyl butyl phosphate, trifluoroethyl dibutyl phosphate, pentafluoropropyl dibutyl phosphate, Heptafluorobutyldibutyl acid, Tris phosphate (2,2,3,3-tetrafluoropropyl), Tris phosphate (2,2,3,3,3-pentafluoropropyl), Tris phosphate (2,2, 2-trifluoroethyl), tris phosphate (1H, 1H-heptafluorobutyl), and tris phosphate (1H, 1H, 5H-octafluoropentyl). Of these, tris phosphate (2,2,2-trifluoroethyl) and tris phosphate (1H, 1H-heptafluorobutyl) are preferable, and tris phosphate (2,2,2-trifluoroethyl) is particularly preferable. preferable.

  These fluorine-containing phosphate ester compounds can be used alone or in combination of two or more.

  The content of the fluorine-containing phosphate ester compound (the total content when used in combination with the above-mentioned fluorine-containing chain ether) is the solvent constituting the electrolyte (this fluorine-containing phosphate ester compound and the fluorine-containing chain ether are solvents) 1) to 95% by volume, preferably 5% by volume or more, more preferably 10% by volume or more, particularly preferably 20% by volume or more, and more preferably 90% by volume or less. Preferably, 80 volume% or less is more preferable, and you may set to 70 volume% or less. By sufficiently containing 1% by volume or more of the fluorine-containing phosphate compound, the oxidation resistance can be improved, and the low-temperature characteristics and conductivity can also be improved. Further, by setting the content of the fluorine-containing phosphate ester compound to 95% by volume or less in the solvent, the compatibility with other solvent components can be improved and the battery characteristics can be stably obtained.

(Cyclic sulfonic acid compound)
As the cyclic sulfonic acid compound, a compound represented by the following formula (5) or (6) can be used.

In formula (5), R ₁₀₁ and R ₁₀₂ each independently represent a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 4 carbon atoms. n is 1, 2, 3, or 4.

In Formula (6), R ₂₀₁ , R ₂₀₂ , R ₂₀₃ and R ₂₀₄ each independently represent a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 4 carbon atoms. n is 1, 2, 3, or 4.

  Examples of the cyclic sulfonate ester include 1,3-propane sultone, 1,2-propane sultone, 1,4-butane sultone, 1,2-butane sultone, 1,3-butane sultone, 2,4-butane sultone, 1,3 -Monosulfonic acid ester such as pentane sultone; ethylene methane disulfonic acid ester (EMDS) represented by the following formula, α-methylethylene methane disulfonic acid ester (αMe-EMDS) represented by the following formula, methylene methane disulfone represented by the following formula Examples thereof include acid esters (MMDS) and disulfonic acid esters such as α-methylmethylenemethane disulfonic acid ester (3MDT) represented by the following formula.

  Moreover, as other cyclic disulfonic acid ester, the compound (BDT) represented by a following formula is also mentioned.

  Among these, 1,3-propane sultone, 1,4-butane sultone, methylene methane disulfonate (MMDS), ethylene methane disulfonate (EMDS), α-methyl ethylene methane disulfonate (αMe-EMDS), α-methyl Methylene methane disulfonate (3MDT) and BDT are preferred, 1,3-propane sultone, 1,4-butane sultone, methylene methane disulfonate (MMDS), ethylene methane disulfonate (EMDS), α-methyl ethylene methane disulfonate Esters (αMe-EMDS) and α-methylmethylenemethane disulfonate (3MDT) are more preferable, and MMDS and 1,3-propane sultone are particularly preferable.

  The content of the cyclic sulfonic acid ester in the electrolytic solution is preferably 0.01 to 10% by mass, and more preferably 0.1 to 5% by mass. When the content of the cyclic sulfonic acid ester is 0.01% by mass or more, a coating can be more effectively formed on the positive electrode surface to suppress decomposition of the electrolytic solution. When the content of the cyclic sulfonic acid ester is 10% by mass or less, the viscosity and conductivity of the electrolytic solution can be adjusted within a more appropriate range, and sufficient initial capacity can be secured by charging at 20 ° C.

  It is preferable that the electrolyte solution in this embodiment contains a carbonate compound as a non-aqueous solvent, and the above-mentioned cyclic carbonate compound and chain carbonate compound can be used as the carbonate compound. The carbonate compound preferably contains at least a cyclic carbonate compound. By using a cyclic carbonate compound, the ion dissociation of the electrolytic solution is improved and the viscosity of the electrolytic solution is lowered. Therefore, ion mobility can be improved. The content of the cyclic carbonate compound in the total solvent is preferably 5% by volume or more, more preferably 10% by volume or more, preferably 70% by volume or less, more preferably 50% by volume or less, and further preferably 40% by volume or less. .

  When chain carbonate is included as the carbonate compound, the content of the chain carbonate compound is not particularly limited, but from the viewpoint of lowering the viscosity of the electrolyte solution, 1 to 90% by volume in the solvent constituting the electrolyte solution In view of obtaining a sufficient addition effect, it is preferably 3% by volume or more, more preferably 70% by volume or less from the viewpoint of obtaining a sufficient blending effect with another solvent, and 50% by volume or less. More preferred is 30% by volume or less.

The electrolytic solution in the present embodiment preferably contains at least one selected from a fluorinated ether, a fluorinated phosphate ester, and a cyclic sulfonate ester, and a cyclic carbonate compound. At least one of the fluorinated ether and the fluorinated phosphate ester is preferable. More preferably, it contains a cyclic sulfonate ester and a cyclic carbonate compound. Since the cyclic carbonate compound has a large relative dielectric constant, the ion dissociation property of the electrolytic solution is improved. Further, since the viscosity of the electrolytic solution is lowered, the ion mobility is improved. However, when a cyclic carbonate compound is used as the electrolytic solution, the cyclic carbonate compound tends to be decomposed and a gas composed of CO ₂ tends to be generated. In particular, in the case of a secondary battery including a positive electrode active material that operates at a potential of 4.5 V or more, gas tends to be generated. Therefore, in this embodiment, a battery using a positive electrode active material that operates at a relatively high potential by using an electrolytic solution containing at least one selected from fluorinated ethers, fluorinated phosphate esters, and cyclic sulfonate esters. Even so, the effect of improving the cycle characteristics can be obtained. This is presumed to be an effect obtained not only by the fluorinated ether or fluorinated phosphate ester acting as a solvent but also by assisting the formation of a film of the cyclic sulfonate ester.

(Separator)
As the separator, a porous resin film, a woven fabric, a non-woven fabric, or the like can be used. Examples of the resin constituting the porous film include polyolefin resins such as polypropylene and polyethylene, polyester resins, acrylic resins, styrene resins, and nylon resins. In particular, a polyolefin-based microporous membrane is preferable because of its excellent ion permeability and performance of physically separating the positive electrode and the negative electrode. If necessary, the separator may be formed with a layer containing inorganic particles. Examples of the inorganic particles include insulating oxides, nitrides, sulfides, carbides, etc. Among them, TiO. ₂ or Al ₂ O ₃ is preferably included.

(Exterior body)
A case made of a flexible film, a can case, or the like can be used for the exterior body (exterior container), and a flexible film is preferably used from the viewpoint of reducing the weight of the battery.

  As the flexible film, a film in which a resin layer is provided on the front and back surfaces of a metal layer serving as a base material can be used. As the metal layer, a metal layer having a barrier property such as prevention of leakage of the electrolytic solution or entry of moisture from the outside can be selected, and aluminum, stainless steel, or the like can be used. On at least one surface of the metal layer, a heat-fusible resin layer such as a modified polyolefin is provided. An exterior container is formed by making the heat-fusible resin layers of the flexible film face each other and heat-sealing the periphery of the portion that houses the electrode laminate. A resin layer such as a nylon film or a polyester film can be provided on the surface opposite to the surface on which the heat-fusible resin layer is formed.

(Production of electrodes)
In the production of the electrode, as an apparatus for forming the active material layer on the current collector, a doctor blade, an apparatus for performing various coating methods such as a die coater, a gravure coater, a transfer method, an evaporation method, and the like. A combination of applicators can be used. In order to form the coated end portion of the active material with high accuracy, it is particularly preferable to use a die coater. The active material application method using a die coater is roughly divided into a continuous application method in which an active material is continuously formed along the longitudinal direction of a long current collector, and an active material application method along the longitudinal direction of the current collector. There are two types of intermittent application methods in which the application part and the non-application part are alternately and repeatedly formed, and these methods can be selected as appropriate.

(Configuration example of lithium ion secondary battery)
FIG. 1 shows a cross-sectional view of an example (laminated type) lithium ion secondary battery according to an embodiment of the present invention. As shown in FIG. 1, the lithium ion secondary battery of this example includes a positive electrode current collector 3 made of a metal such as an aluminum foil and a positive electrode active material layer 1 containing a positive electrode active material provided thereon. And a negative electrode current collector 4 made of a metal such as copper foil and a negative electrode active material layer 2 containing a negative electrode active material provided thereon. The positive electrode and the negative electrode are laminated via a separator 5 made of a nonwoven fabric or a polypropylene microporous film so that the positive electrode active material layer 1 and the negative electrode active material layer 2 face each other. This electrode pair is accommodated in a container formed of exterior films 6 and 7 made of an aluminum laminate film. A positive electrode tab 9 is connected to the positive electrode current collector 3, a negative electrode tab 8 is connected to the negative electrode current collector 4, and these tabs are drawn out of the container. An electrolytic solution is injected into the container and sealed. It can also be set as the structure where the electrode group by which the several electrode pair was laminated | stacked was accommodated in the container.

  The following examples further illustrate the present invention.

(In-situ XRD measurement of positive electrode active material)
In-situ XRD measurement was performed as follows for the lithium nickel composite oxide having a layered rock salt structure used in this example, comparative reference example, and comparative example. Table 1 shows Δ2θ obtained from the measurement results.

Lithium nickel composite oxide (composition formula: LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _0.87 Co _0.1 Al _0.03 O ₂ , or LiNi _0.8 Co _0.1 Mn _{0 0.1} O ₂ ), a conductive aid, a binder, and a solvent (NMP) were mixed to form a slurry, which was applied onto an Al foil and dried to obtain a positive electrode. The positive electrode and the counter electrode (metallic lithium) were laminated via a separator, and a beryllium plate was further arranged on the positive electrode current collector side to produce a cell with a beryllium window. As the electrolytic solution, a solution of 1 mol / L lithium hexafluorophosphate (LiPF ₆ ) dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC: DEC = 3: 7) is used. It was.

In the process of charging the cell by applying a voltage in the range of 3.0 to 5.2 V (vs. Li / Li ⁺ ), XRD measurement was performed by irradiating X-rays from the beryllium plate side.

FIG. 2 shows in-situ XRD measurement results focusing on diffraction from the (003) plane of a lithium nickel composite oxide (composition formula: LiNi _0.8 Co _0.15 Al _0.05 O ₂ ). This figure shows the results in the range of 3.0 to 5.2 V (vs. Li / Li ⁺ ). The vertical axis represents intensity (arb. Unit), and the horizontal axis represents 2θ (λ = 1.54Å).

As shown in this figure, it can be seen that the reaction (desorption of lithium ions) proceeds through three types of phases (H1, H2, and H3) in the charging process. The peak of the first phase (H1) is observed from the initial charge (near 3.0 V (vs. Li / Li ⁺ )) to near 4.1 V (vs. Li / Li ⁺ ), and the peak position changes during that time. The peak intensity gradually decreases. In addition, the second phase (H2) peak occurs on the low angle side until it reaches 3.9 V (vs. Li / Li ⁺ ) for a while after the start of charging, and then the intensity gradually increases. It moves from the vicinity of 4.2 V (vs. Li / Li ⁺ ) to the high angle side, and overlaps with the peak position of the first phase (H1) in the vicinity of 4.4 V (vs. Li / Li ⁺ ). Thereafter, the peak of the second phase (H2) moves to the higher angle side than the peak position of the first phase (H1). Furthermore, around 5 V (vs. Li / Li ⁺ ), the third phase (H3) occurs on the high angle side. When the voltage exceeds 4.4 V (vs. Li / Li ⁺ ), that is, when the peak of the second phase (H2) greatly exceeds the peak position of the first phase (H1), the phase change (structural change) increases. It is thought that it becomes a cause of a cycle characteristic fall.

  The secondary battery according to the present invention has a difference Δ2θ (λ = 1) between the H2 phase (003) peak position (2θ) at full charge and the H1 phase (003) peak position (2θ) at full discharge by the X-ray diffraction method. .54Å) is in the range of −0.3 ° to 0.3 °, the state before the phase change becomes large as described above is maintained, and good cycle characteristics can be obtained.

(Production of battery and evaluation of cycle characteristics)
Using lithium nickel composite oxide having a layered rock salt structure as a positive electrode active material, a lithium ion secondary battery was fabricated as follows, and the cycle characteristics were evaluated.

Example 1
Lithium nickel composite oxide having a layered rock salt structure in the positive electrode active material (composition formula: LiNi _0.8 Co _0.15 Al _0.05 O ₂ ) (BET specific surface area: 0.46 m ² / g), conductive auxiliary agent A slurry in which carbon black is used as a binder and polyvinylidene fluoride (PVDF) is used as a binder, and these are mixed and dispersed in an organic solvent so that the mass ratio is positive electrode active material: conductive aid: binder = 93: 4: 3. Was prepared. This was applied to a positive electrode current collector (aluminum foil) and dried to form a positive electrode active material layer on both sides. This was rolled with a roller press and processed into a predetermined size to obtain a positive electrode sheet.

  Using a graphite whose surface was coated with amorphous carbon as a negative electrode active material, PVDF was used as a binder, and these were mixed to prepare a slurry dispersed in an organic solvent. This was applied to a negative electrode current collector (copper foil) and dried to form negative electrode active material layers on both sides. This was rolled with a roller press and processed into a predetermined size to obtain a negative electrode sheet.

One positive electrode sheet and two negative electrode sheets thus prepared were alternately laminated via a separator made of polypropylene having a thickness of 25 μm. A negative electrode terminal and a positive electrode terminal were attached thereto, accommodated in an outer container made of an aluminum laminate film, and an electrolyte solution in which a lithium salt was dissolved was added and sealed to obtain a laminated lithium ion secondary battery. Note that a mixed solution of EC and DEC (EC / DEC = 3/7 (volume ratio)) was used as a solvent for the electrolytic solution, and 1 mol / L of LiPF ₆ as a lithium salt was dissolved in this mixed solvent.

  About the obtained battery, the charge / discharge test was done as follows and the capacity | capacitance maintenance factor was calculated | required. The results are shown in FIG.

(Charge / discharge cycle test)
At 45 ° C., charge / discharge cycle test (Cycle-Rate: 1C, CC-CV charge, constant voltage charge time: 2.5 hours, charge voltage (upper limit voltage): listed in Table 1, CC discharge, lower limit voltage: 2. 5V) and tested up to 300 cycles. The ratio of the discharge capacity after 300 cycles to the initial discharge capacity was defined as the capacity retention rate (%). The results are shown in Table 1.

(Examples 2 to 4)
A secondary battery was produced in the same manner as in Example 1 except that the charge upper limit voltage was as shown in Table 1, and a charge / discharge cycle test was performed. The results are shown in Table 1 together with the results of Example 1.

(Example 5)
The positive electrode active material is converted into a lithium nickel composite oxide ((composition formula: LiNi _0.87 Co _0.1 Al _0.03 O ₂ ) (BET specific surface area: 0.46 m ² / g)) having a high nickel content. Instead, a battery was produced in the same manner as in Example 1 except that the charge upper limit voltage was as shown in Table 1, and a charge / discharge cycle test was performed. The results are shown in Table 1.

(Comparative Examples 1 and 2)
Implementation was carried out except that the positive electrode active material was replaced with lithium nickel composite oxide containing Mn (NCM: LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ) and the charge upper limit voltage was as shown in Table 1. A secondary battery was produced in the same manner as in Example 1, and a charge / discharge cycle test was performed. The results are shown in Table 1.

(Comparative Reference Examples 1 and 2)
A secondary battery was produced in the same manner as in Example 1 except that the charge upper limit voltage was as shown in Table 1, and a charge / discharge cycle test was performed. The results are shown in Table 1 together with the results of Example 1.

(Comparative Reference Examples 3 and 4)
A secondary battery was produced in the same manner as in Example 5 except that the charge upper limit voltage was as shown in Table 1, and a charge / discharge cycle test was performed. The results are shown in Table 1 together with the results of Example 1.

  As shown in Table 1, it can be seen that the secondary batteries of Examples 1 to 4 are superior in capacity and cycle characteristics to the secondary batteries of Comparative Reference Examples 1 and 2. Similarly, it can be seen that the secondary battery of Example 5 is superior in capacity and cycle characteristics to the secondary batteries of Comparative Reference Examples 3 and 4. In addition, the absolute value of Δ2θ in Examples 1 to 4 is smaller than the absolute value of Δ2θ in Comparative Reference Examples 1 and 2, and the absolute value of Δ2θ in Example 5 is smaller than the absolute value of Δ2θ in Comparative Reference Examples 3 and 4. I understand that it is small.

  In addition, as shown in Table 1, the secondary battery of Comparative Example 2 having a charging upper limit voltage of 4.3V is larger in capacity than the secondary battery of Comparative Example 1 having a charging upper limit voltage of 4.1V. It can be seen that the cycle characteristics are inferior. Moreover, it turns out that the secondary battery of the comparative example 2 whose charge upper limit voltage is 4.3V is inferior in capacity maintenance rate compared with Example 2 and 5 whose charge upper limit voltage is the same 4.3V. Thus, it can be seen that in the case of a normal secondary battery, the cycle characteristics are low when the charging voltage is increased to around 4.3V. In the n-situ XRD measurement of the positive electrode active material used in Comparative Example 2, the H2 phase (003) peak disappeared and the H3 phase (003) peak was observed at 4.3 V.

DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 2 Negative electrode active material layer 3 Positive electrode collector 4 Negative electrode collector 5 Separator 6 Laminate exterior film 7 Laminate exterior film 8 Negative electrode tab 9 Positive electrode tab

Claims (6)

A positive electrode including a lithium nickel composite oxide having a layered rock salt structure as a positive electrode active material; a negative electrode including a negative electrode active material capable of occluding and releasing lithium ions; an electrolyte; and an outer package,
The lithium nickel composite oxide has a composition formula LiNi _x Co _y Al _z O ₂ (0.75 ≦ x ≦ 0.95, 0.03 ≦ y ≦ 0.20, 0.02 ≦ z ≦ 0.15, x + y + z = 1)
The difference Δ2θ (λ = 1.54Å) between the H2 phase (003) peak position (2θ) at the time of full charge and the H1 phase (003) peak position (2θ) at the time of complete discharge is −0.3 by the X-ray diffraction method. A lithium ion secondary battery characterized by being in the range of ° to 0.3 °. 2. The lithium ion secondary battery according to claim 1, wherein a charge upper limit voltage is in a range of 4.25 to 4.45 V (vs. Li / Li ⁺ ).   3. The lithium ion secondary battery according to claim 1, wherein the electrolytic solution contains at least one selected from a fluorinated ether, a fluorinated phosphate ester, and a cyclic sulfonate ester. Method for producing a lithium ion secondary battery including a positive electrode including a lithium nickel composite oxide having a layered rock salt structure as a positive electrode active material, a negative electrode including a negative electrode active material capable of occluding and releasing lithium ions, an electrolyte, and an outer package Because
Forming a positive electrode;
Forming a negative electrode;
Containing the positive electrode, the negative electrode, and the electrolytic solution in the outer package;
The lithium nickel composite oxide has a composition formula LiNi _x Co _y Al _z O ₂ (0.75 ≦ x ≦ 0.95, 0.03 ≦ y ≦ 0.20, 0.02 ≦ z ≦ 0.15, x + y + z = 1)
The difference Δ2θ (λ = 1...) Between the H2 phase (003) peak position (2θ) when the lithium nickel composite oxide is fully charged and the H1 phase (003) peak position (2θ) when fully discharged by the X-ray diffraction method. 54Å) is set such that the charging upper limit voltage is in the range of −0.3 ° to 0.3 °, and the method for producing a lithium ion secondary battery. The manufacturing method of the lithium ion secondary battery of Claim 4 which sets the said charge upper limit voltage to the range of 4.25-4.45V (vs.Li/Li ^<+> ).   The method for producing a lithium ion secondary battery according to claim 4 or 5, wherein the electrolytic solution contains at least one selected from a fluorinated ether, a fluorinated phosphate ester, and a cyclic sulfonate ester.

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