JPH09306502A - Electrode mix for nonaqueous battery, and nonaqueous battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode mix for a nonaqueous battery positive electrode preventing the formation of gel and stable by adding an organic acid to a mix comprising an electrode active material, an auxiliary conductive material, a fluorovinylidene polymer, and an organic solvent. SOLUTION: 9 pts.wt. LiNi0.8 Co0.2 O2 serving as an active material, 0.7 pts.wt. conductive carbon black, 0.3 pts.wt. fluorovinylidine polymer, and 6 pts.wt. N-methyl-2-pyrrolidone to which 0.1wt.% maleic acid is added are mixed to prepare mix slurry for a positive electrode 1. The mix slurry is applied to the one side of a copper foil and dried to obtain an electrode structure having a smooth positive electrode layer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a mixture (for coating) suitable for forming a positive electrode of a non-aqueous battery, particularly a lithium ion battery, and a non-aqueous battery having the formed positive electrode.

[0002]

2. Description of the Related Art In recent years, the development of electronic technology has been remarkable, and various devices have been reduced in size and weight. Along with the miniaturization and weight reduction of this electronic device, the demand for the miniaturization and weight reduction of a battery serving as a power source for the electronic device has also become very large. In order to obtain more energy with a small volume and weight, a high voltage per battery is required. From this viewpoint, a carbonaceous material capable of occluding lithium or lithium ions has recently been used as a negative electrode active material and a positive electrode active material. As a battery, for example, a battery using a non-aqueous electrolyte solution using a lithium-based composite metal oxide is drawing attention.

In the electrodes (positive electrode and negative electrode) of such a non-aqueous battery, for example, a binder (binder) is mixed with a powdery electrode forming material such as an electrode active material and a conductive auxiliary agent added as necessary. Then, the electrode mixture slurry obtained by dissolving or dispersing in a suitable solvent is applied on the current collector to form a mixture layer. The binder is
For example, it is necessary to exhibit durability to a non-aqueous electrolytic solution obtained by dissolving an electrolyte such as LiPF ₆ or LiClO _{4 in} a non-aqueous solvent such as ethylene carbonate or propylene carbonate. Fluorine-based polymers and styrene-butadiene copolymers have been used, but in recent years, vinylidene fluoride-based polymers, which have lower specific resistance and good thin film forming properties, have been used as a binder for forming a negative electrode. Lithium ion secondary batteries have been put to practical use.

On the other hand, most of the fluorine-based resins that have been put to practical use as binders for positive electrodes of non-aqueous batteries are tetrafluoroethylene polymers (powder molding type or paste type). It has also been proposed to use a fluororubber composed of a vinylidene fluoride copolymer (Japanese Patent Laid-Open Nos. 4-95363 and 7-22072).
No. 0).

[0005]

There is one important problem in using a vinylidene fluoride polymer as a binder for forming a positive electrode, particularly for a slurry type mixture.
For example, at the stage of preparing a positive electrode mixture slurry using a lithium-based mixed metal oxide as an active material, the slurry often gels (in extreme cases, gelation occurs within a few minutes), and once gelled. Even if the slurry is heated or a new solvent is added, only a non-uniform slurry is obtained, and as a result, it becomes very difficult to apply the mixture slurry to the current collector.

The above-mentioned gelation causes almost no problem with the mixture slurry for forming a negative electrode, which uses carbon having low chemical activity, except when an ultrahigh molecular weight vinylidene fluoride polymer is used. From this, it is expected that the lithium-based composite metal oxide acts on the gelation of the vinylidene fluoride-based polymer in the mixture slurry for forming the positive electrode, and this tendency is particularly apparent as a conductive additive. It is promoted when carbon black is added.

Therefore, a main object of the present invention is to provide a stable electrode mixture for forming a positive electrode for a non-aqueous battery, which contains a vinylidene fluoride polymer as a binder and prevents its gelation.

Another object of the present invention is to provide a non-aqueous battery including the positive electrode thus formed.

[0009]

According to the research conducted by the present inventors, the gelation of the vinylidene fluoride polymer in the above-mentioned mixture slurry for forming a positive electrode for a non-aqueous battery is caused by an organic acid in the mixture. Was found to be effectively suppressed by adding

The electrode mixture for non-aqueous batteries of the present invention is based on such knowledge, and is composed of an electrode active material composed of a composite metal oxide, a conduction aid, a vinylidene fluoride polymer and an organic solvent. It is characterized in that an organic acid is added to the mixture.

The non-aqueous battery of the present invention is characterized by having an electrode active material made of a composite metal oxide, a conductive auxiliary agent, and a positive electrode made of a vinylidene fluoride polymer stabilized by an organic acid. Is.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A lithium-based composite metal oxide used as an electrode active material in an electrode mixture for a non-aqueous battery of the present invention has a general formula of LiMO ₂ (M is Co, Ni, F).
e, Mn, Cr, at least one of transition metals such as V), and preferable examples thereof include LiCoO ₂ , LiNiO ₂ , and LiNi _x Co _1-x.
O ₂ or spinel type LiMn ₂ O ₄ may, for example, be mentioned. Among them, LiNi _x Co _1-x O ₂ (0 ≦ x ≦
The Li-Co or Li-Ni binary or Li-Ni-Co ternary composite metal oxide represented by 1) is particularly preferably used because it has a high charge / discharge potential and excellent cycle characteristics.

The conductive additive is added for the purpose of improving the conductivity of the electrode mixture layer when an active material having a low electron conductivity such as LiCoO ₂ is used. Carbon black,
Carbonaceous substances such as graphite fine powder or fibers, metal fine powder such as nickel and aluminum, or fibers are used. Among them, conductive carbon black (which has an average particle diameter of about 10 to 100 nm as observed by an electron microscope) having a large conductivity improving effect but also having a large gelling promoting effect on a vinylidene fluoride-based polymer is preferably used. The effect of the present invention is particularly remarkable when used alone or in combination with other conductive auxiliary agents. These conductive aids are complex metal oxides 1
It is preferably added in an amount of 0.1 to 10 parts by weight with respect to 00 parts by weight.

The vinylidene fluoride-based polymer used in the present invention includes vinylidene fluoride homopolymers, copolymers and modified products thereof. A vinylidene fluoride homopolymer is preferable from the viewpoint of durability against a non-aqueous electrolyte, particularly swelling resistance. However, since the adhesion to an electrode substrate such as a metal is slightly insufficient, it is more preferable to use a copolymer with another monomer, particularly a monoester of an unsaturated dibasic acid, vinylene carbonate or an epoxy-containing vinyl monomer. A copolymer in which a polar group such as a carbonyl group, a carboxyl group or an epoxy group is introduced by copolymerization with a polymer or the like (JP-A-6-172452, etc.) is preferably used. Also, in a solvent that dissolves or swells a vinylidene fluoride homopolymer or a copolymer, a silane coupling agent having both a vinylidene fluoride polymer such as an amino group or a mercapto group, a reactive group and a hydrolyzable group. Alternatively, a modified vinylidene fluoride-based polymer obtained by treatment in a titanate-based coupling agent (JP-A-6-93025).
No.) is also preferably used. However, in order to maintain good swelling resistance to the non-aqueous electrolyte as a whole, it is preferable to maintain the untreated vinylidene fluoride unit in a range of 90 mol% or more, particularly 95 mol% or more.

The vinylidene fluoride polymer has an intrinsic viscosity (logarithmic viscosity at 30 ° C. of a solution of 4 g of resin dissolved in 1 liter of N, N-dimethylformamide)
0.5 or more, furthermore 0.5 to 20.0, especially 0.8 to 1
Preferably, it has a value in the range of 5.0.

The vinylidene fluoride polymer is 0.1 to 20 parts by weight, especially 1 part by weight, relative to 100 parts by weight of the composite metal oxide and the conductive additive (these are collectively referred to as "powder electrode material"). It is preferably used in a proportion of from 10 to 10 parts by weight.

As the organic solvent used in the present invention, one having a function of dissolving the above vinylidene fluoride polymer is used, preferably a polar solvent such as N-
Methyl-2-pyrrolidone, dimethylformamide,
Examples include N, N-dimethylacetamide, N, N-dimethylsulfoxide, hexamethylphosphoamide, dioxane, tetrahydrofuran, tetramethylurea, triethylphosphate, trimethylphosphate, and the like.

These organic solvents are used singly or as a mixture of two or more kinds in an amount of 0.1 to 30 parts by weight, particularly 1 to 15 parts by weight of vinylidene fluoride polymer per 100 parts by weight of the organic solvent. Preferably.

According to the present invention, an organic acid is further added to the electrode mixture. Examples of preferably used organic acids include
Acrylic acid, formic acid, citric acid, acetic acid, oxalic acid, lactic acid,
Pyrupic acid, malonic acid, propionic acid, maleic acid, citraconic acid, butyric acid and the like can be mentioned. Among them, maleic acid, citraconic acid, etc., which are cis-type dibasic acids, or malonic acid is particularly preferably used. These organic acids are contained in the positive electrode mixture slurry per 100 parts by weight of the composite metal oxide,
It is preferably used in an amount of 0.001 to 5 parts by weight, particularly 0.01 to 0.5 parts by weight. Many of these organic acids have a relatively high vapor pressure, and even if they are added excessively, they are considerably removed in the process of applying the mixture and forming the electrode. I won't. Also, unlike inorganic acids such as hydrochloric acid and sulfuric acid, it does not have a strong acid action to the extent that it reacts with the electrode active material, and even if it remains in the formed electrode, it becomes lithium carbonate, which adversely affects the battery characteristics. Do not give. Further, there is a tendency that the vinylidene fluoride polymer remains in the electrode to improve the electrode characteristics through the stabilization of the vinylidene fluoride polymer.

The organic acid is added by adding the acid of the electrode mixture slurry.
It is also understood that it also has a role of adjusting alkalinity. Although it is difficult to directly measure the acidity-alkalinity of a slurry that is an organic solvent solution, it is difficult to directly measure the acidity-alkalinity by using ion exchange water.
It is convenient to measure the pH of the double dilution, which is 9
It is preferable to add the organic acid so that it will be 7.5 or less.

The method of incorporating the organic acid in the positive electrode mixture is basically arbitrary, and a method of mixing it simultaneously with the positive electrode active material, carbon black, vinylidene fluoride polymer and organic solvent is also possible. Preferably, a vinylidene fluoride-based polymer solution to which an organic acid has been added (more preferably, by dissolving the vinylidene fluoride-based polymer in an organic solvent to which an organic acid has been added), and this solution and the positive electrode active material It is preferable to form a positive electrode mixture slurry by mixing with a powder electrode material such as.

The positive electrode mixture slurry formed as described above is treated with a metal foil or metal mesh of iron, stainless steel, steel, copper, aluminum, nickel, titanium or the like, for example, as shown in the sectional view of FIG. Consisting of 5 to 100μ thick
m, in the case of a small scale, it is applied to at least one side, preferably both sides, of the current collector 11 having a thickness of, for example, 5 to 20 μm, and dried at 50 to 170 ° C. ~ 1000 μm electrode mixture layer 12a, 1
By forming 2b, the positive electrode 10 for a non-aqueous battery is formed.

FIG. 2 is a partially exploded perspective view of a lithium secondary battery as an example of the non-aqueous battery of the present invention including the positive electrode thus formed.

That is, this secondary battery is basically a positive electrode 1 and a negative electrode 2 with a separator 3 made of a microporous film of a polymer substance such as polypropylene or polyethylene impregnated with an electrolytic solution, arranged and laminated. The power generating element having a spirally wound structure is housed in a bottomed metal casing 5 forming the negative electrode terminal 5a. In this secondary battery, the negative electrode is further electrically connected to the negative electrode terminal, and the gasket 6 and the safety valve 7 are arranged at the top, and then the positive terminal 8a electrically connected to the positive electrode 1 at the convex portion. The plate 8 is arranged, the top rim 5b of the casing 5 is caulked, and the entire structure is sealed. The positive electrode 1 shows the structure of the electrode structure 10 shown in FIG. 1, for example.

The negative electrode 2 can also be basically formed as an electrode structure having a laminated structure similar to that of the positive electrode. For example,
In the positive electrode mixture of the present invention, instead of the positive electrode active material or the positive electrode active material and the conductive additive, for example, graphite, activated carbon or a negative electrode mixture using a carbonaceous material obtained by firing and carbonizing a phenol resin, pitch or the like as an electrode active material. An electrode structure in which a negative electrode is formed by applying the agent to one surface or both surfaces of the current collector and drying the same is preferably used.

As the non-aqueous electrolytic solution with which the separator 3 is impregnated, for example, a solution obtained by dissolving an electrolyte such as a lithium salt in a non-aqueous solvent (organic solvent) can be used.

Here, as the electrolyte, LiPF ₆ , Li
AsF ₆ , LiClO ₄ , LiBF ₄ , CH ₃ SO ₃ L
i, CF ₃ SO ₃ Li, LiCl, LiBr and the like.
Further, as the organic solvent of the electrolyte, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl propionate, ethyl propionate. , And a mixed solvent thereof are used, but not limited thereto.

Although an example of the cylindrical battery is shown in the above, the non-aqueous battery of the present invention can be configured as a coin battery, a prismatic battery or a paper battery.

[0029]

The present invention will be described more specifically with reference to examples and comparative examples.

Example 1 LiNi _0.8 C as an active material
o _0.2 O ₂ (average particle size 15 μm) 9 parts by weight, conductive carbon black (average particle size about 40 nm, specific surface area 30)
m ² / g, oil absorption 129 ml / 100 g) 0.7 part by weight, vinylidene fluoride polymer (KF polymer # 130)
0: 0.3 part by weight of Kureha Chemical Industry Co., Ltd. and 6 parts by weight of N-methyl-2-pyrrolidone containing 0.1% by weight of maleic acid were mixed and uniformly dispersed at 50 ° C. To prepare a positive electrode mixture slurry. This mixture slurry was stored at room temperature and showed almost the same viscosity even after 24 hours, and was applied to one surface of a copper foil having a thickness of 10 μm and dried at 130 ° C. to form a positive electrode layer having a smooth thickness of 100 μm. A structure was obtained.

Example 2 LiNi _0.9 C as an active material
o _0.1 O ₂ (average particle size 15 μm) 9 parts by weight, conductive carbon black 0.7 parts by weight, vinylidene fluoride polymer (KF polymer # 1300: manufactured by Kureha Chemical Industry Co., Ltd.)
And 6 parts by weight of N-methyl-2-pyrrolidone to which 0.1% by weight of citraconic acid was added and uniformly dispersed at 50 ° C. to prepare a positive electrode mixture slurry. The mixture slurry was stored at room temperature and showed almost the same viscosity after 24 hours, and was applied to one side of a copper foil having a thickness of 10 μm.
By drying at 130 ° C., an electrode structure having a smooth positive electrode layer and a total thickness of 105 μm was obtained.

Example 3 A positive electrode mixture slurry was prepared in the same manner as in Example 1 except that 6 parts by weight of N-methyl-2-pyrrolidone containing 0.1% by weight of malonic acid was used. This mixture slurry showed almost the same viscosity even after being stored at room temperature for 24 hours, was applied to one side of a copper foil having a thickness of 10 μm, and was dried at 130 ° C. to form an electrode structure having a smooth positive electrode layer (total: A thickness of 102 μm) was obtained.

Example 4 A positive electrode mixture slurry was prepared in the same manner as in Example 1 except that 6 parts by weight of N-methyl-2-pyrrolidone containing 0.1% by weight of acetic acid was used. This mixture slurry showed almost the same viscosity even after being stored at room temperature for 24 hours, was applied to one side of a copper foil having a thickness of 10 μm, and was dried at 130 ° C. to form an electrode structure having a smooth positive electrode layer (total: A thickness of 106 μm) was obtained.

(Comparative Example 1) N-without addition of maleic acid
A positive electrode mixture slurry was prepared by mixing and dispersing in the same manner as in Example 1 except that methyl-2-pyrrolidone was used.

This slurry was violently gelated during storage at room temperature for 2-3 hours after preparation, making it difficult to apply to copper foil.
After 4 hours, it became a hard pudding and could not be used.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an electrode structure used in a non-aqueous battery.

FIG. 2 is a partially exploded perspective view of a non-aqueous solvent secondary battery that can be configured according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 5 Casing (5a: bottom part, 5b: rim) 6 Gasket 7 Safety valve 8 Top plate 10 Electrode structure 11 Current collectors 12a, 12b Electrode mixture layer

Claims (5)

[Claims] 1. An electrode mixture for a non-aqueous battery, which is obtained by adding an organic acid to a mixture containing an electrode active material composed of a composite metal oxide, a conductive aid, a vinylidene fluoride polymer and an organic solvent. 2. The vinylidene fluoride-based polymer is a copolymer of 95 mol% or more of vinylidene fluoride and another monomer, or a vinylidene fluoride homopolymer or a modified product of the copolymer. Electrode mixture. 3. The electrode active material is LiNi _x Co _1-x O
The electrode mixture according to claim 1, which is composed of a composite metal oxide represented by ₂ (O ≦ x ≦ 1). 4. The electrode mixture according to claim 1, wherein the conductive additive is carbon black. 5. A non-aqueous battery having an electrode active material composed of a composite metal oxide, a conductive additive, and a positive electrode composed of a vinylidene fluoride polymer stabilized with an organic acid.