JPH11307082A - Organic electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer electrolyte battery with large capacity density, by appropriately selecting an average grain size of nodular graphite used for a negative electrode and appropriately specifying the polymer contents in positive and negative mixes. SOLUTION: In an organic electrolyte battery equipped with a positive- electrode mix layer including a lithium-containing oxide and a polymer and borne by a current collector, a porous separator made of a polymer, a negative- electrode mix layer including a graphitic particle body and a polymer and borne by a current collector, and an organic electrolyte held by the positive- electrode mix layer, the negative-electrode mix layer, and the separator, modular graphite having an average grain size of 6 to 35 μm and made by carbonizing and then graphitizing a graphitic mesophase particle body, is used as the graphitic particle body. A discharge characteristic of a polymer electrolyte battery and those of batteries taken as comparison examples are shown in a figure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an organic electrolyte battery,
In particular, the present invention relates to an organic electrolyte secondary battery in which an electrode and a separator contain a polymer that absorbs and retains an organic electrolyte, and the electrode and the separator can be integrated by heat fusion.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as portable telephones and notebook computers, there is a strong demand for small, lightweight, and high energy density secondary batteries. To meet such demands, various secondary batteries have been developed. Lithium secondary batteries using lithium as the negative electrode active material
It is attracting attention because high energy density can be expected. Above all, a so-called polymer electrolyte secondary battery in which a positive electrode, a negative electrode, and a separator contain a polymer, and the polymer absorbs and holds an organic electrolyte, has attracted attention. This polymer electrolyte secondary battery uses a copolymer of vinylidene fluoride and propylene hexafluoride as a polymer, and has a positive electrode,
Since the separator and the negative electrode can be integrated by heat fusion, they have attracted attention as a battery system closest to the practical application of a thin battery (Japanese Patent Application Laid-Open No. 8-507407).

The above-mentioned polymer electrolyte secondary battery is manufactured, for example, as follows. First, a paste is prepared by adding an organic solvent solution of a polymer and di-n-butyl phthalate as a pore-forming agent to a mixture of an electrode active material powder such as lithium cobalt oxide or graphite particles and a conductive agent powder. After this paste is applied to a current collector, the paste is dried and the organic solvent is removed to obtain an electrode sheet. A separator sheet made of a polymer containing a pore-forming agent is interposed between the positive electrode sheet and the negative electrode sheet thus obtained, and are thermally fused and integrated by pressing under heating to obtain a battery element sheet. Next, the battery element sheet is immersed in an extraction solvent such as diethyl ether to extract and remove the pore-forming agent to impart porosity, and then impregnate the pores and the polymer itself with an organic electrolyte. As a negative electrode active material of a lithium secondary battery, various carbonaceous materials, such as graphite, coke, and carbon fiber, which reversibly intercalate / deintercalate lithium are known. Coke has already been studied as a negative electrode active material of this type of polymer electrolyte secondary battery. Spheroidal graphite particles obtained by carbonizing carbonaceous mesophase particles and then graphitizing are known to provide a negative electrode for a lithium battery having a high capacity and excellent cycle characteristics (Japanese Patent Application Laid-Open No. 5-290833). Thus, these spherical graphite particles are also considered promising.

[0004] The capacity density of the polymer electrolyte battery obtained as described above largely depends on the mixing ratio of the polymer in the electrode. That is, if the ratio of the polymer in the electrode is high, the amount of the active material is relatively reduced, and if the ratio of the polymer is low, the binding strength is inferior and the electrode strength is reduced. Therefore, after applying the electrode material paste to the current collector,
It is preferable to increase the packing density of the active material by rolling or the like. When the electrode is manufactured by such a method, if the mixing ratio of the polymer is increased, the electrode becomes rubbery and cannot be sufficiently rolled. Further, when a lath plate or the like is used as the current collector of the electrode, the current collector also extends together with rolling, and in severe cases, the current collector is torn off, so that the packing density of the active material cannot be increased. Also,
If the blending ratio of the polymer is small, the electrode and the separator cannot be heat-sealed together, leaving a gap between the electrode and the separator, increasing the internal resistance of the battery, and obtaining stable battery performance. Absent. Therefore, conventionally, it has been considered appropriate that the polymer content in the electrode mixture layer is about 20% by weight. In particular, the carbon material of the negative electrode active material changes its physical properties, particularly its surface area, depending on its type, particle size, and the like. Therefore, the amount of polymer required to form an electrode also changes, and the capacity density of the obtained electrode is affected.

[0005]

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a polymer electrolyte battery having a large capacity density by appropriately selecting an electrode, particularly an active material for a negative electrode. Another object of the present invention is to provide a polymer electrolyte battery having a higher capacity density by appropriately setting the polymer content in the electrode.

[0006]

An organic electrolyte battery according to the present invention comprises a positive electrode mixture supported by a current collector containing 5 to 10% by weight of a lithium-containing oxide as an active material and a polymer for absorbing and retaining an organic electrolyte. Layer, a porous separator made of a polymer that absorbs and retains the organic electrolyte, a graphite material of the active material, and 7 to 16% by weight of the polymer that absorbs and retains the organic electrolyte.
A negative electrode mixture layer supported by a current collector, and an organic electrolyte held by the positive electrode mixture layer, the negative electrode mixture layer and the separator, wherein the graphitic granules are made of carbonaceous mesophase granules. And then graphitized average particle size 6-35μ
m is a spheroidal graphite. The graphite grains have a lattice spacing of 3.365 to 3.3 in X-ray diffraction.
90 Å, crystallite size in c-axis direction is 2
00-650 Å, the ratio I ₁₃₆₀ / I of the peak intensity I ₁₃₆₀ of 1360 cm ^-1 to the peak intensity I ₁₅₈₀ of 1580 cm ^-1 in the argon laser Raman spectroscopy
Preferably, ₁₅₈₀ is in the range of 0.20 to 0.40. Further, the polymer is a copolymer of vinylidene fluoride and propylene hexafluoride, the polymer content in the negative electrode mixture layer is 7 to 16% by weight, and the active material in the positive electrode mixture layer is lithium cobalt oxide. Yes and has a polymer content of 5
It is preferably from 10 to 10% by weight. The calculation of the polymer content does not include the electrolytic solution.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have applied a high-capacity and excellent cycle characteristic spheroidal graphite to a negative electrode active material together with a preferable content of a polymer in an electrode mixture of a polymer electrolyte battery. As a result of searching for conditions under which the packing density is high and stable performance can be exhibited, it has been found that an excellent battery can be obtained by using spherical graphite particles having an average particle diameter of 6 to 35 μm as described above. That is, the spherical graphite particles obtained by carbonizing and graphitizing the carbonaceous mesophase particles have a large lithium storage capacity as compared with petroleum coke or the like, and can improve the discharge capacity when used as an electrode. Regarding the particle size of the spherical graphite particles, those having a large particle size have a small surface area, so that if the polymer content is the same, the spherical graphite particles having a small particle size are used for the binding property between the spherical graphite particles by the polymer. Bigger than things. For this reason, a small amount of the polymer can provide the binding property between the graphite particles, so that the discharge capacity is increased. However, when the particle size increases, when the electrode mixture paste is applied to a current collector such as a lath metal to manufacture an electrode, uneven coating of the surface of the electrode plate can be uneven, and the manufacturing efficiency only deteriorates. In addition, since the particles easily fall off, the cycle characteristics deteriorate.

On the other hand, if the particle size of the spherical graphite particles is too small, the bulk becomes large and the total surface area of the powder becomes large. For this reason, if an electrode having the same polymer content as when a large particle size electrode is used is produced, the binding of the spherical graphite particles to each other by the polymer becomes insufficient, and the electrical contact between the powders becomes unstable, resulting in a poor electrical conductivity. Worse. Therefore, the polymer content must be increased in order to obtain a sufficient binding property, so that the amount of spheroidal graphite is relatively reduced, the packing density is reduced, and the discharge capacity is reduced. When the binding property is insufficient, the electrode mixture layer and the current collector are not sufficiently adhered to each other, resulting in an electrode plate having low tensile strength. Further, there is a disadvantage that the electrode mixture layer absorbs the electrolyte too much and bulges greatly. Furthermore, spherical graphite particles having a small particle size and a large surface area have a problem in handling safety in an atmosphere containing oxygen.
From the above viewpoints, the average particle size of the spheroidal graphite is selected. The polymer content in the electrode mixture layer was 7 in the negative electrode.
In the positive electrode, when lithium cobaltate is used as the active material, the content is preferably 5 to 10% by weight.

The electrode of the polymer electrolyte battery according to the present invention is preferably prepared as follows. First,
Electrode active materials such as lithium cobalt oxide and spherical graphite particles,
A paste is prepared by mixing a conductive agent, a solution of a polymer in an organic solvent and a pore-forming agent. After this paste is applied to a current collector and dried, it is rolled with a pressure roller and cut into predetermined dimensions to obtain an electrode sheet. The separator is prepared in a state of a polymer sheet mixed with a pore-forming agent. Then, in the state of the sheet thus obtained, or in a state where the positive electrode, the negative electrode and the separator are integrally heat-fused and assembled into a battery element, the polymer is extracted by extracting the pore-forming agent with a solvent such as diethyl ether. The portion is made porous to form pores that allow the electrolyte to permeate.

The polymer used for the electrode and the separator of the present invention is preferably a copolymer of vinylidene fluoride and propylene hexafluoride, and the pore-forming agent is preferably di-n-butyl phthalate. It is not something to be done. As the positive electrode active material, LiCoO ₂ , LiNiO ₂ ,
An oxide such as LiMn ₂ O ₄ capable of reversibly injecting and extracting lithium by charge and discharge is used. Above all, LiCoO ₂
Is preferably used.

The current collector of the positive electrode may be a foil of aluminum, titanium, stainless steel or the like, a perforated plate, a lath plate, a net, or the like. The current collector of the negative electrode may be a foil or hole of copper, stainless steel, or the like. A perforated plate, a lath plate, a net, and the like are used. When a configuration in which cells are stacked in multiple layers is used, it is preferable to use a perforated plate such as a perforated plate. Organic electrolytes include:
LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃
Such a combination of a solute and an organic solvent such as ethylene carbonate, propylene carbonate, and dimethoxyethane is appropriately selected from those known as those used for organic electrolyte batteries.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. << Example 1 >> Copolymer of vinylidene fluoride and propylene hexafluoride (proportion of propylene hexafluoride: 12% by weight)
(Hereinafter, represented by P (VDF-HFP)) 100 g was dissolved in 500 g of acetone, and di-n-phthalic acid was added to the solution.
-Butyl (hereinafter, referred to as DBP) 150 g was added to obtain a mixed solution. After applying this solution on a glass plate,
The acetone was removed by drying to obtain a polymer sheet having a thickness of 50 μm. Cut this sheet, size 35mm x 6
The separator sheet was 5 mm. On the other hand, P (VDF-
A paste prepared by mixing 900 g of HFP) in 1500 g of acetone, 900 g of lithium cobaltate LiCoO ₂ , 50 g of acetylene black, and 135 g of DBP. This paste was applied to one side of an aluminum lath plate of a current collector, dried, and then rolled by a roll press. Thus, a sheet having a thickness of 100 μm was obtained. This sheet was cut into a positive electrode sheet having a size of 30 mm × 60 mm.

In a solution of 120 g of P (VDF-HFP) dissolved in 1000 g of acetone, 750 g of spherical graphite particles (manufactured by Osaka Gas) having an average particle size of 25 μm obtained by carbonizing and graphitizing carbonaceous mesophase granules, The paste was obtained by mixing 60 g of graphite fiber (manufactured by Osaka Gas) and 180 g of DBP. The graphite fibers used here are obtained by graphitizing carbon fibers obtained by a vapor growth method. This paste was applied to both sides of a copper lath plate of a current collector, dried, and then rolled by a roll press. Thus thickness 300
A μm sheet was obtained. Cut this sheet, size 30
A negative electrode sheet of mm × 60 mm was obtained. The current collectors of the positive electrode and the negative electrode used had a conductive carbon film formed on the surface in advance. This conductive carbon film is formed by applying a dispersion of acetylene black in an N-methylpyrrolidone solution of polyvinylidene fluoride (concentration: 12% by weight) to a thickness of 60 μm on the surface of the current collector and then applying a temperature of 80 ° C. or higher. And dried.

A positive electrode sheet is disposed on both sides of the negative electrode sheet obtained as described above via a polymer sheet as a separator, and pressure is applied between two pressure rollers heated to 120 ° C. To obtain a battery element. This battery element was then immersed in diethyl ether as an extraction solvent to extract and remove DBP, and then dried in vacuum at 50 ° C. By removing DBP, fine pores are formed in the polymer portion, and the polymer becomes porous. Then, the electrode and the separator were immersed in the electrolyte to impregnate and hold the electrolyte in the pores in the separator. For the electrolyte, lithium hexafluorophosphate LiPF was mixed with a mixed solvent of ethylene carbonate and methyl ethyl carbonate at a volume ratio of 1: 3.
₆ was dissolved at a rate of 1 mol / l. The battery element thus prepared was packaged with a laminate film having an aluminum film disposed between insulating resin films to obtain a battery having a thickness of 0.6 mm and a size of 35 mm × 60 mm. The polymer content (not including the electrolytic solution) in the positive electrode mixture layer of this battery was 8.7% by weight, and that of the negative electrode was 12.
It was 9% by weight.

Example 2 A battery was manufactured in the same manner as in Example 1 except that the average particle size of the spherical graphite of the negative electrode was about 4, 6, 10, 35, or 40 μm. The average particle size is about 40.
When an electrode was manufactured using spherical graphite particles of μm, uneven coating due to unevenness on the electrode surface was large, and it was difficult to manufacture a battery integrally with the separator.

Comparative Example 1 Example 1 except that petroleum coke powder having an average particle size of about 10 μm was used instead of the spherical graphite particles.
In the same manner as in the above, a battery was produced.

The batteries of the above Examples and Comparative Examples were discharged at a discharge rate of 0.2 C to a final voltage of 3.0 V. FIG. 1 shows the discharge curves of these batteries. In FIG. 1, each battery is distinguished by the particle size of the spherical graphite or coke used for the negative electrode. The discharge capacity is expressed as 100% of that of a battery using spherical graphite having an average particle size of 10 μm. As is evident from FIG. 1, the battery of the example using the spherical graphite particles obtained by carbonizing and graphitizing the carbonaceous mesophase granules was compared with the battery of the comparative example using petroleum coke for the negative electrode. In each case, the discharge capacity is large. In particular, the discharge capacity is larger when the diameter of the spherical graphite particles is larger. If the particle size of the spheroidal graphite is too small, the bulk increases and the total surface area of the particles increases. For this reason, if an electrode is produced with the same polymer content in the mixture as that using graphite particles having a large particle size, the binding of the spherical graphite particles to each other by the polymer becomes insufficient, so that the electrical connection between the particles is not sufficient. The electrical contact becomes unstable and the conductivity deteriorates. In order to obtain sufficient binding between the particles, the amount of the polymer in the mixture must be increased, whereby the packing density of the spheroidal graphite decreases relatively, and the discharge capacity as an electrode decreases. As shown in FIG. 1, in the case of spherical graphite, a preferable discharge capacity is obtained when the average particle size is in the range of 6 to 35 μm. On the other hand, those having a large particle diameter have a small surface area, so that the binding property by the polymer is sufficient. However, when the particle size is large, unevenness of coating is likely to be formed on the surface of the electrode plate when the electrode is manufactured, and the particles also easily fall off, resulting in poor cycle characteristics.

Example 3 The negative electrode and the separator sheet were the same as in Example 1, and the polymer P (V
DF-HFP) was changed to 0, 2, 5, 7, 10, 15 or 25% by weight to produce a battery in the same manner. However, the amount of lithium cobalt oxide as the positive electrode active material and the amount of acetylene black as the conductive agent were the same as in Example 1, and the amount of DBP was a constant (1.5) with respect to P (VDF-HFP). These are called Group A batteries.

Example 4 The positive electrode and the separator sheet were the same as in Example 1, and the polymer P (V
DF-HFP) content of 0, 5, 7, 10, 12, 1
A battery was prepared in the same manner except that the battery was replaced with 5, 16 or 25% by weight. However, the amounts of the spherical graphite as the negative electrode active material and the graphite fibers as the conductive agent were the same as in Example 1, and the amount of DBP was P (VDF-
HFP) was constant (1.5). These are called group B batteries.

The internal resistances of the above-mentioned A group batteries and B group batteries were measured by an AC impedance method of 1 KHz.
The results are shown in FIGS. 2 and 3, respectively. As is clear from these figures, based on the internal resistance of the battery,
It can be seen that the optimum polymer content in the electrode mixture layer is much lower than the conventional 20% by weight. That is, the minimum value of the internal resistance is 5 to 10% by weight for the positive electrode,
The negative electrode has a polymer content of 7 to 16% by weight. Where the blending ratio of the polymer having no conductivity per se is high, the internal resistance of the battery increases, and where the blending ratio of the polymer is low, the contact between the active materials in the electrodes becomes poor. On the other hand, if the polymer content is small, the electrode and the separator cannot be sufficiently thermally fused, so that a gap is formed between the electrode and the separator. For this reason, the internal resistance increases,
Stable battery performance cannot be obtained, and in severe cases, discharge may not be possible.

[0021]

As described above, according to the present invention, a polymer having a large capacity density can be obtained by appropriately selecting the average particle size of the spherical graphite used for the negative electrode and appropriately specifying the polymer content in the positive / negative electrode mixture. An electrolyte battery can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing discharge characteristics of a polymer electrolyte battery according to an example of the present invention and a battery of a comparative example.

FIG. 2 is a diagram showing the relationship between the polymer content of the positive electrode and the internal resistance of the battery.

FIG. 3 is a diagram showing the relationship between the polymer content of a negative electrode and the internal resistance of a battery.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobuo Eda 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A positive electrode mixture layer containing 5 to 10% by weight of a lithium-containing oxide as an active material and a polymer that absorbs and retains an organic electrolyte, and is supported by a current collector, and includes a polymer that absorbs and retains an organic electrolyte. The porous separator, the polymer that absorbs and retains the graphite material of the active material and the organic electrolyte are 7 to
A negative electrode mixture layer containing 16% by weight and supported by a current collector; and an organic electrolyte absorbed and held by the positive electrode mixture layer, the negative electrode mixture layer, and the separator, wherein the graphitic particles are formed of carbonaceous mesophase. An organic electrolyte battery comprising spherical graphite having an average particle diameter of 6 to 35 μm obtained by carbonizing granules and then graphitizing. 2. The graphitic granules have a lattice spacing in X-ray diffraction of 3.365 to 3.390 angstroms,
The crystallite size in the c-axis direction is 200 to 650 Å, and 1580 in argon laser Raman spectroscopy.
The ratio I _{1360 /} I ₁₅₈₀ of the peak intensity I ₁₃₆₀ at ₁₃₆₀ cm ^{−1 to} the peak intensity I _{1580 at} cm ⁻¹ is 0.20 to 0.4.
The organic electrolyte battery according to claim 1, which is in a range of 0. 3. The polymer according to claim 1, wherein the polymer is a copolymer of vinylidene fluoride and propylene hexafluoride, the polymer content in the negative electrode mixture layer is 7 to 16% by weight, and the active material in the positive electrode mixture layer is cobalt. 3. The organic electrolyte battery according to claim 2, wherein the battery is lithium oxide and has a polymer content of 5 to 10% by weight.