JP2003331922A - Cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cell in which capacity can be increased. <P>SOLUTION: The potential of a positive electrode 12, against lithium metal when charging, is controlled so as to become 3.7 V or higher and 4.0 V or lower, and the potential of a negative electrode 14, against lithium metal when charging, is controlled so as to become 0.4 V or lower and 0.1 V or higher. The capacity is increased by reducing an utilization rate of the negative electrode 14 and by increasing an utilization rate of the positive electrode 12. The positive electrode 12 contains scaly graphite and amorphous carbon as conducting agent. It is recommendable to make the positive electrode 12 contain the scaly graphite by 3 to 7 mass%, and to make the mass ratio of scaly graphite to amorphous carbon 6:4 to 7:2. The capacity is increased by heightening the conductivity of the positive electrode 12. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a battery provided with an electrolyte in addition to a positive electrode and a negative electrode.

[0002]

2. Description of the Related Art Recently, a camera-integrated VTR (videotape)
Many portable electronic devices such as recorders), mobile phones, and laptop computers have appeared, and their size and weight have been reduced. Along with this, research and development for improving the energy density of batteries, especially secondary batteries, have been actively promoted as portable power supplies for these electronic devices. Among them, the lithium ion secondary battery is highly expected because it can obtain a larger energy density than a lead battery or a nickel cadmium battery, which are conventional non-aqueous electrolyte secondary batteries.

[0003]

However, the recent advances in the performance and multifunction of portable electronic equipment are remarkable, and accordingly, the lithium ion secondary battery is required to have a larger capacity. .

FIG. 5 shows the charging characteristics of a general lithium ion secondary battery. Thus, the battery voltage is represented by the difference between the positive electrode potential and the negative electrode potential. Therefore, when the operating voltage of the battery is set to 3.6 V, for example, the design voltage of the positive electrode is set to 3.6 V and the design voltage of the negative electrode is set to 0 V, or the design voltage of the positive electrode is set to 4.0 V and the design voltage of the negative electrode is set. The voltage is set to 0V and the battery is charged to 3.6V before use.

However, the capacity of the battery cannot be increased by such a method. This is because FIG. 6 shows the capacity of LiNiO ₂ when lithium metal is used for the counter electrode, but as shown in FIG. 6, when the charging voltage is lowered, the charging capacity decreases and the charging / discharging efficiency also increases. Because it will decrease.

Further, the lithium ion secondary battery uses a non-aqueous electrolyte having a lower ionic conductivity than an aqueous solution, but by shortening the distance between the electrodes and increasing the working area of the electrode, it becomes an aqueous battery. It enables charging and discharging with a comparable large current. However, in the case of a so-called coin-type battery in which a disk-shaped positive electrode and a negative electrode are arranged so as to face each other with an electrolyte in between, a working area of the electrode cannot be increased, and therefore a sufficient capacity at a large current cannot be obtained.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a battery whose capacity can be increased.

[0008]

A first battery according to the present invention comprises a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte, and the positive electrode is a positive electrode active material. As the potential of at least one of lithium-nickel composite oxide and lithium-manganese composite oxide, the potential with respect to lithium metal during charging of the positive electrode is 3.7 V or higher and does not become higher than 4.0 V. The potential of the negative electrode with respect to lithium metal during charging is 0.4 V or less and does not become smaller than 0.1 V.

In a second battery according to the present invention, a disk-shaped positive electrode and a negative electrode are arranged so as to face each other via an electrolyte, and the positive electrode contains lithium and at least one transition metal as a positive electrode active material. In addition to containing a complex oxide containing
It contains scaly graphite and amorphous carbon as a conductive agent, and the content of scaly graphite in the positive electrode is 3% by mass or more and 7% by mass or less, and the mass ratio of scaly graphite to amorphous carbon is scaly. Graphite: amorphous carbon = 6: 4 to 7: 2.

In the first battery according to the present invention, the potential with respect to the lithium metal when the positive electrode is charged is 3.7 V or more and does not exceed 4.0 V, and the potential with respect to the lithium metal when the negative electrode is charged is 0. Since the voltage is set to 4 V or less and not lower than 0.1 V, the utilization factor of the negative electrode is reduced, the utilization factor of the positive electrode is increased, and the battery capacity is increased.

In the second battery according to the present invention, the positive electrode contains scaly graphite and amorphous carbon as a conductive agent, and the content of the scaly graphite in the positive electrode is 3% by mass or more and 7% by mass or less, Since the mass ratio of the scaly graphite and the amorphous carbon was set to be scaly graphite: amorphous carbon = 6: 4 to 7: 2, the conductivity of the positive electrode is improved and the battery capacity is improved.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]

FIG. 1 shows a sectional structure of a secondary battery according to a first embodiment of the present invention. This secondary battery is of a so-called coin type, in which a disk-shaped positive electrode 12 housed in a positive electrode can 11 and a disk-shaped negative electrode 14 housed in a negative electrode can 13 are separated by a separator 15. Are stacked. The interiors of the positive electrode can 11 and the negative electrode can 13 are filled with an electrolytic solution 16 which is a liquid electrolyte, and the peripheral portions of the positive electrode can 11 and the negative electrode can 13 are sealed by being caulked with an insulating gasket 17.

The positive electrode can 11 and the negative electrode can 13 are, for example,
Each is made of metal such as stainless steel or aluminum. The positive electrode can 11 functions as a current collector for the positive electrode 12, and the negative electrode can 13 functions as a current collector for the negative electrode 14.

The positive electrode 12 contains, for example, a positive electrode active material,
It is composed of a conductive agent and a binder as required. At least one of lithium-nickel composite oxide and lithium-manganese composite oxide is used as the positive electrode active material.
Seed. The lithium-nickel composite oxide is a composite oxide containing lithium and nickel, for example, L
iNiO ₂ is used. Further, the lithium-manganese composite oxide is a composite oxide containing lithium and manganese represented by the general formula _{Li x Mn 2-y MI y} O 4 is used. MI is a transition metal except manganese (Mn), magnesium (Mg) and aluminum (A
l) represents at least one of the group consisting of x and y vary depending on the charging / discharging state of the battery, and are usually values within the ranges of 0.05 ≦ x ≦ 1.10 and 0 ≦ y <1.

Further, in addition to such a lithium-nickel composite oxide or a lithium-manganese composite oxide, another lithium composite oxide represented by the general formula Li _z MIIO ₂ may be used. MII represents at least one kind of transition metal. z varies depending on the charging / discharging state of the battery, and is usually a value within the range of 0.05 ≦ z ≦ 1.10.

As the conductive agent, for example, graphite, carbon black, acetylene black or carbon fiber is used. Further, as the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, hexafluoropropylene, a copolymer of polyvinylidene fluoride and hexafluoropropylene, styrene-butadiene rubber, etc. are used.

The negative electrode 14 is, for example, a negative electrode active material.
A negative electrode material capable of occluding and releasing titanium.
It contains any one or more of the
Composed with a binder such as polyvinylidene fluoride depending on
Has been. As a negative electrode material capable of inserting and extracting lithium
Are, for example, carbonaceous materials, metal compounds, silicon, silicon
Compounds or conductive polymers can be mentioned, any of these
These are used alone or in combination of two or more. Carbonaceous
Materials include artificial graphite, natural graphite, and non-graphitizable carbon.
Rui or easily graphitizable carbon can be used as a metal compound.
Is SnSiO ₃Or SnO₂Oxides such as
The conductive polymer used is polyacetylene or polyethylene.
Examples include lipyrole. Among them, carbonaceous materials are
Very little change in crystal structure that occurs during charge and discharge and high
Charge and discharge capacity can be obtained and good cycle
It is preferable because the characteristics can be obtained.

The separator 15 separates the positive electrode 12 and the negative electrode 14 from each other and prevents current short circuit due to contact between both electrodes.
It passes lithium ions. The separator 15 is made of, for example, a synthetic resin porous film made of polytetrafluoroethylene, polypropylene, polyethylene or the like, or a porous film made of an inorganic material such as a ceramic non-woven fabric.
It may have a structure in which at least one kind of porous film is laminated.

The electrolytic solution 16 is a lithium salt as an electrolyte salt in a solvent.
It is a solution of um salt and the lithium salt is ionized.
As a result, it exhibits ionic conductivity. Richi
Examples of the um salt include LiBF_Four, LiPF₆, L
iAsF₆, LiSbF₆, LiCF₃SO₃, LiC
H₃SO₃, LiClO_Four, LiN (C_nF_{2n + 1}S
O ₂)₂(N is an integer of 1 or more) and the like.
Any one of them or a mixture of two or more of them
Can be

Examples of the solvent include cyclic carbon ester compounds, chain carbonic acid ester compounds, ester compounds,
Alternatively, a nonaqueous solvent such as an ether compound may be used, and any one of these may be used alone, or two or more of them may be mixed and used. Examples of the cyclic carbon ester compound include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and the like, and a cyclic carbonate compound in which hydrogen is replaced by a halogen or a halogenated acryl group. Examples of the chain carbonate compound include dimethyl carbonate and ethyl carbonate. Methyl, diethyl carbonate, propyl methyl carbonate, ethyl propyl carbonate,
There are dipropyl carbonate and those in which hydrogen of these compounds is replaced with halogen, ester compounds include methyl acetate, methyl formate and methyl propionate, and ether compounds include dimethoxymethane, tetrahydrofuran and 1,3-dioxane. Etc.

Instead of the electrolytic solution 16, a gel electrolyte prepared by mixing, dissolving, and absorbing an electrolytic solution in which a lithium salt is dissolved at a concentration of 0.5 to 2.0 mol / l with a polymer compound is used. Also, the lithium salt is a polyolefin,
A solid electrolyte dissolved in a polymer compound such as polyesters, polyethers, polyamides, polyurethanes, alkyd resin compounds and organic polysilicons may be used.

Further, in this secondary battery, the potential of lithium metal when the positive electrode 12 is charged is 3.7 V or more and does not exceed 4.0 V, and the potential of lithium metal when the negative electrode 14 is charged is 0. The voltage is set to 0.4 V or less and not lower than 0.1 V. That is, normally, lithium is occluded until the potential of the negative electrode 14 becomes 0, but in this secondary battery, the utilization of the negative electrode 14 is reduced by stopping the absorption of lithium in the negative electrode 14 midway. The electric potential is set higher than usual. As a result, in the present embodiment, the potential of the positive electrode 12 is increased, the utilization factor is increased, and the capacity is increased. Furthermore, the potential of the positive electrode 12 with respect to the lithium metal during charging becomes 3.75 V or higher and does not become higher than 3.95 V, so that the negative electrode 14
The potential for lithium metal during charging is 0.35
The voltage is preferably set to V or less and not lower than 0.15V. The utilization rate of the negative electrode 14 is the capacity of the negative electrode 14 at the end of charging,
It refers to the ratio to the capacity when charged until the potential of 4 becomes 0.

As described above, in order to reduce the utilization rate of the negative electrode 14, it is preferable to use a material having a high average voltage during charging as the negative electrode active material. The mass ratio of the negative electrode active material to the positive electrode active material (negative electrode active material mass / positive electrode active material mass) is preferably 20/53 or more and 32/29 or less.
By adjusting in this manner, the positive electrode 12 and the negative electrode 14
This is because the potential of can be controlled as described above.

This secondary battery can be manufactured, for example, as follows.

First, for example, the positive electrode active material, the conductive agent, and the binder described above are mixed to prepare a positive electrode mixture, and then the positive electrode mixture is compression molded into a pellet shape to form the positive electrode 12. Create. Further, in addition to the positive electrode active material, the conductive agent and the binder, a solvent such as N-methyl-2-pyrrolidone is added and mixed to prepare a positive electrode mixture,
The positive electrode mixture may be dried and then compression molded. At that time, the positive electrode active material may be used as it is or may be dried and used, but it is preferable to sufficiently dry it because it reacts with water and the function as the positive electrode active material is impaired.

Next, a negative electrode material capable of occluding and releasing lithium as a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the obtained negative electrode mixture is compression molded into a pellet shape. Thus, the negative electrode 14 is manufactured. In addition, a negative electrode mixture is prepared by adding and mixing a solvent such as N-methyl-2-pyrrolidone in addition to a negative electrode material capable of inserting and extracting lithium and a binder, and drying the negative electrode mixture. You may make it compression-mold after making it.

After that, for example, the positive electrode 12, the separator 15 and the negative electrode 14 are laminated in this order and placed in the positive electrode can 11, and the electrolytic solution 16 is injected, and then the positive electrode can 11 and the negative electrode can 13 are inserted via the gasket 17. Crimp. This allows
The secondary battery shown in FIG. 1 is formed.

This secondary battery operates as follows.

In this secondary battery, when charged, for example, lithium ions are released from the positive electrode 12 and the electrolyte 16
It is occluded in the negative electrode 14 via When discharged, for example, lithium ions are released from the negative electrode 14 and the electrolyte 16
It is occluded in the positive electrode 12 via At that time, the potential of the positive electrode 12 with respect to the lithium metal during charging is 3.7 V or higher and not higher than 4.0 V, the potential of the negative electrode 14 with respect to the lithium metal during charging becomes 0.4 V or lower, and 0. Not less than 1V. Therefore, the potential of the positive electrode 12 at the time of charging is increased, the charging capacity is increased, and a high capacity battery can be obtained. Further, the utilization factor of the negative electrode 14 becomes low, and there is no fear that lithium will be deposited on the negative electrode 14 even if it is rapidly charged.

Thus, according to the battery of this embodiment,
The potential for lithium metal when the positive electrode 12 is charged is 3.7 V or more and does not exceed 4.0 V, and the potential for lithium metal when the negative electrode 14 is charged is 0.4 V or less and more than 0.1 V. Since it is not made small, the charging capacity is improved and a high capacity battery can be obtained. Therefore, the operating time of the device can be lengthened. Further, by reducing the utilization rate of the negative electrode 14, rapid charging becomes possible.

In particular, the mass ratio of the negative electrode active material to the positive electrode active material (negative electrode active material mass / positive electrode active material mass) is 20/53.
When the ratio is 32/29 or less, the utilization rate of the negative electrode 14 can be reduced and the charge capacity can be increased.

[Second Embodiment] The second embodiment of the present invention relates to a secondary battery in which a disk-shaped positive electrode and a negative electrode are opposed to each other with an electrolyte interposed therebetween. Therefore,
In the present embodiment, description of the entire configuration will be omitted with reference to FIG. 1, and each component will be described using the same symbols as in FIG.

The positive electrode 12 contains, for example, a composite oxide containing lithium and at least one kind of transition metal as a positive electrode active material, and is composed of a conductive agent described later and, if necessary, a binder. . As the composite oxide containing lithium and at least one transition metal, for example, the lithium-cobalt composite oxide or the lithium-manganese composite oxide described in the first embodiment is used. Examples of the lithium-cobalt composite oxide include LiCoO ₂
Is mentioned. In particular, the general formula Li _x Mn _2-y MI _y O ₄
It is preferable to use the lithium-manganese composite oxide represented by the following because it is excellent in safety.

In addition to the lithium-cobalt composite oxide or the lithium-manganese composite oxide, the general formula Li
Other lithium composite oxide represented by _z MIIO ₂ may be contained. MII represents at least one kind of transition metal. z varies depending on the charging / discharging state of the battery, and is usually a value within the range of 0.05 ≦ z ≦ 1.10.

The conductive agent for the positive electrode 12 preferably contains flake graphite and amorphous carbon. The content of the flake graphite in the positive electrode 12 is 3% by mass or more and 7% by mass or less, and the mass ratio of the flake graphite to the amorphous carbon is flake graphite:
Amorphous carbon is preferably 6: 4 to 7: 2. Further, the content of scaly graphite in the positive electrode 12 is 4.0% by mass or more and 6.3% by mass or less, and the mass ratio of scaly graphite to amorphous carbon is scaly graphite: amorphous carbon = 4: 2. ~
It is more preferably 6.3: 2. This is because it is possible to improve the conductivity of the positive electrode 12, improve the discharge capacity particularly under heavy load, and improve the cycle characteristics. Further, as the flake graphite,
For example, graphite fine powder having an average particle diameter of 2 μm or more and 40 μm or less, and further preferably 2 μm or more and 6 μm or less is preferable. It can be easily handled and processed, and further, the positive electrode 12
This is because the conductivity of can also be increased.

The negative electrode 14 has, for example, a structure similar to that of the first embodiment. As the negative electrode active material,
It is preferable to use a carbonaceous material obtained by heat-treating an organic substance or a carbonaceous material self-sintered by carbonization by heat treatment. This is because the volume change during charge / discharge is small and the active material filling amount can be increased. As such a carbonaceous material, for example, JP-A-09-3
The one disclosed in JP-A-06492 is one in which two kinds of carbonaceous materials having different calcination temperatures from mesophase carbon as raw materials are mixed, granulated and molded, and then sintered in an inert gas. To be

Other components are the same as those in the first embodiment.

This secondary battery can be manufactured in the same manner as in the first embodiment.

This secondary battery operates as follows.

In this secondary battery, since flake graphite and amorphous carbon were used as the conductive agent of the positive electrode 12 and the contents thereof were adjusted as described above, the conductivity of the positive electrode 12 was increased, and particularly heavy load was applied. The discharge capacity can be improved and the cycle characteristics can be improved.

Thus, according to the battery of this embodiment,
The positive electrode 12 contains scaly graphite and amorphous carbon as a conductive agent, and the content of the scaly graphite in the positive electrode 12 is 3% by mass or more and 7% by mass or less, and the mass of scaly graphite and amorphous carbon. Since the ratio is flake graphite: amorphous carbon = 6: 4 to 7: 2, the conductivity of the positive electrode 12 can be increased, and in particular, the discharge capacity under heavy load can be improved. The cycle characteristics can be improved.
Therefore, it is possible to realize a coin-type battery that can be used as a main power source.

In particular, when the average particle diameter of the flake graphite is 2 μm or more and 40 μm or less, handling and processing can be facilitated and the discharge capacity can be improved.

Also in this embodiment, as described in the first embodiment, the potentials with respect to the lithium metal at the time of charging the positive electrode 12 and the negative electrode 14 may be adjusted. By doing so, the lithium-manganese composite oxide is used as the positive electrode active material, and the battery voltage is 3.6.
Even when the voltage is about V, a high capacity can be obtained.

[0046]

EXAMPLES Further, specific examples of the present invention will be described in detail with reference to FIG.

(Examples 1-1 to 1-7) First, LiNiO ₂ was used as the positive electrode active material, 90 parts by mass of this LiNiO ₂ , 5 parts by mass of graphite as a conductive agent and 2 parts by mass of amorphous carbon, A positive electrode mixture was prepared by mixing 3 parts by mass of polyvinylidene fluoride as a binder. Subsequently, the positive electrode mixture was pressure-molded to produce the positive electrode 12.

Further, as a negative electrode active material, Japanese Patent Laid-Open No. 09-30
The two types of carbonaceous materials having different calcination temperatures, which are made from mesophase carbon as disclosed in Japanese Patent No. 6492, are mixed, granulated and molded, and then sintered in an inert gas to form the negative electrode 14. Formed.

At that time, in Examples 1-1 to 1-7, the mass of the positive electrode active material and the mass of the negative electrode active material were changed as shown in Table 1 to adjust the designed positive electrode potential and the designed negative electrode potential. . The designed positive electrode potential and the designed negative electrode potential are the positive electrode 12 with respect to the lithium metal at the end of charging.
Alternatively, it is the potential of the negative electrode 14.

[0050]

[Table 1]

After that, a separator 15 made of a microporous polypropylene film having a thickness of 50 μm is prepared, the positive electrode 12, the separator 15 and the negative electrode 14 are laminated in this order, and after being inserted into the positive electrode can 11, the electrolytic solution 16 is injected. did. In the electrolytic solution 16, 1.0 mol of LiPF ₆ as an electrolyte salt was added to a solvent in which propylene carbonate and methyl ethyl carbonate were mixed at a mass ratio of propylene carbonate: methyl ethyl carbonate = 1: 1.
What was melt | dissolved by the content of / l was used. After that, the positive electrode can 11 and the negative electrode can 13 are caulked and sealed via a gasket 17, and the diameter is 20 mm and the height is 2. as shown in FIG.
A 5 mm coin type secondary battery was produced.

The discharge capacities of the obtained secondary batteries of Examples 1-1 to 1-7 were examined. At that time, the charging and discharging conditions are
A constant-voltage constant-current charge was performed at a current of 5 mA at 3.6 V for 24 hours, and then a constant-current discharge was performed up to 2.0 V at the same current as the charging. The obtained results are shown in Table 1 and FIG.

As can be seen from Table 1 and FIG. 2, there was a tendency that the discharge capacity increased as the designed negative electrode potential increased, showed a maximum value, and then decreased. That is, if the potential of the negative electrode 14 with respect to the lithium metal during charging is 0.4 V or less and not less than 0.1 V, it is further 0.35 V or less and not less than 0.15 V. It was found that the discharge capacity can be improved by doing so.

The mass ratio of the negative electrode active material to the positive electrode active material is 20/53 or more and 32/29 or less, and further 24/4.
It was also found that 6 or more and 31/30 or less is preferable.

Example 2 First, Li was used as a positive electrode active material.
A positive electrode mixture was prepared using the same materials as in Examples 1-1 to 1-7 except that CoO ₂ was used. At this time, L
The mixing amount of iCoO ₂ was changed in the range of 93 to 87 parts by mass, the mixing amount of graphite was changed in the range of 2 to 8 parts by mass, the amorphous carbon was 2 parts by mass, and the polyvinylidene fluoride was 3 parts by mass. did. The average particle size of graphite was 6 μm. Subsequently, this positive electrode mixture is added to 500 m
It was filled with a mass of g and preformed. After that, an expanded metal made of aluminum, which functions as a current collector, is placed and further pressure-molded to have an outer diameter of 15.5 mm and a height of 0.
A 7 mm positive electrode 12 was produced.

Further, a negative electrode 14 having an outer diameter of 15.6 mm, a height of 0.8 mm and a mass of 180 mg was formed in the same manner as in Examples 1-1 to 1-7.

After that, a secondary battery was manufactured in the same manner as in Examples 1-1 to 1-7.

Regarding the obtained secondary batteries, the discharge capacity and the closed circuit voltage at the end of discharge (Closed Circuit
Voltage; CCV) conversion resistance was examined. At this time, the charging / discharging conditions were a discharge current of 0.1 mA, a final voltage of 2 V, a charging voltage of 3 V, and a charging time of 24 hours. In addition, the closed circuit voltage measurement condition is a resistance of 100Ω for 5.0 seconds, and the closed circuit voltage conversion resistance value is an open circuit voltage (OC).
It was calculated as a percentage of the value obtained by subtracting the closed circuit voltage from V) with respect to the closed circuit voltage. The obtained results are shown in FIGS. 3 and 4, respectively. In FIG. 3, the discharge capacity ratio is expressed as a ratio with respect to the discharge capacity of 1 when the content of the flake graphite is 5 parts by mass.

As can be seen from FIG. 3, the discharge capacity monotonically increases as the blending ratio of the flake graphite increases.
The maximum value was shown at 0% by mass, and monotonically decreased when it exceeded 5.0% by mass. Further, as can be seen from FIG. 4, the resistance value in terms of closed circuit voltage at the end of discharge decreased as the blending ratio of the flake graphite increased. That is, the content of the flake graphite in the positive electrode 12 is 3.0 mass% or more and 7.0.
If the mass ratio is less than or equal to mass% and the mass ratio of scaly graphite to amorphous carbon is scaly graphite: amorphous carbon = 6: 4 to 7: 2, the discharge capacity is increased and the closed circuit voltage is improved due to the improvement in conductivity. It was found that the reduced resistance value was reduced and the cycle characteristics were improved. Further, the content of the flake graphite in the positive electrode 12 is 4.0% by mass or more and 6.3% by mass or less, and the mass ratio of the flake graphite to the amorphous carbon is flake graphite: amorphous carbon =
It was found that the ratio of 4: 2 to 6.3: 2 was more preferable.

(Examples 3-1 to 3-7) In producing the positive electrode 12, 5 parts by mass of graphite, which is flake graphite, and 2 parts by mass of amorphous carbon were used as a conductive agent, and flake graphite was used. A coin-type secondary battery was produced in the same manner as in Example 2 except that the average particle size of graphite was changed as shown in Table 2.

[0061]

[Table 2]

Regarding the obtained secondary batteries of Examples 3-1 to 3-7, the discharge capacity and the internal resistance value were examined in the same manner as in Example 2. The obtained results are also shown in Table 2. In Table 2, the discharge capacity ratio is expressed as a ratio with respect to the discharge capacity of 1 when the content of the flake graphite is 5 parts by mass.

As can be seen from Table 2, as the average particle size of the flake graphite increased, the discharge capacity increased, showed a maximum value, and then tended to decrease. In contrast to the discharge capacity, the internal resistance value decreases as the average particle size of the flake graphite increases, reaches a minimum value immediately after the discharge capacity reaches a maximum value, and then tends to increase. Was given. Therefore, it was found that the discharge capacity can be increased and the internal resistance value can be reduced when the average particle diameter of the flake graphite is within the range of 2 μm or more and 40 μm or less, and further within the range of 2 μm or more and 6 μm or less.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-mentioned embodiments and can be variously modified. For example, in the above-described embodiment, the coin-type secondary battery has been specifically described as an example, but in the first embodiment of the present invention, the positive electrode and the negative electrode are laminated with the electrolyte and the separator interposed therebetween, It is also applicable to a secondary battery having another shape such as a button type, a cylinder type or a square type having a wound electrode structure.

Furthermore, in the above-mentioned embodiments and examples, the secondary battery is specifically described, but the present invention can be similarly applied to other batteries such as a primary battery.

[0066]

As described above, according to the battery according to any one of claims 1 to 3, the potential of the positive electrode with respect to lithium metal during charging is 3.7 V or more, and 4. Since the potential is not higher than 0 V, the potential of the negative electrode with respect to the lithium metal during charging is 0.4 V or less, and not lower than 0.1 V, the charging capacity can be improved and a high capacity battery can be obtained. can get. Therefore, the operating time of the device can be lengthened. Also, by reducing the utilization rate of the negative electrode, rapid charging becomes possible.

Particularly, according to the battery of claim 2, the mass ratio of the negative electrode active material to the positive electrode active material (negative electrode active material mass /
Since the positive electrode active material mass) is set to 20/53 or more and 32/29 or less, the utilization rate of the negative electrode can be reduced and the charge capacity can be increased.

According to the battery of any one of claims 4 to 7, the positive electrode contains scaly graphite and amorphous carbon as a conductive agent, and the mass ratio of the scaly graphite in the positive electrode is 3 The mass ratio is from 7% by mass to 7% by mass, and the mass ratio of the scaly graphite to the amorphous carbon is scaly graphite: amorphous carbon = 6: 4.
Since it is set to 7: 2, the conductivity of the positive electrode can be increased, the discharge capacity can be improved especially under heavy load, and the cycle characteristics can be improved. Therefore, it is possible to realize a coin-type battery that can be used as a main power source.

In particular, according to the battery of the sixth aspect, the average particle diameter of the flake graphite is set to 2 μm or more and 40 μm or less, so that handling and processing can be facilitated.

Further, in particular, according to the battery of claim 7, the potential with respect to the lithium metal at the time of charging the positive electrode is 3.7 V or more and does not become larger than 4.0 V, and the lithium metal at the time of charging the negative electrode is Since the potential of the lithium-manganese composite oxide is set to 0.4 V or less and not lower than 0.1 V, a high capacity is obtained even when the lithium-manganese composite oxide is used as the positive electrode active material and the battery voltage is set to about 3.6 V. Can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a secondary battery according to a first exemplary embodiment and a second exemplary embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a negative electrode potential with respect to lithium and a discharge capacity in the secondary battery shown in FIG. 1 according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the mass ratio of the flake graphite contained in the conductive agent to the positive electrode and the discharge capacity in the secondary battery shown in FIG. 1 according to the second embodiment of the present invention. .

FIG. 4 is a characteristic of the secondary battery shown in FIG. 1 according to the second embodiment of the present invention, showing the relationship between the mass ratio of the flake graphite contained in the conductive agent to the positive electrode and the closed circuit voltage conversion resistance value. It is a figure.

FIG. 5 is a characteristic diagram regarding a positive electrode potential, a negative electrode potential, and a battery voltage in a general lithium ion secondary battery.

FIG. 6 is a characteristic diagram showing a relationship between a charging voltage and a charge / discharge capacity and charge / discharge efficiency in a general lithium ion secondary battery.

[Explanation of symbols]

11 ... Positive electrode can, 12 ... Positive electrode, 13 ... Negative electrode can, 14 ... Negative electrode, 15 ... Separator, 16 ... Electrolyte, 17 ... Gasket

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshinori Atsumi             1 Shimo-Sugishita, Takakura, Hiwada-cho, Koriyama City, Fukushima Prefecture             1 Sony Fukushima Co., Ltd. (72) Inventor Kazuhiro Iwasa             1 Shimo-Sugishita, Takakura, Hiwada-cho, Koriyama City, Fukushima Prefecture             1 Sony Fukushima Co., Ltd. (72) Inventor Yasuo Ota             1 Shimo-Sugishita, Takakura, Hiwada-cho, Koriyama City, Fukushima Prefecture             1 Sony Fukushima Co., Ltd. F term (reference) 5H029 AJ03 AK03 AK18 AL02 AL06                       AL07 AL16 AL18 AM03 AM04                       AM05 AM07 AM16 BJ03 CJ02                       CJ08 DJ08 DJ16 EJ04 HJ01                       HJ05 HJ18                 5H050 AA08 BA17 CA08 CA09 CA29                       CB07 CB08 CB20 CB29 DA02                       DA10 EA09 FA17 GA02 GA10                       HA01 HA05 HA18

Claims (7)

[Claims] 1. A battery comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte, wherein the positive electrode contains lithium-nickel composite oxide and lithium-manganese as the positive electrode active material. A potential for lithium metal at the time of charging the positive electrode is 3.7 V or more and not higher than 4.0 V, including at least one kind of complex oxide, and a potential for lithium metal at the time of charging the negative electrode. Is a battery that is 0.4 V or less and does not become less than 0.1 V. 2. The mass ratio of the negative electrode active material to the positive electrode active material (negative electrode active material mass / positive electrode active material mass) is 20.
The battery according to claim 1, which is / 53 or more and 32/29 or less. 3. The battery according to claim 1, wherein the negative electrode contains a negative electrode material capable of inserting and extracting lithium as a negative electrode active material. 4. A battery in which a disk-shaped positive electrode and a negative electrode are arranged to face each other with an electrolyte interposed therebetween, wherein the positive electrode contains at least one of lithium and a positive electrode active material.
Along with containing a complex oxide containing a kind of transition metal, containing scaly graphite and amorphous carbon as a conductive agent, the content of the scaly graphite in the positive electrode is 3% by mass or more and 7% by mass or less. The battery is characterized in that the mass ratio of the scaly graphite to the amorphous carbon is scaly graphite: amorphous carbon = 6: 4 to 7: 2. 5. The positive electrode contains a lithium-manganese composite oxide as a positive electrode active material, and the negative electrode as a negative electrode active material is a carbonaceous material obtained by heat-treating an organic material and self-calcination by carbonization by heat treatment. The battery according to claim 4, comprising at least one of the bonded carbonaceous materials. 6. The scaly graphite has an average particle diameter of 2 μm.
The battery according to claim 4, wherein the battery has a thickness of 40 μm or less. 7. The potential of the positive electrode with respect to lithium metal during charging is 3.7 V or higher and not higher than 4.0 V, and the potential of the negative electrode with respect to lithium metal during charging is 0.4 V or lower. The battery according to claim 4, wherein the battery does not become lower than 0.1 V.