JPH06150906A - Nonaqueous secondary battery - Google Patents

Abstract

PURPOSE:To provide a nonaqueous secondary battery having a less rise in the overvoltage of an electrode, regardless of repeated service. CONSTITUTION:An aqueous dispersing element of a non-fluorine organic polymer is added to a positive active material made of a transition metal compound capable of storing and releasing lithium ions, thereby preparing slurry. Then, this slurry is dried after application to a base material such as current collector metal, thereby providing a thin film and large area electrode adhering to the surface of the base material. This electrode is used as a positive electrode.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a non-aqueous secondary battery.

[0002]

2. Description of the Related Art In recent years, electronic devices have been remarkably reduced in size and weight, and accordingly, there has been a great demand for reduction in size and weight of batteries serving as power sources. Non-aqueous batteries have been attracting attention because it is impossible to meet the above requirements with conventional batteries using general aqueous electrolytes.

Such a non-aqueous battery has excellent performance in terms of size and weight reduction, and is a primary battery represented by a lithium battery, lithium / titanium disulfide secondary battery, carbon /
LiCoO ₂ secondary batteries and the like have been proposed, and some of them have already been put to practical use. As described above, the non-aqueous secondary battery is excellent in performances such as high energy density and small size and light weight, but has a drawback in output characteristics as compared with the aqueous battery.

As a general method of molding an electrode, an electrode active material and an organic polymer are mixed and compression molded. In the case of such a method, the effect of the organic polymer binder, which is an insulating substance, on the electrode active material is relatively small, and the type and shape of the binder used are also limited, but on the other hand, a thin film and a large area electrode can be used. It is extremely difficult to manufacture.

On the other hand, in the organic electrolyte secondary battery, attempts have been made to reduce the thickness of the electrode and increase the area of the electrode in order to improve the output characteristics.
As such a method, a method is known in which an electrode active material is dispersed in an organic solvent solution of an organic polymer, and then the electrode is molded by coating and drying it on a substrate. According to this method, a thin film and a large-area electrode can be easily obtained, but the influence of the binder, which is an insulating organic polymer, on the electrode active material is significantly large. For example, a part of the active material is coated with the binder, Problems such as low battery capacity and increased electrode overvoltage tend to occur. In particular, in the case where the active material undergoes a volume change when absorbing and releasing Li ions, the active material may be partially peeled from the current collector, or may be dissolved in an organic solvent depending on the properties of the organic polymer binder. In the coating method, the binder has a strong affinity with the electrolytic solution, and swelling tends to cause poor contact between the active materials, which is also a cause of increase in overvoltage. Under such circumstances, there has been a demand for an electrode that does not cause an increase in overvoltage even when repeatedly charged and discharged.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a high performance secondary battery.

[0007]

Means for Solving the Problems As a result of a detailed study of the coating performance of a mixed dispersion of a transition metal compound and a non-fluorine type organic polymer capable of occluding and releasing Li ions, the present inventors have found that When a slurry solution obtained by mixing and dispersing a transition metal compound capable of occluding and releasing Li ions in a slurry solution in which the coalescence is finely dispersed in an aqueous solvent is applied and dried on a metal substrate such as aluminum, the adhesiveness to the substrate is also good, The inventors have found that it is a method for obtaining an excellent electrode without causing an increase in overvoltage even when it is used as an electrode, and completed the present invention.

That is, according to the present invention, in a non-aqueous secondary battery comprising a positive electrode, a negative electrode, and an organic electrolyte solution containing a lithium salt, a positive electrode active material comprising a transition metal compound capable of inserting and extracting lithium ions and a non-fluorine-containing organic material. It is intended to provide a non-aqueous secondary battery characterized by using a positive electrode obtained by applying a slurry comprising a polymer aqueous dispersion onto a substrate and drying the same.

The non-fluorine-based organic polymer aqueous dispersion of the present invention is, for example, an ethylene / acrylic acid (salt) copolymer, an acrylic polymer, a vinyl polymer, or a styrene / butadiene rubber of 10 μm or less. Particles, preferably 5μ
A dispersion in an aqueous dispersion medium containing particles of m or less, more preferably 1 μm or less. Usually such an aqueous dispersion is industrially produced by a method of directly producing an aqueous dispersion by polymerizing a monomer by an emulsion polymerization method, or a method of redispersing a polymer or a copolymer in water. . The polymers in these dispersions have a low affinity with the electrolytic solution and are preferably those which do not easily swell in the electrolytic solution. For example, in the case of polymerization, such as partially cross-linking by partially using a bifunctional or higher monomer. Methods can also be used. There is an aqueous dispersion of polytetrafluoroethylene in the aqueous dispersion of the polymer, which is used as a binder for compression molding electrodes, but when used in this method, the adhesiveness to a metal substrate is weak and unsuitable. Is.

The polymer used in the present invention is a positive electrode active material 100.
It is preferable to use 0.5 to 10 parts by weight, more preferably 1 to 5 parts by weight, based on parts by weight. If it is less than 0.5 parts by weight, the adhesive strength between the active materials and the metal base material will be weak, and if it is more than 10 parts by weight, the resistance of the electrode will be large, such being undesirable. The composition of the slurry is not particularly limited, but usually the electrode active material 10
The dispersion medium is in the range of 20 to 150 parts by weight, preferably 25 to 100 parts by weight, relative to 0 parts by weight. The slurry of the present invention is composed of an aqueous dispersion of a positive electrode active material and a non-fluorine-based organic polymer, but does not necessarily exclude components other than this, for example, a small amount of thickener for slurry viscosity adjustment,
Various additives such as a binding aid can also be added.

The positive electrode active material of the present invention is not particularly limited as long as it can occlude and release lithium. For example, manganese oxide, vanadium oxide, iron oxide, lithium manganese composite oxide, lithium vanadi The above, in which a part of the transition metal is replaced with a titanium complex oxide, a lithium cobalt complex oxide, a lithium nickel complex oxide, a lithium cobalt nickel complex oxide, a molybdenum oxide, a titanium sulfide, or another transition metal or a typical metal. Compound,
For example, a lithium cobalt tin compound (JP-A-62-9)
No. 0863).

When assembling a non-aqueous battery using the battery electrode of the present invention, the electrolyte of the non-aqueous electrolyte is not particularly limited, but as an example, LiClO ₄ , LiBF ₄ ,
LiAsF ₆ , CF ₃ SO ₃ Li, LiPF ₆ , LiN
(SO ₃ CF ₃ ) ₂ , LiI, LiAlCl ₄ , NaC
10 ₄ , NaBF ₄ , NaI, (n-Bu) ₄ NClO
₄ , (n-Bu) ₄ NBF ₄ , KPF _{6 and the} like.

Examples of the organic solvent for the electrolytic solution used include ethers, ketones, lactones, nitrites, amides, sulfur compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds and phosphorus. Acid ester compounds, sulfolane compounds and the like can be used, and among these, ethers, ketones, nitriles, lactones, carbonates and sulfolane compounds are preferable.

As typical examples of these, tetrahydrohylan, 2-methyltetrahydrofuran, 1,4-dioxane, monoglyme, acetonitrile, propionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzonitrile, 1, 2-dichloroethane, γ-butyrolactone, dimethoxyethane, ethyl acetate, propylene carbonate, ethylene carbonate,
Examples thereof include dimethylformamide, dimethylsulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfolane, trimethyl phosphate, triethyl phosphate, and mixed solvents thereof, but are not necessarily limited thereto.

The negative electrode material to be used is not particularly limited, but examples thereof include lithium, alloys of metals other than lithium and lithium, petroleum pitch coke, artificial graphite, natural graphite, mesophase microbeads, vapor grown carbon. Examples include carbonaceous materials such as fibers. In the present invention, the positive electrode active material is applied and dried as a slurry-like coating liquid on a substrate together with a non-fluorine-based polymer binder to form a battery electrode. As the base material, a metal base material that also serves as a current collector can be used, and as the current collector, sus, titanium, aluminum or the like is used. When an active material having a high positive electrode potential is used, aluminum or titanium is more preferable. It is suitable. It can be coated on these collector foils, and as such a coating method, an arbitrary coater head such as a reverse roll method, a comma bar method, a gravure method or an air knife method can be used.

The electrode obtained by these methods can be used, if necessary, by further pressing it to increase the density of the active material on the substrate. Further, if necessary, a battery is constructed by using components such as a separator, a collector, a terminal, and an insulating plate. Further, the structure of the battery is not particularly limited, but a positive electrode, a negative electrode, if necessary, a paper type battery having a separator in a single layer or a multilayer, or a positive electrode, a negative electrode, if necessary, a separator roll. An example is a form of a cylindrical battery that is wound into a shape.

[0017]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the invention is not limited thereto.

[0018]

Example 1 LiCo _0.98 Sn _0.02 O having an average particle size of 2 μm
₂ 100 parts by weight of graphite powder 2.5 parts by weight, acetylene black 2.5 parts by weight are mixed, and 6 parts by weight of carboxy-modified styrene / butadiene emulsion [L1571 manufactured by Asahi Kasei Kogyo Co., Ltd.] (solid content 48% by weight) As a thickener, 30 parts by weight of an aqueous carboxymethyl cellulose solution (solid content 1% by weight) was added, and further 5 parts by weight of purified water was added and mixed and stirred to obtain a coating liquid. This coating liquid was applied and dried at a solid content of 270 g / m ^{2 using an} Al foil (thickness 15 μm) as a base material, and pressed to obtain a positive electrode having a thickness of 100 μm.

The positive electrode was cut out into a size of 1 cm × 1 cm, a sus net having Li metal pressure-bonded thereto was used as a negative electrode, and a Li metal was used as a reference electrode. These electrodes were mixed under an Ar gas atmosphere with a mixed solvent of butyrolactone (hereinafter abbreviated as γ-BL) and propylene carbonate (hereinafter abbreviated as PC) (volume ratio of γ-BL: PC = 70: 3).
The battery shown in FIG. 1 was assembled using the electrolytic solution in which LiBF ₄ was dissolved in 0) in 1).

[0020]

Example 2 In Example 1, a carboxy-modified styrene / butadiene emulsion was used as a positive electrode coating solution in a styrene / acrylic emulsion [F2 manufactured by Asahi Kasei Kogyo Co., Ltd.].
A battery was assembled in exactly the same manner except that it was changed to 000).

[0021]

Comparative Example 1 50 parts by weight of a toluene solution of a styrene / butadiene copolymer (4% by weight) as a coating liquid for the positive electrode, 100 parts by weight of the positive electrode active material of Example 1, and graphite powder 2.5.
A battery was assembled in the same manner as in Example 1 except that 1 part by weight and 2.5 parts by weight of acetylene black were mixed to prepare a coating solution.

[0022]

Comparative Example 2 Example 1 was repeated except that 9 parts by weight of an emulsion solution (solid content 60% by weight) in which a tetrafluoroethylene polymer was dispersed in an aqueous medium was used as the coating liquid for the positive electrode instead of the carboxy-modified styrene / butadiene emulsion.
When kneading and stirring in the same manner as above, a gelled state was obtained, the viscosity was high, coating was not possible, and an electrode coated on the Al foil could not be obtained.

The above battery was operated at 25 ° C. at 1 mA (1 mA / c
The cycle of charging to 4.2 V with m ² ) and discharging to 3.0 V was repeated. Table 1 shows the cycle retention rate of overvoltage, charge / discharge efficiency, and discharge capacity in the charge / discharge cycle of this battery. Next, in order to examine the deterioration during high temperature storage, charge and discharge once at 25 ° C and then 60 at 4.2V charge.
Table 2 shows changes in overvoltage after storage for 1 week at ℃.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

EFFECTS OF THE INVENTION By using the positive electrode of the present invention, a non-aqueous secondary battery having a very small increase in overvoltage of the electrode after repeated use and after use at high temperature and having good cycleability can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a configuration example of a battery of the present invention.

[Explanation of symbols]

 1 Working Electrode (Negative Electrode) 2 Counter Electrode (Lithium Metal) 3 Reference Electrode (Lithium Metal) 4 Electrolyte 5 Glass Container 6 Ar Gas

Claims (1)

[Claims] 1. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and an organic electrolytic solution containing a lithium salt, comprising a positive electrode active material comprising a transition metal compound capable of absorbing and releasing lithium ions and a non-fluorine-containing organic polymer. A non-aqueous secondary battery using a positive electrode obtained by applying a slurry comprising an aqueous dispersion onto a substrate and drying the substrate.