JPS63121247A - Negative electrode of secondary battery - Google Patents

Abstract

PURPOSE:To obtain a compact, lightweight power source with particularly excellent cycle characteristics and self-discharging characteristics by increasing the ratio of bonding agent to carbon on an interface where a partial area of active substance layer makes contact with collectors compared with that on the surface of active substance layer. CONSTITUTION:In the negative electrode of a nonaqueous secondary battery, which comprises at least an active substance layer formed by carbon, serving as a negative electrode active substance, and bonding agent and collectors in contact wherewith, the ratio of bonding agent to carbon is increased on an interface where a partial area of active substance layer makes contact with collectors compared with that on the surface of active substance layer. The increased ratio of bonding agent on the interface between carbon active substance layer of negative electrode and collector is remarkably decreased to show stable battery characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a novel secondary battery, and more particularly to a small and lightweight secondary battery.

[Conventional technology] In recent years, electronic devices have become smaller and lighter, and as a result, there is a strong demand for batteries that serve as power sources to be made smaller and lighter.In the field of secondary batteries, lithium batteries and other Although small and lightweight batteries have been put into practical use, since these are secondary batteries, they cannot be used repeatedly, and their fields of application are limited. On the other hand, in the field of secondary batteries, lead batteries and nickel-cadmium batteries have conventionally been used, but both have major problems in terms of miniaturization and weight reduction. From this point of view, non-aqueous secondary batteries have been attracting a lot of attention, but they have not yet been put into practical use.One of the reasons for this is that the electrode active materials used in these secondary batteries have poor cycleability, self-discharge characteristics, etc. The problem is that no material has been found that satisfies practical physical properties.

On the other hand, a new group of electrode active materials that utilize intercalation of layered compounds or doping phenomena, which have a different reaction type from conventional nickel-cadmium batteries, lead-acid batteries, etc., are attracting attention.

Such new electrode active materials do not cause complex chemical reactions during electrochemical reactions during charging and discharging, and are therefore expected to have extremely excellent charge-discharge cycle performance.

Among them, a new secondary battery using carbon as an active material is attracting attention, for example, Japanese Patent Application Laid-Open No. 58-3588
1. #Kaikai59-173979, Unexamined Japanese Patent Publication No. 58-20
7588, JP-A-58-209884, JP-A-81-
No. 111907, and also the patent application ShoE by the present inventors.
It has been proposed to use various carbons as active materials, such as No. II-103785 No. 1, and its practical application is expected.

However, although carbon has superior conductivity compared to other conventional active materials, it surprisingly has a large contact resistance at the interface with a current collector, which poses a major problem when actually used as an electrode. It had become.

[Problems to be Solved by the Invention] As mentioned above, secondary batteries using carbon as an active material still have problems such as an increase in internal resistance. This phenomenon is particularly remarkable when carbon is used as the negative electrode active material.

[Means and effects for solving the problems] The present invention solves the above-mentioned problems and provides a high-performance, high-energy-density, compact, lightweight secondary battery with excellent battery performance, especially cycleability and output characteristics. It was made for the purpose of

According to the present invention, there is provided a non-aqueous secondary battery negative electrode comprising an active material layer formed of at least carbon as a negative electrode active material and a binder, and a current collector in contact with the active material layer. A non-aqueous secondary battery negative electrode is provided, wherein the ratio of the binder to carbon at the interface of the active material layer in contact with the current collector is larger than the ratio of the binder to carbon at the surface of the active material layer. Ru.

The carbon used in the present invention includes, but is not particularly limited to, carbon whiskers obtained by carbonizing activated carbon, phenol resin carbide, condensed polycyclic hydrocarbons, or polycyclic heterocyclic compounds, as disclosed in the above-mentioned publications, etc. Examples include carbon fiber, vapor grown carbon fiber, needle coke, and pitch coke.

Examples of binders include, but are not limited to, polyethylene, Teflon, butyl rubber, nitrile rubber, styrene/butadiene rubber, polyacrylonitrile, polyvinylidene sulfide, polyvinyl fluoride, styrene/butadiene block copolymers, and hydrogenated carboxylated modified products thereof. etc. are given as an example.

As a current collector, there are no particular limitations, but nickel, copper, SUS
Examples include metal materials such as , titanium, and the like. Further, as for its shape, any shape such as a foil shape, a net shape, a sponge shape, an expanded metal shape, a punched metal shape, etc. can be used.

A common method for forming an electrode by molding an active material, a binder, and a current collector is to mix the active material with a powdery binder such as Teflon powder or polyethylene powder, and then compression mold the mixture.

A more preferable method includes a method of forming an electrode active material using a binder dissolved and/or dispersed in a solvent as a binder. 2 The present invention can also use the method described above.

In the present invention, the ratio of the carbon negative electrode active material to the binder is not particularly limited, but is 0.1 to 15 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of carbon. If it is less than 0.1, the strength of the active material layer is insufficient, causing problems in the battery assembly process. Moreover, if it exceeds 15 parts by weight, it is not preferable because it will have a significant adverse effect on battery performance.

As mentioned above, in the present invention, it is extremely important to increase the ratio of the amount of binder at the interface between the carbon negative electrode active material layer and the current collector, and by using such a structure, the contact resistance between the current collector and the active material layer can be reduced. becomes extremely small and exhibits stable battery performance. The ratio of carbon to binder in such a layer is not particularly limited, but carbon 10
The amount of binder is 20 to 800 parts by weight, preferably 75 to 300 parts by weight per 0 m ti part. If the amount is less than 20 parts by weight, the amount of binder is too small to exhibit the effects of the present invention.
If the amount exceeds 900 parts by weight, the volume electrical resistance of the layer becomes large, which is not preferred.

The thickness of the layer corresponding to the amount of binder is not particularly limited, but is 115 to 1/100 of the thickness of the carbon negative electrode active material layer.

Preferably it is in the range of 1/10 to 1/75.

It is not yet clear why such an effect occurs in a negative electrode that uses carbon as the negative electrode active material, but the first possibility is that increasing the amount of binder at the current collector interface will bond the current collector and the active material. It seems that the adhesive force with the material layer is increasing. Second, common sense suggests that if you increase the amount of binder,
The volume electrical resistance of the layer becomes extremely large and behaves like an insulating layer, but in the case of carbon, unlike other active materials, the drop in volume electrical resistance is thought to be small. The above, first, and second effects are expressed synergistically, resulting in an unexpected effect. This behavior is unique to carbon and is not found in other active materials.

Various methods can be employed to obtain the carbon negative electrode having the structure of the present invention.

Here are some examples: (1) A method in which a mixture or coating agent with a large amount of binder is previously formed on the current collector, and then a layer with a minimum amount of binder is formed.

(2) A method in which only the binder is previously formed on the current collector and then a small layer of the binder is formed. This method is particularly preferred when forming the negative electrode by a coating method.

An example of such a method is as follows. Here, the type of binder and carbon used in the binder amount layer and the binder small layer may be the same or different.

Also, as a matter of course, as a modification of the Bokuto method, there are cases in which there are two or more layers of binder amount, and furthermore, cases in which the binder amount ratio is continuously changed, that is, a concentration gradient is provided. Conceivable.

Furthermore, in the present invention, carbon in a layer with a large amount of binder may or may not actually function as an active material, but this is not a wood-related problem in the present invention.

The reason for this is that the effect of the present invention is that even if the layer containing the binder is thin, it can sufficiently exhibit its function.

As mentioned above, it exhibits particularly excellent performance when used as a negative electrode, but the positive electrode used at this time is not particularly limited, but as an example, Tl52@Ti53. MO8
3, Fl! S2. Lin-x) Mn02. Liu-
x) co02+Lin-x) Old 02. V2O5, Li
(+-x)co, 5nz0? +V6O13 is mentioned.

Basic components for assembling the non-aqueous secondary battery of the present invention include an electrode using the active material of the present invention, a separator, and a non-aqueous electrolyte. Separators include, but are not limited to, woven fabrics, non-woven fabrics, glass woven fabrics,
Examples include synthetic resin microporous membranes, but as mentioned above, when using thin membranes and large-area electrodes, 1, for example, JP-A-58-5
The synthetic resin microporous membrane disclosed in No. 9072, particularly the polyolefin microporous membrane, is preferable in terms of thickness, strength, and membrane resistance.

The electrolyte of the non-aqueous electrolyte is not particularly limited, but examples include: LiC1'On, LiBFn, LiAs
F6゜CF3SO3Li, LiPF6. LiI,
LiA1'Gj! 4. NaC1'04゜NaBFn,
Mal, (n-nu)4N”(j)On, (n-
Bu)4N@BFa.

Examples include KPF b. Examples of organic solvents used in the electrolytic solution include ethers, ketones, lactones, nitriles, amines, and amides.

Sulfur compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds, phosphate ester compounds, sulfolane compounds, etc. can be used, but among these, ethers, ketones, nitriles, chlorinated Hydrocarbons, carbonates, and sulfolane compounds are preferred, and cyclic carbonates are more preferred.

Representative examples of these include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, acetonitrile, propionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzoni) IJ, IL/, 1.2
-dichloroethane, γ-butyrolactone, dimethoxyethane, methylformate, propylene carbonate,
ethylene carbonate.

Examples include vinylene carbonate, dimethylformamide, dimethyl sulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfolane, trimethyl phosphate, triethyl phosphate, and mixed solvents thereof, but are not necessarily limited to these. .

Furthermore, if necessary, the battery is constructed using parts such as a current collector, a terminal, and an insulating plate. In addition, the structure of the battery is not particularly limited, but it may include a paper type battery with a positive electrode, a negative electrode, and, if necessary, a separator in a single layer or a multilayer.[7
! Examples include a cylindrical battery in which a positive electrode, a negative electrode, and, if necessary, a separator are wound into a roll.

[Effects of the Invention] The battery of the present invention is small and lightweight, has particularly excellent cycle characteristics and self-discharge characteristics, and is extremely useful as a power source for small electronic devices, electric vehicles, power storage, and the like.

[Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

One dollar coke (KOA-9J-Coke manufactured by Koa Oil Co., Ltd.) was used as an example.
) The following two coating solutions were prepared using powder with an average particle size of 10 IL.

Table 1 (Parts by weight) The above coated lacquer was coated on a 10l copper foil using a roll coater and dried to form a layer having a thickness of 12l. Thereafter, the above coating solution (1) was applied onto the layer using a roll coater and dried to obtain a negative electrode having a total thickness of 175 μl. In this negative electrode, the active material was firmly adhered to the current collector.

The contact resistance between the current collector and the active material layer of this negative electrode was 8.1 ohms per 10 ohms.

Moreover, using this negative electrode, LiCoO2 was used as a positive electrode.

The overvoltage of a 1.0 M lithium perchlorate propylene carbon battery at a current density of 1.0 mA/c Oboro2 is 0.
It was 0.03 ohm.

Example 2 The needle coke of the coated lacquer in Example 1 was replaced with carbon black (Raven 41 manufactured by Columbia Carbon Co., Ltd.).
The same operation was performed except that G) was used to form a layer having a film thickness of 3IL, and the same operation was performed thereafter, and the results of the characteristic evaluation of the obtained negative electrode are shown in Table 2.

This negative electrode was firmly adhered to the current collector.

Example 3 Using a coating liquid in which 100 parts by weight of needle coke for coating lacquer in Example 1 was reduced to 0 parts by weight, a layer having a thickness of 2 wells was formed, and the same operation was performed to obtain the obtained negative electrode. The evaluation results of the characteristics are shown in Table 2. This negative electrode was firmly adhered to the current collector.

Example 4 On top of this, a mixture consisting of 100 parts by weight of needle coke powder and 8 parts by weight of polyethylene powder used in Example 1 was compressed and formed to obtain a negative electrode having a total film thickness of 350 mm.

The characteristics evaluation results of this negative electrode are shown in Table 2. This negative electrode was firmly adhered to the current collector.

Comparative Example 1.2 A negative electrode was produced by performing the same operations as in Examples 1 and 4 without forming a film by coating lacquer.

The characteristics evaluation results of this negative electrode are shown in Table 2. All of these negative electrodes had weak adhesion to the current collector, and the active material was easily peeled off.

(Hereafter, the rest are white) Table 2

Claims (1)

[Claims] (1) A non-aqueous secondary battery negative electrode comprising an active material layer formed of at least carbon as a negative electrode active material and a binder, and a current collector in contact with the active material layer, the active material layer A negative electrode for a non-aqueous secondary battery, characterized in that the ratio of the binder to carbon at the interface of the portion in contact with the current collector is greater than the ratio of the binder to carbon at the surface of the active material layer.