JP3140880B2 - Lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery using a negative electrode obtained by mixing copper oxide and a binder with graphite capable of intercalating lithium.

[0002]

2. Description of the Related Art With the miniaturization and power saving of electronic devices,
A secondary battery using an alkali metal such as lithium has attracted attention. When an alkali metal such as lithium is used alone for the negative electrode, repetition of charge and discharge, that is, a process of dissolving and depositing the alkali metal, generates dendrite (dendritic crystal) on the surface where the metal is dissolved and deposited, and grows. Separation
There is a problem that a short circuit inside the battery is induced by penetrating through the battery and coming into contact with the positive electrode. It has been found that when an alkali metal alloy is used for a negative electrode for a secondary battery instead of an alkali metal, the generation of dendrites is suppressed and the charge / discharge cycle characteristics are improved as compared with the case of a single battery. However, the use of the alloy does not completely prevent the generation of dendrite, and may cause a short circuit inside the battery. In recent years, instead of using a dissolution-precipitation process or a dissolution-precipitation-solid diffusion process of a metal such as an alkali metal or an alloy thereof, carbon using an absorption-release process of an alkali metal ion has been used. Organic materials such as conductive polymers have been developed. As a result, the generation of dendrite generated when an alkali metal or an alloy thereof is used does not occur in principle, and the problem of a short circuit inside the battery has been drastically reduced.

[0003] Since carbon is chemically stable and can be doped with both an electron donating substance and an electron accepting substance, it is a promising material as an electrode, particularly as an electrode for a battery.

[0004] When carbon is used as the negative electrode active material, the amount of lithium inserted between carbon layers is 1 lithium atom per 6 carbon atoms, that is, C ₆ Li. The capacity per weight is 372 mAh / g.
Carbon has a wide range of structures from what is called amorphous carbon to graphite, and the size and arrangement of carbon hexagonal planes vary depending on starting materials, production methods and the like. Examples of carbon materials conventionally used as negative electrode active materials include, for example, JP-A Nos. 62-90863, 62-122066, 63-213267, and 1-2.
JP-A-04361, JP-A-2-82466, JP-A-3-252053, JP-A-3-285273, JP-A-3-289068 and the like. With these carbons, none of the above-mentioned theoretical capacities are reached, and even if they have a certain large capacity, the potential at the time of deintercalation of lithium increases linearly and actually constitutes a battery system. In some cases, a sufficient capacity is not exhibited in a potential range that can be used, and a negative electrode having a satisfactory negative electrode capacity for manufacturing a battery cannot be manufactured. Also, when producing an electrode, the true density of the carbon material is also required,
When considering the density per unit volume, the bulk density is an important factor. The bulk density governs the shape of the carbon particles,
In the examples of JP-A-62-90863, the fibrous carbon disclosed in JP-A-2-82466, JP-A-3-285273, and JP-A-3-289068 increases the capacity density per unit volume. This is difficult, and none of these fibrous carbons reach the above-mentioned theoretical capacity, and a negative electrode having a satisfactory negative electrode capacity in manufacturing a battery cannot be manufactured. Also, JP-A-63-
Although pyrolytic carbon produced by a gas phase method as shown in 24555 shows high charge / discharge stability, it is difficult to produce a thick-film electrode by this method, and it is difficult to obtain a high-capacity electrode.

On the other hand, R. Fong, U. Sacken, and J.
As described in R. Dahn, J. Electrochem. Soc., 137, 2009 (1990), when graphite is used as the negative electrode active material, although the theoretical discharge capacity is obtained, it is a small current measurement. It is not satisfactory for practical use. Further, as disclosed in JP-A-4-112455, JP-A-4-115457, JP-A-4-115458, JP-A-4-237971, JP-A-5-28996, etc. as those using a graphite material as a negative electrode active material, Since the above-mentioned theoretical capacity has not been reached, a negative electrode which is satisfactory as a negative electrode capacity in manufacturing a battery cannot be manufactured.

As disclosed in JP-A-5-21065, a chalcogen compound having an average voltage of 2 V (Li / Li ⁺ ) or less and a carbonaceous material capable of inserting and desorbing lithium ions are used. However, there is a problem that the charge / discharge voltage is low and the energy density is reduced.

[0007] As disclosed in Japanese Patent Application Laid-Open No. H4-184863, a metal (nickel, copper) film is formed on a carbon material.
By using a mixed anode of carbon and a metal (a metal not alloyed with at least one kind of lithium) as in 259768, the cycle characteristics can be improved, and the high-rate discharge after leaving at high temperature can be improved. No fundamental improvement in anode capacity can be expected.

As disclosed in JP-A-3-216960, by forming lithium on the surface of a carbon body so as not to block a hole, a large current can be taken out and a secondary battery having improved cycle life and safety can be obtained. A battery can be obtained, and the use of a negative electrode in which a carbonaceous material is impregnated with an alloy capable of forming an alloy with an active material as described in JP-A-4-39864 has a large electrode capacity, excellent charge / discharge cycle characteristics, and self-discharge. A secondary battery with improved characteristics can be obtained,
There is a problem that the number of steps in manufacturing the electrode increases.

As disclosed in Japanese Patent Application Laid-Open No. 4-179049, the use of a composite negative electrode of a conductive polymer and a metal and / or a carbon-based material makes it possible to provide a negative electrode for batteries that is flexible and has a long cycle life. There's a problem.

[0010]

SUMMARY OF THE INVENTION As described above,
Even if various carbon materials and graphite materials are used for the negative electrode active material, the theoretical capacity (372 mAh / g) is not reached, and a negative electrode having a satisfactory negative electrode capacity for manufacturing a battery cannot be manufactured. However, although the graphite material can basically charge and discharge the theoretical capacity, there is a problem that the charge and discharge current value used at that time is not a practically usable current value. In addition, the reaction of inserting and removing lithium ions has an average voltage of 2 V (Li / Li
⁺ ) A negative electrode mixed with a chalcogen compound and a carbonaceous material capable of inserting and removing lithium ions is used, but the charge / discharge voltage is low and the energy density is low. In the case of a composite anode with a metal that does not form an anode, it is not possible to bring about a fundamental improvement in the anode capacity, and in a composite anode in which carbon is coated with lithium or a metal that forms an alloy with lithium, the number of steps in electrode production increases. There is a problem in the charge / discharge capacity of a composite negative electrode of a conductive polymer and a metal and / or a carbon-based material.

In view of the above-mentioned circumstances, the present invention provides a high-capacity electrode by providing an electrode obtained by mixing copper oxide and a binder with graphite capable of intercalating and deintercalating lithium. It is an object of the present invention to provide a graphite-mixed negative electrode that can reduce the number of steps in production, and a high-capacity, high-voltage lithium secondary battery.

[0012]

According to the present invention, a positive electrode,
In a battery comprising a negative electrode and a non-aqueous ion conductor,
The negative electrode is made of graphite capable of intercalating and deintercalating lithium ions as a main component of a negative electrode active material, and furthermore, a lithium secondary battery that is an electrode in which copper oxide and a binder are present in this electrode. Provided.

The negative electrode of the present invention is produced by mixing graphite, which is capable of intercalating and deintercalating lithium ions as a main component of the negative electrode active material, copper oxide, and a binder, followed by molding. . At this time, the negative electrode and the negative electrode current collector can be integrally formed using the negative electrode current collector.

Graphite as a main component of the negative electrode active material used in the present invention has an average spacing (d ₀₀₂ ) of (002) planes by a wide angle X-ray diffraction method of 0.335 to 0.340 nm,
The crystallite thickness (Lc) in the (002) plane direction is 10 nm or more, and the crystallite thickness (La) in the (110) plane direction is 10 nm.
The above materials are used, and a high-capacity electrode can be obtained by using these materials. Factors affecting the capacity and charge / discharge potential include physical properties related to the layered structure of carbon. Physical properties related to the layered structure of carbon include (00
2) The plane spacing (d ₀₀₂ ) of the planes, that is, the interlayer distance, and the crystallite size are present. Since the potential at the time of deintercalation of lithium becomes closer to the potential of lithium by increasing the degree of crystallinity, it is possible to expect to obtain a higher capacity carbon body electrode. Therefore, when assuming the usable battery capacity when assembling as a lithium secondary battery, the average spacing (d ₀₀₂ ) of the (002) plane by the X-ray wide-angle diffraction method is 0.335 to 0.340 nm. Preferably, there is. (002) Crystallite thickness in the plane direction (L
In c), when the thickness is 10 nm or less, the crystallinity is poor, so that when assembled as a lithium secondary battery, the usable battery capacity becomes small, which is not practical. (110)
When the crystallite thickness (La) in the in-plane direction is less than 10 nm, the crystallinity is poor. Therefore, when assembled as a lithium secondary battery, the usable battery capacity becomes small, which is not practical.

The graphite used as the main component of the negative electrode active material used in the present invention was prepared by argon laser Raman.
The intensity ratio of the peak near 1360 cm -1 to the peak near 580 cm -1, that is, the R value is preferably 0.4 or less. If it is larger than 0.4, the crystallinity will be low and the potential at the time of deintercalation of lithium will be higher than the potential of lithium, so the battery capacity that can be used when assembled as a lithium secondary battery is Small and impractical.

Examples of the graphite that can be used include artificial graphite obtained from easily graphitizable carbon such as natural graphite, quiche graphite, petroleum coke or coal pitch coke, or expanded graphite, which satisfies the above physical properties. Graphites, and as shapes, spherical, flaky,
Any of fibrous or crushed products thereof may be used, but spherical, flaky or crushed products thereof are preferred.

When graphite is used as the negative electrode, the graphite preferably has a particle size of 80 μm or less. The particle size is a value obtained as a particle size having a peak in a particle size distribution obtained by a particle size distribution measurement on a volume basis. 80
When graphite having a particle size larger than μm is used, the contact area with the electrolytic solution becomes smaller, so that diffusion of lithium in the particles,
Problems such as a decrease in the number of reaction sites occur, and problems arise in charging and discharging with a large current.

As the copper oxide mixed in the negative electrode, a simple substance of cuprous oxide and cupric oxide or a mixture thereof can be used, but cupric oxide is more preferable in terms of improvement in charge / discharge capacity. preferable. The ratio of copper oxide contained in the negative electrode depends on the type and particle size of graphite or copper oxide, but the weight ratio of graphite to copper oxide is 9.8: 0.2 to 0.2%.
The ratio is preferably 4: 6. Especially 9.8: 0.2 ~
It is preferably in the range of 6: 4. When the ratio is smaller than 9.8: 0.2, the mixed effect is not remarkably exhibited. When the ratio is larger than 4: 6, the number of reaction sites of lithium ions decreases during charging and discharging of graphite, and when assembled as a lithium secondary battery, The usable battery capacity is small and not practical.

The negative electrode is formed by mixing the above-described graphite, copper oxide, and a binder. As the binder, a fluorine-based polymer such as polytetrafluoroethylene and polyvinylidene fluoride, a polyolefin-based polymer such as polyethylene and polypropylene, and synthetic rubbers can be used, but are not limited thereto. The weight ratio of the mixture of graphite and copper oxide to the binder was 99: 1.
７０70: 30. 70:30 binder
If it is larger, the resistance or polarization of the electrode becomes large and the discharge capacity becomes small, so that a practical lithium secondary battery cannot be manufactured. On the other hand, if the binder is smaller than 90: 1, the binding ability is lost, and it is difficult to manufacture the battery due to the falling off of the active material and the decrease in mechanical strength. In the preparation of the negative electrode, it is preferable to perform a heat treatment at a temperature around the melting point of each binder in order to enhance the binding property.

A current collector is required to collect current from the negative electrode. Examples of the current collector include a metal foil, a metal mesh, and a three-dimensional porous body. As the metal used for the current collector, a metal which is unlikely to alloy with lithium is preferable in terms of mechanical strength when cycles are repeated. In particular, iron, nickel, cobalt, copper, titanium, vanadium, chromium, and manganese alone or alloys thereof are preferable.

As the ion conductor, for example, an organic electrolyte, a polymer solid electrolyte, an inorganic solid electrolyte, a molten salt, or the like can be used, and among them, the organic electrolyte can be preferably used. As the solvent for the organic electrolyte, propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, esters such as γ-butyrolactone, tetrahydrofuran, substituted tetrahydrofuran such as 2-methyltetrahydrofuran, dioxolane, diethyl ether , Dimethoxyethane, diethoxyethane,
Ethers such as methoxyethoxyethane, dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl formate, methyl acetate and the like;
Used as one or more mixed solvents. Examples of the electrolyte include lithium salts such as lithium perchlorate, lithium borofluoride, lithium phosphofluoride, lithium arsenide hexafluoride, lithium trifluoromethanesulfonate, lithium halide, lithium aluminate, and the like. A mixture of two or more types is used. An electrolyte is prepared by dissolving the electrolyte in the solvent selected above. The solvent and the electrolyte used when preparing the electrolytic solution are not limited to those listed above.

As the positive electrode in the lithium secondary battery of the present invention, LiCoO ₂ , LiNiO _2, and L
ixMyNzO ₂ (where M is any of Fe, Co, and Ni, and N represents a transition metal, a 4B group, or a 5B group metal), LiMn ₂ O _4, and LiMn ₂ -xNyO ₄ (where N is An oxide containing lithium (such as a transition metal, a 4B group metal, or a 5B group metal) is used as a positive electrode active material, and a conductive material, a binder, and, in some cases, a solid electrolyte are mixed with the positive electrode active material. You. This mixing ratio depends on the active material 1
The conductive material can be 5 to 50 parts by weight and the binder can be 1 to 30 parts by weight with respect to 00 parts by weight. As the conductive material, carbons such as carbon black (acetylene black, thermal black, channel black, etc.), graphite powder, metal powder, and the like can be used, but are not limited thereto. As the binder, a fluorine-based polymer such as polytetrafluoroethylene or polyvinylidene fluoride, a polyolefin-based polymer such as polyethylene or polypropylene, or a synthetic rubber can be used, but is not limited thereto. If the conductive material is less than 5 parts by weight or the binder is more than 30 parts by weight, the resistance or polarization of the electrode increases and the discharge capacity decreases, so that a practical lithium secondary battery cannot be manufactured. When the amount of the conductive material is more than 50 parts by weight (parts by weight vary depending on the type of the conductive material to be mixed), the amount of the active material contained in the electrode decreases, so that the discharge capacity as the positive electrode decreases. When the binder is smaller than 1 part by weight, the binding ability is lost. When the binder is larger than 30 parts by weight, as in the case of the conductive material,
This is not practical because the amount of active material contained in the electrode decreases, and, as described above, the resistance or polarization of the electrode increases and the discharge capacity decreases. In producing the positive electrode, it is preferable to perform a heat treatment at a temperature around the melting point of each binder in order to improve the binding property.

[0023]

The negative electrode according to the present invention, that is, an electrode obtained by mixing copper oxide and a binder with graphite capable of intercalating / deintercalating lithium has a high capacity. This is because a composite oxide of lithium and copper that progresses reversibly is formed in the electrochemically reduced copper oxide. Also, the number of steps in electrode production can be reduced as compared with a composite negative electrode in which carbon is coated with lithium or a metal forming an alloy with lithium. Further, a negative electrode in which a high-capacity, mixed reaction of a chalcogen compound having an average voltage of 2 V (Li / Li +) or less for lithium ion insertion and desorption and a carbonaceous substance capable of lithium ion insertion and desorption is used. Since a lower potential of the negative electrode can be used as compared with a battery using, a lithium secondary battery with a high battery voltage can be provided. Therefore, the lithium secondary battery using the negative electrode according to the present invention can provide an excellent lithium secondary battery that solves the above problems.

[0024]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples.

Incidentally, a method of measuring the crystallite size (Lc, La) by the X-ray wide-angle diffraction method is a known method, for example, "Carbon Materials Experimental Techniques 1 p55-63, edited by the Society of Carbon Materials (Science and Technology Corporation). And the method described in JP-A-61-111907. Further, 0.9 was used as the shape factor K for obtaining the size of the crystallite. Also,
The particle size is measured using a laser diffraction type particle size distribution meter,
It was determined as a particle size having a peak in the particle size distribution.

Example 1 Preparation of negative electrode As a main negative electrode active material, natural graphite produced in Madagascar (flaky, particle size 11 μm, d ₀₀₂ 0.337 nm, Lc 2
7 nm, La is 17 nm, R value is 0, specific surface area is 8 m ² /
g) and commercially available cupric oxide (particle diameter 27 μm)
Are mixed in a mortar at a weight ratio of 9.5: 0.5, a nonionic dispersant is added, and polytetrafluoroethylene (after drying, combined with graphite and cupric oxide, polytetrafluoroethylene) is added. The weight ratio with ethylene is 87:13).
It was applied on both sides on a copper foil current collector. This is dried at 60 ° C,
After heat treatment at 240 ° C., pressing was performed, followed by drying under reduced pressure at 200 ° C. to remove water, and used as a negative electrode. This negative electrode had a surface area of 8 cm ² and an electrode thickness of 126 μm.
(The thickness of the current collector is 50 μm).

Evaluation of Negative Electrode Current was collected from the copper current collector with a lead wire, and used as an electrode for evaluation. For evaluation, a three-electrode method was used, and lithium was used as a counter electrode and a reference electrode. The electrolytic solution is obtained by dissolving 1 mol / l of lithium perchlorate in a 1: 1 mixed solvent of ethylene carbonate and diethyl carbonate. The charge / discharge test is
Initially charge to 0 V at a current density of 30 mA / g,
Subsequently, discharge was performed to 2.5 V at the same current. After the second time, charge and discharge were repeated in the same potential range and current density, and the negative electrode was evaluated by discharge capacity.

As a result, the discharge capacity at the second cycle was 398 mAh / g of carbon, and the discharge capacity at the 20th cycle was 385 mAh / g of carbon.

Example 2 Natural graphite from Madagascar was used as a main negative electrode active material.
This was mixed with a commercially available cuprous oxide (particle diameter: 34 μm) at a weight ratio of 9.6: 0.4, and a negative electrode was produced by the method described in Example 1. The surface area of the prepared negative electrode is 8c
m ² , and the thickness is 139 μm (the thickness of the current collector is 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 373 mAh / g of carbon, and the discharge capacity at the 20th cycle was 359 mAh / g of carbon.

Example 3 Expanded graphite (flaky, particle size 8 μm,
d ₀₀₂ is 0.337 nm, Lc is 17 nm, La is 12
nm, the R value was 0.1, the specific surface area was 9 m ² / g), and this was mixed with a sieved commercial cupric oxide (particle size: 15 μm) at a weight ratio of 9: 1, and described in Example 1. A negative electrode was manufactured by the method described above. The produced negative electrode has a surface area of 8 cm ² ,
The thickness is 81 μm (the thickness of the current collector is 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity in the second cycle was 467 mAh / g of carbon, and the discharge capacity in the 20th cycle was 412 mAh / g of carbon.

Example 4 Expanded graphite (flaky, particle size 8 μm,
d ₀₀₂ is 0.337 nm, Lc is 17 nm, La is 12
nm, the R value is 0.1, the specific surface area is 9 m ² / g), and the weight ratio of this to commercially available cuprous oxide (particle size: 34 μm) is 9.
6: 0.4, and a negative electrode was prepared by the method described in Example 1. The produced negative electrode had a surface area of 8 cm ² and a thickness of 125 μm (the thickness of the current collector was 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 427 mAh / g of carbon, and the discharge capacity at the 20th cycle was 398 mAh / g of carbon.

Comparative Example 1 A negative electrode was produced in the same manner as in Example 1 except that only natural graphite produced in Madagascar was used. The produced negative electrode had a surface area of 8 cm ² and a thickness of 130 μm (the thickness of the current collector was 50 μm).
m).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 349 mAh / g of carbon, and the discharge capacity at the 20th cycle was 338 mAh / g of carbon.

Table 1 shows the results of Examples 1 to 4 and Comparative Example 1. From this, it was found that mixing graphite with copper oxide increased the discharge capacity as a negative electrode.

[0042]

[Table 1]

Example 5 Expanded graphite (flaky, particle size 17 μm) was used as the main negative electrode active material.
m and d ₀₀₂ are 0.337 nm, Lc is 22 nm, La is 15 nm, R value is 0.1, specific surface area is 9 m ² / g),
Commercial cupric oxide sieved with this (particle size 52 μm)
Were mixed at a weight ratio of 9.4: 0.6, and a negative electrode was produced by the method described in Example 1. The produced negative electrode had a surface area of 8 cm ² and a thickness of 178 μm (the thickness of the current collector was 50 μm).
m).

The negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 378 mAh / g of carbon, and the discharge capacity at the 20th cycle was 365 mAh / g of carbon.

Example 6 Artificial graphite (flaky, particle size 35 μm) was used as the main negative electrode active material.
m and d ₀₀₂ are 0.336 nm, Lc is 22 nm, La is 13 nm, R value is 0, specific surface area is 4 m ² / g), and this is weighed with commercially available cupric oxide (particle size: 23 μm). The mixture was mixed at a ratio of 9.5: 0.5 to produce a negative electrode by the method described in Example 1. The produced negative electrode has a surface area of 8
cm ² , thickness 135 μm (current collector thickness 50 μm)
It is.

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 370 mAh / g of carbon, and the discharge capacity at the 20th cycle was 352 mAh / g of carbon.

Example 7 Artificial graphite (spherical, particle size 6 μm, d
₀₀₂ is 0.339 nm, Lc is 25 nm, La is 13 n
The m and R values were 0.4, the specific surface area was 8 m ² / g), and this was mixed with a sieved commercial cupric oxide (particle size: 15 μm) at a weight ratio of 9.2: 0.8. A negative electrode was prepared by the method described in Example 1. The surface area of the prepared negative electrode is 8c
m ² , and the thickness is 92 μm (the thickness of the current collector is 50 μm).

This negative electrode was described in Example 1 except that the electrolyte was prepared by dissolving 1 mol / l lithium perchlorate in a 2: 1: 2 mixed solvent of ethylene carbonate, propylene carbonate, and diethyl carbonate. Was evaluated in the manner described.

As a result, the discharge capacity at the second cycle was 369 mAh / g of carbon, and the discharge capacity at the 20th cycle was 355 mAh / g of carbon.

Comparative Example 2 Mesocarbon microbeads carbonized at 1000 ° C. (spherical, particle diameter 6 μm, d ₀₀₂ was 0.3
49 nm, Lc is 1.3 nm, La is not calculable, R value is 1.3, specific surface area is 1 m ² / g), and this is weighed with commercially available cupric oxide (particle size: 23 μm). 9.
3: 0.7 was mixed, and a negative electrode was produced by the method described in Example 1. The surface area of the produced negative electrode was 8 cm ² , and the thickness was 105 μm (the thickness of the current collector was 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 135 mAh / g of carbon, and the discharge capacity at the 20th cycle was 122 mAh / g of carbon.

Table 1 shows the results of Examples 1 to 7 and Comparative Example 2. From this, it was found that a high discharge capacity was obtained in the case of a mixture of graphite and copper oxide.

Example 8 Artificial graphite (flaky, particle size: 77 μm) was used as the main negative electrode active material.
m, d ₀₀₂ is 0.337 nm, Lc is 26 nm, La is 14 nm, R value is 0.1, specific surface area is 2 m ² / g),
Commercial cupric oxide sieved with this (23μm particle size)
Were mixed at a weight ratio of 9.5: 0.5, and a negative electrode was produced by the method described in Example 1. The produced negative electrode had a surface area of 8 cm ² and a thickness of 205 μm (the current collector had a thickness of 50 μm).
m).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 378 mAh / g of carbon, and the discharge capacity at the 20th cycle was 365 mAh / g of carbon.

Comparative Example 3 Artificial graphite (flaky, particle size: 117 μm) was used as the main negative electrode active material.
m and d ₀₀₂ are 0.337 nm, Lc is 25 nm, La is 17 nm, R value is 0.1, specific surface area is 1 m ² / g),
Commercial cupric oxide sieved with this (23μm particle size)
Were mixed at a weight ratio of 9.4: 0.6, and a negative electrode was produced by the method described in Example 1. The produced negative electrode had a surface area of 8 cm ² and a thickness of 278 μm (the thickness of the current collector was 50 μm).
m).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 305 mAh / g of carbon, and the discharge capacity at the 20th cycle was 288 mAh / g of carbon.

Table 1 shows the results of Examples 1 to 8 and Comparative Example 3. This proved that graphite having a particle size of 80 μm or less was good.

Example 9 Natural graphite produced in Madagascar was used as a main negative electrode active material, and this was mixed with a commercially available cupric oxide (particle diameter: 27 μm) in a mortar at a weight ratio of 9.5: 0.5. A nonionic dispersant is added, and a dispersion liquid of polytetrafluoroethylene (the weight ratio of the mixture of graphite and cupric oxide after drying and polytetrafluoroethylene is 76:24) is added. Was applied to a nickel three-dimensional porous current collector, and the paste was applied to the holes. This was dried at 60 ° C., heat treated at 240 ° C., pressed, and further dried at 200 ° C. under reduced pressure to remove moisture, and used as a negative electrode. This negative electrode has a surface area of 4c.
m ² , and the thickness of the electrode is 378 μm.

The current was collected from the nickel three-dimensional porous current collector of the negative electrode with a lead wire, and used as an electrode for evaluation. Then, the negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 363 mAh / g of carbon, and the discharge capacity at the 20th cycle was 348 mAh / g of carbon.

Comparative Example 4 After drying, a negative electrode was prepared in the same manner as in Example 9 except that the weight ratio of graphite and cupric oxide to polytetrafluoroethylene was changed to 62:38. did. The surface area of the produced negative electrode was 4 cm ² , and the thickness was 405 μm.

This negative electrode was evaluated by the method described in Example 9.

As a result, the discharge capacity at the second cycle was 285 mAh / g of carbon, and the discharge capacity at the 20th cycle was 253 mAh / g of carbon.

Example 10 After drying, except that the weight ratio of graphite and cupric oxide to polytetrafluoroethylene was 97: 3,
A negative electrode was produced by the method described in Example 1. The produced negative electrode had a surface area of 8 cm ² and a thickness of 115 μm (the thickness of the current collector was 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 395 mAh / g of carbon, and the discharge capacity at the 20th cycle was 361 mAh / g of carbon.

Comparative Example 5 The method described in Example 1 was repeated, except that the weight ratio of the mixture of graphite and cupric oxide to polytetrafluoroethylene after drying was 99.5: 0.5. When the negative electrode was manufactured, the negative electrode was separated from the current collector.

Table 2 shows the results of Examples 9 and 10 and Comparative Examples 4 and 5. From these and Examples 1 to 8, the weight ratio of the combination of graphite and cupric oxide to the binder was 99: 1 to 7
0:30 has been found to be optimal.

[0074]

[Table 2]

Example 11 As a main negative electrode active material, artificial graphite (flaky, particle size 7 μm,
d ₀₀₂ is 0.336 nm, Lc is 22 nm, La is 13
nm, the R value is 0.1, and the specific surface area is 10 m ² / g).
This was mixed with a commercially available cupric oxide (particle diameter 27 μm) at a weight ratio of 9.1: 0.9 in a mortar, and N, N
-Polyvinylidene fluoride dissolved in dimethylformamide (weight ratio of N, N-dimethylformamide to polyvinylidene fluoride is 1.5: 0.05)
Into a paste. At this time, the mixture of graphite and cupric oxide and polyvinylidene fluoride was mixed so that the weight ratio after drying was 91: 9. This paste was applied on both surfaces of a stainless steel foil current collector. This is 6
After drying at 5 ° C., heat treatment at 155 ° C., pressing, and drying under reduced pressure at 160 ° C. to remove moisture, the negative electrode was used. This negative electrode has a surface area of 8 cm ² and an electrode thickness of 113 μm.

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 383 mAh / g of carbon, and the discharge capacity at the 20th cycle was 362 mAh / g of carbon.

Example 12 As a main negative electrode active material, artificial graphite (flaky, particle size 7 μm,
d ₀₀₂ is 0.336 nm, Lc is 22 nm, La is 13
nm, the R value is 0.1, and the specific surface area is 10 m ² / g).
This was mixed with a commercially available cupric oxide (particle diameter 27 μm) at a weight ratio of 9.2: 0.8 in a mortar, and a polyethylene powder was added to the mixture with graphite and cupric oxide; The mixture was mixed so that the weight ratio with polyethylene was 89:11, and the mixture was applied to the pores of the nickel three-dimensional porous current collector.
This was pressed by applying heat of 125 ° C., and then dried under reduced pressure at 110 ° C. to remove moisture, and used as a negative electrode. This negative electrode has a surface area of 4 cm ² and an electrode thickness of 33.
4 μm.

This negative electrode was evaluated by the method described in Example 9.

As a result, the discharge capacity at the second cycle was 368 mAh / g of carbon, and the discharge capacity at the 20th cycle was 351 mAh / g of carbon.

Example 13 Expanded graphite (flaky, particle size 8 μm,
d ₀₀₂ is 0.337 nm, Lc is 17 nm, La is 12
nm, R value: 0.1, specific surface area: 9 m ² / g), and a commercially available cupric oxide (particle size: 15 μm) sieved with a weight ratio of 8: 2 (graphite / (graphite + copper oxide)) = 0.8), and a negative electrode was produced by the method described in Example 1. The produced negative electrode has a surface area of 8 cm ² and a thickness of 104 μm.
m (the thickness of the current collector is 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 408 mAh / g of carbon, and the discharge capacity at the 20th cycle was 398 mAh / g of carbon.

Example 14 A negative electrode was prepared in the same manner as in Example 13 except that commercially available sieved cupric oxide (particle size: 23 μm) was used.
The produced negative electrode had a surface area of 8 cm ² and a thickness of 88 μm (the thickness of the current collector was 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 403 mAh / g of carbon, and the discharge capacity at the 20th cycle was 395 mAh / g of carbon.

Example 15 A negative electrode was produced in the same manner as in Example 13 except that commercially available cupric oxide (particle size: 35 μm) sieved was used.
The produced negative electrode had a surface area of 8 cm ² and a thickness of 126 μm.
(The thickness of the current collector is 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 402 mAh / g of carbon, and the discharge capacity at the 20th cycle was 397 mAh / g of carbon.

Example 16 The weight ratio between expanded graphite and cupric oxide (particle size 23 μm) was 9.8: 0.2 (graphite / (graphite + copper oxide) = 0.98).
A negative electrode was produced in the same manner as in Example 13 except that the above-mentioned conditions were satisfied. The produced negative electrode had a surface area of 8 cm ² and a thickness of 86 μm.
m (the thickness of the current collector is 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 384 mAh / g of carbon, and the discharge capacity at the 20th cycle was 361 mAh / g of carbon.

Example 17 The weight ratio of expanded graphite to cupric oxide (particle size 23 μm) was 9.5: 0.5 (graphite / (graphite + copper oxide) = 0.95).
A negative electrode was produced in the same manner as in Example 13 except that the above-mentioned conditions were satisfied. The produced negative electrode had a surface area of 8 cm ² and a thickness of 97 μm.
m (the thickness of the current collector is 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 393 mAh / g of carbon, and the discharge capacity at the 20th cycle was 358 mAh / g of carbon.

Embodiment 18 Embodiment 18 is changed to Embodiment 18.

That is, expanded graphite and cupric oxide (particle size 23
μm) to 9: 1 (graphite / (graphite + copper oxide) =
A negative electrode was produced by the method described in Example 13 except that the negative electrode was set to 0.90). The produced negative electrode had a surface area of 8 cm ² and a thickness of 81 μm (the thickness of the current collector was 50 μm).

The negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 467 mAh / g of carbon, and the discharge capacity at the 20th cycle was 412 mAh / g of carbon.

Example 19 Example 13 was described in Example 13 except that the weight ratio of expanded graphite to cupric oxide (particle size 23 μm) was 6: 4 (graphite / (graphite + copper oxide) = 0.60). The negative electrode was produced by the method described above. The produced negative electrode had a surface area of 8 cm ² and a thickness of 89 μm (the thickness of the current collector was 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 433 mAh / g of carbon, and the discharge capacity at the 20th cycle was 407 mAh / g of carbon.

Example 20 Example 13 was described except that the weight ratio between expanded graphite and cupric oxide (particle size 23 μm) was 5: 5 (graphite / (graphite + copper oxide) = 0.50). The negative electrode was produced by the method described above. The produced negative electrode had a surface area of 8 cm ² and a thickness of 91 μm (the thickness of the current collector was 50 μm).

The negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 367 mAh / g of carbon, and the discharge capacity at the 20th cycle was 352 mAh / g of carbon.

Example 21 Example 13 was described in Example 13 except that the weight ratio between expanded graphite and cupric oxide (particle size: 23 μm) was 4: 6 (graphite / (graphite + copper oxide) = 0.40). The negative electrode was produced by the method described above. The produced negative electrode had a surface area of 8 cm ² and a thickness of 111 μm (the thickness of the current collector was 50 μm).

The negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 366 mAh / g of carbon, and the discharge capacity at the 20th cycle was 346 mAh / g of carbon.

Comparative Example 6 Expanded graphite only (weight ratio graphite / (graphite + copper oxide) = 1)
And a negative electrode was produced by the method described in Example 1.
The produced negative electrode had a surface area of 8 cm ² and a thickness of 107 μm.
(The thickness of the current collector is 50 μm).

The negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 352 mAh / g of carbon, and the discharge capacity at the 20th cycle was 349 mAh / g of carbon.

Comparative Example 7 Example 13 was described except that the weight ratio between expanded graphite and cupric oxide (particle size 23 μm) was 2: 8 (graphite / (graphite + copper oxide) = 0.20). The negative electrode was produced by the method described above. The produced negative electrode had a surface area of 8 cm ² and a thickness of 124 μm (the thickness of the current collector was 50 μm).

This negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 278 mAh / g of carbon, and the discharge capacity at the 20th cycle was 250 mAh / g of carbon.

Comparative Example 8 Example 13 was described except that the weight ratio between expanded graphite and cupric oxide (particle size: 23 μm) was 1: 9 (graphite / (graphite + copper oxide) = 0.10). The negative electrode was produced by the method described above. The produced negative electrode had a surface area of 8 cm ² and a thickness of 124 μm (the thickness of the current collector was 50 μm).

The negative electrode was evaluated by the method described in Example 1.

As a result, the discharge capacity at the second cycle was 237 mAh / g of carbon, and the discharge capacity at the 20th cycle was 225 mAh / g of carbon.

Table 3 shows the results of Examples 13 to 21 and Comparative Examples 6 to 8. Regarding these, the weight ratio of expanded graphite to the mixture of expanded graphite and copper oxide and graphite 1 in the second cycle
FIG. 1 shows the relationship of the discharge capacity per g. Accordingly, the weight ratio of graphite to copper oxide is preferably in the range of 9.8: 0.2 to 4: 6, and particularly preferably in the range of 9.8: 0.2 to 6: 4. It turned out.

[0119]

[Table 3]

Example 22 Preparation of Negative Electrode Natural graphite manufactured by Madagascar was used as a main negative electrode active material, and commercially available cupric oxide (particle diameter: 27 μm) was placed in a mortar at a weight ratio of 9.5: 0.5. Then, a nonionic dispersant is added, and polytetrafluoroethylene (the weight ratio of the mixture of graphite and cupric oxide after drying and polytetrafluoroethylene is 91: 9). The dispersion liquid was added to make a paste, and nickel 3
It was applied to a three-dimensional porous current collector, and the paste was applied to the inside of the hole. This was dried at 60 ° C., heat treated at 240 ° C., pressed, and further dried at 200 ° C. under reduced pressure to remove moisture, and used as a negative electrode. This negative electrode has a diameter of 14.5 m.
m, a pellet having an electrode thickness of 0.41 mm.

Preparation of Positive Electrode Lithium carbonate and cobalt carbonate, and antimony trioxide were mixed at a ratio of lithium atom to cobalt atom and antimony atom of 1:
Each was weighed so as to be 0.95: 0.05, mixed in a mortar, baked in air at 900 ° C. for 20 hours, and then ground in a mortar to obtain an active material powder. This active material had a composition of Li _0.98 Co _0.95 Sb _0.05 O ₂ . The positive electrode active material thus obtained was mixed with acetylene black, a nonionic dispersant was added, and polytetrafluoroethylene (after drying, the weight ratio of the positive electrode active material to acetylene black and polytetrafluoroethylene was , 100: 10: 5), and the mixture was made into a paste by applying the dispersion liquid to a titanium mesh current collector. This is dried at 60 ° C., 24
After heat treatment at 0 ° C, press, and 2 to remove moisture
What was dried under reduced pressure at 00 ° C. was used as a positive electrode. This positive electrode is a pellet having a diameter of 14.5 mm and an electrode thickness of 0.93 mm.

Assembling of Battery As shown in FIG. 2, the positive electrode current collector 2 was previously attached to the inner bottom surface by welding, and the positive electrode 3 was crimped to the positive electrode can 1 on which the insulating packing 8 was placed. Next, a microporous polypropylene separator 7 was placed on top of this, and 1 mol / l LiPF ₆ was added to a 2: 1: 3 mixed solvent of ethylene carbonate, propylene carbonate, and diethyl carbonate.
Is dissolved in the electrolytic solution. On the other hand, the negative electrode current collector 5 is welded to the inner surface of the negative electrode can 4, and the negative electrode 6 is pressed to the negative electrode current collector. Next, the negative electrode 6 is placed on the separator 7 and the positive electrode can 1 and the negative electrode can 4 are caulked with the insulating packing 8 interposed therebetween, thereby producing a coin-type battery.

Evaluation of Battery The produced coin-type battery was charged at a charging / discharging current of 2 mA and reached a charging upper limit voltage of 4.2 V, and after reaching 4.2 V, was charged at a constant voltage of 4.2 V. The charging time was 12 hours. did. The capacity was measured with the lower limit voltage of the discharge being 2.5 V. The evaluation was performed on the discharge capacity of the battery.

As a result, the average voltage in the discharge was 3.7
V, and the discharge capacity in the second cycle was 18 mAh, 1
The discharge capacity at the 0th cycle was 16 mAh.

Comparative Example 9 A negative electrode was produced by the method described in Example 22 using only natural graphite produced in Madagascar. The size and thickness of the produced negative electrode are the same. The positive electrode and the battery were also prepared in Example 22.
Was prepared by the method described in (1).

This battery was evaluated by the method described in Example 22.

As a result, the average voltage in the discharge was 3.7
V, and the discharge capacity in the second cycle was 14 mAh, 1
The discharge capacity at the 0th cycle was 13 mAh.

Example 23 Preparation of Negative Electrode Expanded graphite (flaky, particle size 8 μm,
d ₀₀₂ is 0.337 nm, Lc is 17.2 nm, La is 12.5 nm, R value is 0.1, and specific surface area is 9.5 m ² /
g) and a commercially available cupric oxide (particle size: 15 μm) sieved and mixed in a mortar at a weight ratio of 9: 1, a nonionic dispersant was added, and polytetrafluoroethylene (after drying) was added. The weight ratio of the combination of graphite, cupric oxide and polytetrafluoroethylene is 91: 9.)
Was added to a nickel three-dimensional porous current collector, and the paste was applied to the pores. This was dried at 60 ° C., heat treated at 240 ° C., pressed, and further dried at 200 ° C. under reduced pressure to remove moisture, and used as a negative electrode. This negative electrode is a pellet having a diameter of 14.5 mm and an electrode thickness of 0.38 mm.

Preparation of Positive Electrode Lithium carbonate and manganese dioxide were each weighed so that the ratio of lithium atoms to manganese atoms was 1.1: 2, mixed in a mortar, and then in air at 900 ° C. for 3 days. The active material LiM is fired and then crushed in a mortar.
A powder of n ₂ O ₄ was obtained. The positive electrode active material thus obtained is mixed with a conductive material (a mixture of acetylene black and expanded graphite at a weight ratio of 2: 1), a nonionic dispersant is added, and polytetrafluoroethylene (after drying, The weight ratio between the positive electrode active material and the conductive material, polytetrafluoroethylene,
100: 10: 5. The dispersion liquid was added to form a paste, and the paste was applied onto a titanium mesh current collector. This was dried at 60 ° C., heat-treated at 240 ° C., pressed, and dried at 200 ° C. under reduced pressure to remove moisture, and used as a positive electrode. This positive electrode has a diameter of 1
The pellets are 4.5 mm and the thickness of the electrodes is 1.0 mm.

Battery assembly Ethylene carbonate and γ-butyrolactone were used in the electrolyte.
1m in a 3: 1: 3 mixed solvent with diethyl carbonate
A coin-type battery was produced by the method described in Example 22 except that a solution of ol / l LiPF6 was used.

Evaluation of Battery The produced coin battery was charged at a charging / discharging current of 1 mA and reached a charging upper limit voltage of 4.2 V, and after reaching 4.2 V, was subjected to a constant voltage charging of 4.2 V, and the charging time was set to 24 hours. did. The capacity was measured with the lower limit voltage of the discharge being 2.5 V. The evaluation was performed on the discharge capacity of the battery.

As a result, the average voltage in the discharge was 3.7
V, and the discharge capacity in the second cycle was 15 mAh, 1
The discharge capacity at the 0th cycle was 13 mAh.

Comparative Example 10 Expanded graphite (flaky, particle size 8 μm, d ₀₀₂ 0.337 n
A negative electrode was produced by the method described in Example 23 using only m and Lc of 17.2 nm, La of 12.5 nm, R value of 0.1, and specific surface area of 9.5 m ² / g). The size and thickness of the produced negative electrode are the same. A positive electrode and a battery were also prepared by the method described in Example 23.

This battery was evaluated by the method described in Example 23.

As a result, the average voltage in the discharge was 3.7
V, and the discharge capacity in the second cycle was 13 mAh, 1
The discharge capacity at the 0th cycle was 11 mAh.

[0136]

[Table 4]

Table 4 shows the results of Examples 22 and 23 and Comparative Examples 9 and 10. Accordingly, when a negative electrode in which graphite and copper oxide are mixed is used, a high-capacity lithium secondary battery can be manufactured.

[0138]

The negative electrode according to the present invention, that is, an electrode obtained by mixing copper oxide and a binder with graphite capable of intercalating / deintercalating lithium exhibits a large discharge capacity. Further, it is possible to reduce the number of steps in manufacturing the electrode. Furthermore, a lithium secondary battery with a high battery voltage can be provided because it has a high capacity and can use a lower potential of the negative electrode. Therefore, an excellent lithium secondary battery can be provided using the negative electrode according to the present invention.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a weight ratio of expanded graphite to a mixture of expanded graphite and copper oxide and a discharge capacity per 1 g of graphite in a second cycle.

FIG. 2 shows Examples 22 and 23 of the present invention and Comparative Examples 9 and 10.
It is explanatory drawing of the battery manufactured in.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 positive electrode can 2 positive electrode current collector 3 positive electrode 4 negative electrode can 5 negative electrode current collector 6 negative electrode 7 separator 8 insulating packing

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Okamoto 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Kazuo Yamada 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (72) Inventor Tetsuya Yoneda 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-5-258773 (JP, A) JP-A-4-259764 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/02 H01M 4/36-4/62

Claims (3)

(57) [Claims] 1. A battery comprising a positive electrode, a negative electrode and a non-aqueous ion conductor, wherein the negative electrode has lithium ion indium.
Graphite that can be tarcalated and deintercalated
And copper oxide and a binder, and a mixture of the graphite and the copper oxide.
The weight ratio of the compound to the binder is 99: 1 to 70:30
Is a lithium secondary battery. 2. The method according to claim 1, wherein the positive electrode, the negative electrode and a non-aqueous ion conductor are used.
In the above battery, the negative electrode has lithium ion indium.
Graphite that can be tarcalated and deintercalated
And copper oxide and a binder, and the graphite and the copper oxide
Lithium secondary having a weight ratio of 9.8: 0.2 to 4: 6
battery. 3. The method according to claim 1, wherein the positive electrode, the negative electrode and a non-aqueous ion conductor are used.
In the above battery, the negative electrode has lithium ion indium.
Graphite that can be tarcalated and deintercalated
And copper oxide and a binder, and the graphite has a (002) plane.
Has an average surface spacing (d ₀₀₂ ) of 0.335 to 0.340 n
m, crystallite thickness (Lc) in the (002) plane direction is 10 nm
As described above, the crystallite thickness (La) in the (110) plane direction is 10 n
m or more.