JPH11288718A - Non-aqueous solvent secondary battery - Google Patents

Abstract

(57) [Problem] To provide a non-aqueous solvent secondary battery having a large discharge capacity and good cycle characteristics. The negative electrode active material is graphitized mesophase microspheres, and the negative electrode binder is 0.5% by weight or more and 1% by weight or less of the whole negative electrode constituent material and 0.5% by weight of the whole negative electrode constituent material. A composite binder with not less than 2% by weight and not more than 2% by weight of a synthetic rubber latex type adhesive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous solvent secondary battery using a carbon material as a negative electrode active material and a lithium-containing metal oxide as a positive electrode active material, and has a large discharge capacity and good cycle characteristics. A non-aqueous solvent secondary battery.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as cellular phones have rapidly become smaller and cordless, the development and spread of electric vehicles has been desired in the field of automobiles due to environmental problems and energy problems. In addition, a battery serving as a power supply source is required to have a high energy density. As batteries used in these devices, secondary batteries such as nickel cadmium batteries, nickel hydrogen batteries, and lead-acid batteries have been well known. However, these secondary batteries are heavy and have an unsatisfactory energy density.

[0003] Therefore, a fired body of organic compound, coke,
A non-aqueous solvent secondary battery (so-called lithium ion secondary battery) using a carbon material such as graphite as a negative electrode and a lithium-containing metal oxide as a positive electrode has been developed, and has already been put to practical use in the field of electronic devices. . In the mechanism of this lithium ion secondary battery, lithium in the positive electrode becomes ions as a result of charging and elutes into the electrolytic solution, lithium ions in the electrolytic solution are occluded in the carbon of the negative electrode, and the opposite reaction proceeds during discharging. That is. This battery is expected to be used not only as an electronic device but also as a battery for an electric vehicle because of its light weight and high energy density.

As a prior art relating to this lithium ion secondary battery, a non-aqueous solvent using a fired body of an organic compound (eg, novolak resin) as a negative electrode active material and a composite binder of carboxymethyl cellulose and styrene butadiene rubber as a negative electrode binder is used. Secondary battery (JP-A-4-342966)
Or a non-aqueous solvent secondary battery using polyvinylidene fluoride as a negative electrode binder (Industrial Material Vol. 44 No. 13
78 [1996]).

[0005]

The carbon material obtained by calcining an organic compound has a low crystallinity and contains a large amount of impurities such as hydrogen and oxygen. The secondary battery had a small discharge dose.
For the negative electrode binder, in the case of the prior art in which a composite binder of carboxymethylcellulose and styrene-butadiene rubber was used as the negative electrode binder, the optimum amount of carboxymethylcellulose was 1 to 1.5 of the entire negative electrode constituent material.
%, The optimum amount of styrene-butadiene rubber is set to 2 to 3% by weight of the whole negative electrode constituent material, the amount of the binder is relatively large, the resistance is increased, and the capacity and cycle characteristics are reduced. there were. Further, the conventional technique using polyvinylidene fluoride as a binder has a similar problem.

[0006]

Means for Solving the Problems In the non-aqueous solvent secondary battery, the present inventors have used graphitized mesophase spheres, which are carbon materials that are crystallized into a negative electrode active material and have few impurities, and a negative electrode binder. The present invention has been completed by reducing the amount. That is, the present invention provides a non-aqueous solvent secondary battery in which graphitized mesophase microspheres are used as a negative electrode active material, and 0.5% to 1% by weight of a cellulose ether-based material and 0.5% by weight or less of the whole negative electrode constituent material. 0.
It is characterized by comprising a negative electrode using 5% by weight or more and 2% by weight or less of a synthetic rubber-based latex adhesive as a binder, a separator, and a positive electrode using a lithium-containing metal oxide as a positive electrode active material.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The non-aqueous solvent secondary battery of the present invention uses graphitized mesophase microspheres as a negative electrode active material. Graphitized mesophase small spheres are spherical particles obtained by melting pitches at a temperature of about 400 ° C. This graphite utilizes the phenomenon that lithium ions are absorbed in the lattice of graphite crystals.
The spacing between lattice (002) planes by X-ray diffraction is 3.45.
It is preferable that the size of the crystallite in the C-axis direction is 300 ° or more.

The non-aqueous solvent secondary battery uses a composite binder of a cellulose ether-based material and a synthetic rubber-based latex adhesive as a negative electrode binder. The role of the negative electrode binder is to bind the negative electrode active material firmly, maintain good cycle characteristics without deteriorating the discharge capacity even with repeated charge and discharge, and keep the electric resistance low, and achieve a sufficient discharge capacity Is to secure. The composite binder comprising the cellulose ether-based material and the synthetic rubber-based latex adhesive satisfies the above-mentioned properties required for the binder.

Further, the amount of the binder has a great influence on the discharge capacity and cycle characteristics of the battery. When the total amount of the negative electrode constituent material (the total amount of the active material and the binder) is 100% by weight and the amount of the binder is less than 1% by weight, the ability to bind the graphitized mesophase microspheres is reduced. As a result, the cycle characteristics deteriorate. On the other hand, the amount of the binder is 3% by weight.
If it exceeds, the electric resistance increases and the discharge capacity and the cycle characteristics deteriorate. Therefore, in the present non-aqueous solvent secondary battery, the amount of the binder is also limited, and the content of the cellulose ether-based material is 0.5% by weight or more and 1% by weight or less of the whole negative electrode constituting material, and the synthetic rubber-based latex type adhesive is used. Was set to 0.5% by weight or more and 2% by weight or less of the whole negative electrode constituting material.

[0010] The cellulose ether-based material includes
Any one or more of cellulose ethers and salts thereof may be used. As the cellulose ether, for example,
It is preferable to use one or more selected from the group of methylcellulose, ethylcellulose, benzylcellulose, triethylcellulose, cyanoethylcellulose, carboxymethylcellulose, carboxyethylcellulose, aminoethylcellulose, and oxyethylcellulose.
~ 2.5, average degree of polymerization 100 ~ 2000, average molecular weight 2
Those having 5,000 to 400,000 are preferred. Considering that these materials are relatively inexpensive, it is preferable to use sodium carboxymethylcellulose.

The synthetic rubber-based latex type adhesive preferably uses at least one of styrene butadiene rubber latex, nitrile butadiene rubber latex, methyl methacrylate butadiene rubber latex, chloroprene rubber latex, and carboxy-modified styrene butadiene rubber latex. . Above all, it is more preferable to use carboxy-modified styrene-butadiene rubber latex in consideration of the adhesion to the current collector.

The negative electrode is prepared by sufficiently mixing the graphitized mesophase microspheres with a predetermined amount of the aqueous cellulose-based material solution and a predetermined amount of the synthetic rubber-based latex adhesive solution to form a paste-like negative electrode mixture. After being applied to the current collector by a machine, it is dried and molded. Then, after drying, the graphitized mesophase small spheres as the active material and 0.5% by weight or more and 1% by weight or less when the entire negative electrode constituting material (the total amount of the active material and the binder) is 100% by weight. A negative electrode comprising a cellulose ether-based material and 0.5% by weight or more and 2% by weight or less of a synthetic rubber-based latex-type adhesive is obtained.

The positive electrode of the non-aqueous solvent secondary battery of the present invention uses a lithium-containing metal oxide as an active material, and if necessary, adds a conductive agent and a binder to form a positive electrode mixture. Similarly, it is applied to a current collector, dried and molded. The lithium metal-containing oxide used as the positive electrode active material is not particularly limited, and may be one used as an active material of a normal non-aqueous solvent secondary battery, for example, Li _x Mn ₂ O ₄ (x: 1.0 to 2). .
0), LiCoO ₂ , LiNiO _{2 and the} like can be used.

As the conductive agent, a carbon-based material such as carbon black, acetylene black, and graphite can be used. The mixing ratio varies depending on the conductivity of the active material and the shape of the electrode. It may be added up to 50% by weight. Further, the binder may be any as long as it is insoluble in the electrolytic solution, and a polytetrafluoroethylene, polyvinylidene fluoride, a fluorine-containing resin such as fluororubber, a polypropylene, a thermoplastic resin such as polyethylene can be used, The mixing ratio is preferably 20% by weight or less.

The separator separates the positive electrode and the negative electrode and holds the electrolyte, and a microporous film of polyethylene, polypropylene or the like can be used. In addition, an aprotic organic solvent can be used as a solvent constituting the electrolytic solution of the present non-aqueous solvent secondary battery. For example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone,
Acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolan, methylene chloride and the like;
Mixtures of more than one species can also be used.

As the electrolyte to be dissolved, LiI, Li
ClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF _{6 and the} like can be used. The electrolyte and the solvent are mixed in a sufficiently dehydrated state to form an electrolyte. The concentration of the electrolyte in the electrolyte is at least 0.1 mol / l in order to reduce the internal resistance due to the electrolyte. It is preferable to set it as above, and it is usually preferable to set it as 0.2 to 1.5 mol / l.

[0017]

EXAMPLES Hereinafter, non-aqueous solvent secondary batteries which are examples of the present invention will be described in detail, and comparative examples will be shown.
The difference between the comparative example and the example will be clarified. <Example> In this example, graphitized mesophase microspheres (MCMB-6-2 manufactured by Osaka Gas Chemicals) were used as the negative electrode active material.
8, average particle size of 6 μm), and sodium carboxymethylcellulose (hereinafter referred to as CMCNa) and carboxy-modified styrene-butadiene type latex (hereinafter simply referred to as SBR) were used as the negative electrode binder. With respect to 290 to 300 parts by weight of the graphitized mesophase microspheres, C
MCNa aqueous solution (weight fraction: 4%) 40 to 80 parts by weight,
3-12 parts by weight of SBR (weight fraction: 48.5%), water 6
0 to 70 parts by weight was sufficiently mixed with a kneader to obtain a paste-like negative electrode mixture.

This negative electrode mixture was applied to both sides of a copper foil having a width of 150 mm and a thickness of 10 μm as a current collector of the negative electrode using a coating machine (coater). After drying for minutes, a negative electrode having a thickness of 70 to 100 μm was obtained on both surfaces of the current collector. The negative electrode thus obtained is
CMCNa is contained in an amount of 0.5 to 1% by weight of the entire negative electrode constituent material,
BR contains 0.5 to 2% by weight of the whole negative electrode constituting material.

In this embodiment, as the positive electrode active material,
Li _1.03 Mn _1.97 O ₄ was used. This Li _1.03 Mn _1.97
370 parts by weight of O ₄ and carbon black 3 as a conductive agent
And 0 parts by weight are sufficiently mixed with 80 parts by weight of a solution obtained by dissolving 12 parts by weight of polyvinylidene fluoride powder as a binder in 88 parts by weight of N-methylpyrrolidone as a dispersant, thereby obtaining a paste-like positive electrode mixture. I got This positive electrode mixture was coated with a coating machine having a width of 15
It was applied to both sides of an aluminum foil having a thickness of 0 mm and a thickness of 20 μm and dried to obtain a positive electrode having a thickness of 90 μm on both sides of the current collector.

The positive electrode and the negative electrode obtained as described above were used. The positive electrode was 45 mm × 45 mm, and the negative electrode was 47 mm × 4 mm.
The positive electrode body and the negative electrode body were cut out to 7 mm, respectively.
The positive electrode body and the negative electrode body were laminated and arranged via a polyethylene separator (manufactured by Tonen Chemical Co., Ltd., thickness 25 μmm, width 58 mm) to form a test cell of a non-aqueous solvent secondary battery. FIG. 1 shows a schematic diagram of the test cell. The electrolytic solution used in this test cell was a mixed solution of ethylene carbonate and diethyl carbonate (volume ratio: 1: 1), L
iPF ₆ was dissolved at a rate of 1 mol / l, and the amount of liquid injected into the test cell was 20 cc.

A charging / discharging device was connected to the non-aqueous solvent secondary battery according to the embodiment of the present invention,
An experiment was conducted in which the battery voltage was in the range of 4.2 V to 3.0 V under a constant current of 10 V / cm ² and charge / discharge was repeated for a rest time of 10 minutes, and the maximum value of the discharge capacity per 1 g of the positive electrode active material of this example was obtained. And the value of the discharge capacity after 100 cycles was measured.
Then, the capacity deterioration rate was obtained by calculation using Equation 1. Table 1 shows the results.

[0022]

(Equation 1)

[0023]

[Table 1] Comparative Example 1 The non-aqueous solvent secondary battery of this comparative example is different from the non-aqueous solvent secondary battery of the above embodiment in the amount of the negative electrode binder. In Examples, the amount of the negative electrode binder was 1 to 3% by weight (CMCNa: 0.5 to 1% by weight, S
BR: 0.5 to 2% by weight), whereas in this comparative example, the amount of the negative electrode binder was 0.8% by weight of the whole negative electrode constituent material.
(CMCNa: 0.4% by weight, SBR: 0.4% by weight)
And the amount of the negative electrode binder is 3.5 to 4.5% by weight (CMCNa: 1 to 1.5% by weight, SBR: 2.5 to 3% by weight) of the whole negative electrode constituting material. . A test cell was constructed in the same manner as in the example, and the maximum value of the discharge capacity per 1 g of the positive electrode active material and the value of the discharge capacity after 100 cycles were measured to determine the capacity deterioration rate. Table 2 shows the results.

By comparing the data in Table 1 with the data in Table 2, the effect of the amount of the negative electrode binder on the cycle characteristics becomes clear. Although the maximum value of the discharge capacity is almost the same in both the example and the comparative example, the amount of the negative electrode binder of the comparative example is 0.8% by weight (CMCNa: 0.4% by weight). , SBR: 0.4% by weight) and 3.5 to 3.5% by weight.
4.5% by weight (CMCNa: 1 to 1.5% by weight, SB
R: 2.5 to 3% by weight), the discharge capacity after 100 cycles is less than 80 mAh, and the capacity deterioration rate is a value exceeding 0.2% cycle ^-1 .

As a result, the amount of the negative electrode binder is set to 1 to 3% by weight (CMCNa: 0.5 to 1% by weight, SBR: 0.5 to 2% by weight) of the whole negative electrode constituting material. It can be seen that the water solvent secondary battery has excellent cycle characteristics.

[0026]

[Table 2] Comparative Example 2 The non-aqueous solvent secondary battery of this comparative example is a conventional non-aqueous solvent secondary battery using an organic compound fired body as a negative electrode active material. 95 novolak resin in nitrogen atmosphere
After baking at 0 ° C., it was heat-treated at 2000 ° C. to carbonize it and pulverized into a powder having an average particle size of 6 μm. This powder was used as a negative electrode active material, and a negative electrode binder was 3.5 to 4.5% by weight (CMCNa: 1 to 1.5% by weight, SBR: 2.5 to 3% by weight) of the whole negative electrode constituent material. In the same process as in the example, a negative electrode body was prepared, a test cell was constructed in the same manner as in the example, and the maximum value of the discharge capacity per 1 g of the positive electrode active material and the value of the discharge capacity after 100 cycles were measured. The deterioration rate was determined. Table 3 shows the results.

When comparing the example with the comparative example based on the data in Tables 1 and 3, there is a difference in the maximum value of the discharge capacity, and the non-aqueous solvent secondary battery of the example is more excellent in this point. It has become something. This can be considered to be due to the difference in the negative electrode active material, and indicates that the graphitized mesophase microspheres are superior to the fired body of the organic compound as the negative electrode active material.

Also, the cycle characteristics of this comparative example show a peak when the amount of the negative electrode binder is 4% by weight (CMCNa: 1.5% by weight, SBR: 2.5% by weight).
Comparing the whole, this comparative example has a larger capacity deterioration rate than the embodiment. Further, the discharge capacity after 100 cycles is a value lower than that of the example by 9 mAh or more. Comprehensively evaluating these points, it can be said that the non-aqueous solvent secondary batteries of the above examples have better cycle characteristics.

[0029]

[Table 3] <Comparative Example 3> A nonaqueous solvent secondary battery of this comparative example uses a conventional negative electrode binder made of polyvinylidene fluoride (hereinafter referred to as PVD).
F)). That is, CMC which is the negative electrode binder of the non-aqueous solvent secondary battery of the above embodiment is used.
In this example, Na and SBR were changed to PVDF. A test cell was constructed in the same manner as in the example, and the maximum value of the discharge capacity per 1 g of the positive electrode active material and the value of the discharge capacity after 100 cycles were measured to determine the capacity deterioration rate. Table 4 shows the results. In this comparative example, when the amount of PVDF was set to 4% by weight or less of the whole negative electrode constituent material, the adhesion to the copper current collector was remarkably reduced, and the negative electrode could not be formed. And

As can be seen by comparing Tables 1 and 4, the amount of the negative electrode binder was 1 to 3% by weight (CMCN) of the whole negative electrode constituent material.
a: 0.5 to 1% by weight, SBR: 0.5 to 2% by weight), the non-aqueous solvent secondary battery of the example using the composite binder has both a discharge capacity and a capacity deterioration rate after 100 cycles. It shows good values, indicating that the cycle characteristics are excellent.

[0031]

[Table 4]

[0032]

The non-aqueous solvent secondary battery of the present invention has a larger discharge than a non-aqueous solvent secondary battery in which the negative electrode active material is a sintered body of an organic compound by using the graphitized mesophase microspheres as the negative electrode active material. You can get the capacity. In addition, the non-aqueous solvent secondary battery uses a composite binder of a cellulose ether-based material and a synthetic rubber-based latex-type adhesive as a negative electrode binder to form a non-aqueous solvent using polyvinylidene fluoride as a negative electrode binder. The amount of the binder can be reduced as compared with the secondary battery, and the battery has excellent cycle characteristics.

The use of a composite binder of a cellulose ether-based material and a synthetic rubber-based latex type adhesive as a negative electrode binder is adopted in a nonaqueous solvent secondary battery using a fired organic compound as a negative electrode active material. However, in this non-aqueous solvent secondary battery, the cellulose ether-based material is added in an amount of 0.5% by weight or more and 1% by weight or less of the whole negative electrode constituting material, and the synthetic rubber-based latex adhesive and 0% of the whole negative electrode constituting material are used. .
By setting the content to 5% by weight or more and 2% by weight or less, the amount of the binder is adjusted to a range smaller than the conventional range, and good cycle characteristics can be obtained.

The non-aqueous solvent secondary battery of the present invention having the above advantages not only contributes to further miniaturization of electronic equipment, but also can be used as a lighter and higher energy density battery for electric vehicles. .

[Brief description of the drawings]

FIG. 1 is a schematic view of a test cell of a non-aqueous solvent secondary battery according to an embodiment of the present invention.

Claims (1)

[Claims] 1. A graphitized mesophase microsphere is used as a negative electrode active material, and 0.5% by weight or more and 1% by weight or less of a cellulose ether-based material and 0.5% by weight or more and 2% by weight of the whole negative electrode constituting material. A non-aqueous solvent secondary battery comprising: a negative electrode using a synthetic rubber-based latex-type adhesive of not more than 5% by weight as a binder; a separator; and a positive electrode using a lithium-containing metal oxide as a positive electrode active material.