JPH0782839B2 - Secondary battery negative electrode - Google Patents

Description

The present invention relates to a novel secondary battery, and further to a small and lightweight secondary battery.

[Prior 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. In the field of primary batteries, small and lightweight batteries such as lithium batteries have already been put into practical use, but since they are primary batteries, they cannot be repeatedly used, and their fields of use have been limited. On the other hand, lead batteries and nickel-cadmium batteries have been conventionally used in the field of secondary batteries, but both have serious problems in terms of size reduction and weight reduction.
From this viewpoint, non-aqueous secondary batteries have received a great deal of attention, but they have not yet been put to practical use. One of the reasons is that no electrode active material used for the secondary battery has been found to satisfy practical physical properties such as cycle characteristics and self-discharge characteristics.

Meanwhile, a new group of electrode active materials utilizing intercalation of a layered compound or a doping phenomenon, which is a reaction mode which is essentially different from that of conventional nickel-cadmium batteries, lead batteries and the like, has been attracting attention.

Such a new electrode active material does not cause a complicated chemical reaction in the electrochemical reaction during charging and discharging, and therefore is expected to have an extremely excellent charge / discharge cycle property.

Of particular interest are novel secondary batteries using carbon as an active material, such as JP-A-58-35881, JP-A-59-173979, JP-A-59-207568, and JP-A-58-20986.
4, JP-A-61-111907, and Japanese Patent Application No. 61-103785 by the present inventors, it has been proposed to use various carbons as the active material, and its practical application is expected. .

However, despite the fact that carbon is superior in electrical conductivity to other conventional active materials, the contact resistance at the interface with the current collector is surprisingly large, which causes a serious problem when actually used as an electrode. Has become.

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

[Means and Actions for Solving Problems] The present invention solves the problems described above, and provides a small-sized and lightweight secondary battery having high performance, high energy density, excellent battery performance, particularly cycleability and output characteristics. It was done for good.

According to the present invention, there is provided a nonaqueous secondary battery negative electrode comprising an active material layer formed of at least carbon as a negative electrode active material and a binder as constituent elements, and a current collector in contact with the active material layer. The weight ratio of the binder to carbon at the interface of the portion of the material layer in contact with the current collector is 0.2 to 9, and the weight ratio of the binder to carbon on the surface of the active material layer is 0.00.
Provided is a negative electrode for a non-aqueous secondary battery, wherein the negative electrode is 1 to 0.15.

The carbon used in the present invention is not particularly limited, but activated carbon disclosed in the above publications, a phenol resin carbide, a carbon whisker obtained by carbonizing a condensed polycyclic hydrocarbon or a polycyclic heterocyclic compound, carbon Fiber, vapor grown carbon fiber, needle coke, pitch cask, etc. are mentioned as the example.

The binder is not particularly limited, but polyethylene, Teflon, butyl rubber, nitrile rubber, styrene / butadiene rubber, polyacrylonitrile, polyvinylidene fluoride, polyvinyl fluoride, styrene / butadiene block copolymer and its hydrogenated carboxylated modification Etc. are mentioned as an example.

The current collector is not particularly limited, but nickel, copper, SUS,
A metal material such as titanium is given as an example. As the shape, any shape such as a foil shape, a net shape, a sponge shape, an expanded metal, a punching metal or the like can be used.

As a method of molding an active material, a binder and a current collector to form an electrode, a method of mixing the active material with a powdery binder such as Teflon powder or polyethylene powder and compression molding is generally used.

A more preferable method is a method of molding an electrode active material using a binder dissolved and / or dispersed in a solvent as a binder.

The present invention can use any of the above methods.

In the present invention, the ratio of the carbon negative electrode active material and the binder needs to be 0.1 to 15 parts by weight (weight ratio of 0.001 to 0.15) relative to 100 parts by weight of carbon, preferably 0.5 to
It is 10 parts by weight (weight ratio 0.005-0.1). When it is less than 0.1, the strength of the active material layer is insufficient, which causes trouble in the battery assembly process. On the other hand, if the amount exceeds 15 parts by weight, the battery performance is significantly adversely affected, which is not preferable.

As described above, in the present invention, it is extremely important to increase the ratio of the amount of the 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 is increased. Becomes extremely small, and stable battery performance is exhibited. The ratio of carbon to binder in this layer is 100 parts by weight of carbon to 2 parts of binder.
It should be 0 to 900 parts by weight (0.2 to 9 by weight ratio), preferably 75 to 300 parts by weight (0.75 to 3 by weight ratio).
Is. If it is less than 20 parts by weight, the amount of the binder is too small to exert the effect of the present invention. On the other hand, when the amount exceeds 900 parts by weight, the volume electric resistance of such a layer becomes large and the opposite effect occurs, which is not preferable.

The thickness of such a large binder layer is not particularly limited, but is 1/5 to 1/100 of the carbon negative electrode active material layer, preferably 1/10 to
It is in the range of 1/75.

Although it is not yet clear why such an effect is exhibited in the negative electrode using carbon as the negative electrode active material, the first conceivable thing is to increase the amount of the binder at the interface of the current collector so that It seems that the adhesive strength with the material layer is increasing. Secondly, it is usually common sense to increase the amount of binder,
The volume electric resistance of the layer itself becomes remarkably large, and it behaves like an insulating layer. However, in the case of carbon, unlike the other active materials, it seems that the volume electric resistance is less reduced. The above-mentioned first and second effects are synergistically expressed, and an unexpected effect is expressed. This is a unique behavior of carbon that 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.

To give some examples, (1) A method of forming a layer having a small amount of binder after forming it on a current collector in advance using a mixture or coating agent having a large amount of binder.

(2) A method in which only the binder is formed on the current collector in advance, and then the binder-small layer is formed. This method is particularly preferable when the negative electrode is formed by a coating method.

As an example of such a method. Here, the types of binder and carbon used in the layer having a large binder and the layer having a small binder may be the same or different.

Also, as a matter of course, as one modification of this method, when there are two or more layers having a large binder, or when the binder amount ratio is continuously changed, that is, when a concentration gradient is provided, etc. Conceivable.

Further, the carbon of the layer having a large binder in the present invention may or may not actually function as an active material, but it is not an essential problem in the present invention.

The reason is that the effect of the present invention is that the layer having a large binder has a sufficient function even if the layer is thin.

As described 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, TiS ₂ , TiS ₃ , MoS ₃ , FeS ₂ , Li _{(1 -x)} M
nO ₂ , Li _(1-x) CoO ₂ , Li _(1-x) NiO ₂ , V ₂ O ₅ , Li _(1-x) Co _y Sn _z O ₂ , V
₆ O ₁₃ can be mentioned.

The basic constituent elements 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 electrolytic solution. The separator is not particularly limited, but may be woven cloth, non-woven cloth, glass cloth,
Examples thereof include synthetic resin microporous membranes. As described above, when a thin film or a large area electrode is used, for example, JP-A-58-59
The synthetic resin microporous membrane disclosed in No. 072, particularly a 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 an example
, LiClO_Four, LiBF_Four, LiA_SF₆, CF₃SO₃Li, LiPF₆, LiI, L
iAlCl_Four, NaClO_Four, NaBF_Four, NaI, (n-Bu)_FourN ClO_Four, (N-B
u)_FourN BF_Four, KPF₆Etc. Also used electrolysis
Examples of the organic solvent of the liquid include ethers, ketones, and
Cutones, nitriles, amines, amides, sulfur compounds
Products, chlorinated hydrocarbons, esters, carbonates,
Nitro compounds, phosphate compounds, sulfolane compounds
Compounds and the like can be used.
Ethers, ketones, nitriles, chlorinated hydrocarbons,
Carbonates and sulfolane compounds are preferable. Further
Preferred are cyclic carbonates.

As typical examples of these, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, acetonitrile, propionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzonitrile, 1,2- Dichloroethane, γ-butyrolactone, dimethoxyethane, methyl formate, propylene carbonate, ethylene carbonate, vinylene carbonate, dimethylformamide, dimethylsulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfolane, trimethyl phosphate, trimethyl phosphate, and triethyl phosphate thereof. Examples of the mixed solvent include, but are not necessarily limited to, these.

Furthermore, a battery is constructed using components such as a current collector, terminals, and an insulating plate. Further, the structure of the battery is not particularly limited, a positive electrode, a negative electrode, if necessary, a paper type battery having a single layer or multiple layers of a separator, a laminated battery,
Alternatively, a positive electrode, a negative electrode, and if necessary, a form of a cylindrical battery in which a separator is wound in a roll shape or the like can be given.

[Effects of the Invention] The effects of the present invention are listed below.

(1) Since the negative electrode of the present invention has a high binder content at the interface of the active material layer on the side of the current collector, the contact resistance between the two is small. The internal resistance of can be suppressed low.

(2) In general, the active material layer of the secondary battery negative electrode repeats expansion and contraction due to intercalation / deintercalation of cations with charge and discharge. Since the active material layer of the negative electrode of the present invention has a high content of the binder at the current collector side interface as described above, it is possible to strongly integrate the active material layer and the current collector, and thus the expansion and contraction It is possible to prevent the contact resistance between the active material layer and the current collector from peeling off from increasing.

(3) As described above, the active material layer of the negative electrode of the present invention has a high binder content at the current collector side interface, but has a high carbon content on the surface thereof, and thus is In this case, the entrance and exit of cations due to charge and discharge are not hindered, and there is no deterioration in performance due to the hindrance.

(4) Since the negative electrode of the present invention can reduce the overvoltage of the secondary battery using the negative electrode, it is possible to improve the discharge voltage and increase the capacity of the secondary battery.

(5) From the above, the negative electrode of the present invention can improve the cycle characteristics and self-discharge characteristics of a secondary battery, and can be made smaller and lighter, and can be used for small electronic devices, electric vehicles, and power storage. It provides a remarkably useful secondary battery as a power source for the above.

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

Example 1 The following two coating solutions were prepared using a powder of needle coke (KOA-SJ-Coke manufactured by Koa Oil Co., Ltd.) having an average particle size of 10 μm.

The coating liquid I was applied onto a 10 μ copper foil with a roll coater and dried to form a layer having a thickness of 12 μ. After that, the coating liquid II is applied and dried on the layer by a roll coater,
A negative electrode formed by forming a layer having a total film thickness of 175 μm was obtained. The active material of this negative electrode was firmly adhered to the current collector.

The contact resistance between the current collector of this negative electrode and the active material layer is 8 per cm ² .
It was 1 ohm.

Also, using this negative electrode, LiCoO ₂ , as a positive electrode, a propylene carbonate solution of 1.0 M-lithium perchlorate as an electrolytic solution, and a battery of 1.0 mA / cm ₂ of a 25 μm polyethylene microporous membrane assembled as a separator. The overvoltage at current density was 0.03 ohm.

Example 2 The same operation as in Example 1 was carried out except that carbon black (Raven410 manufactured by Columbia Carbon Co., Ltd.) was used instead of the needle coke of the coating solution I to form a layer having a thickness of 3 μ, and thereafter the same operation can be performed. Table 2 shows the evaluation results of the characteristics of the obtained negative electrode. This negative electrode was firmly attached to the current collector.

Example 3 A negative electrode obtained by performing the same operation after forming a layer having a film thickness of 2 μ using the coating liquid in which 100 parts by weight of needle coke of the coating liquid I in Example 1 was changed to 0 parts by weight. Table 2 shows the evaluation results of the characteristics of the above. This negative electrode was firmly attached to the current collector.

Example 4 A copper punching metal having a thickness of 50 μm was immersed in the coating liquid I of Example 1 to form a layer having an average film thickness of 13 μm. A mixture of 100 parts by weight of the needle coke powder used in Example 1 and 8 parts by weight of the polyethylene powder used in Example 1 was compression-formed thereon to obtain a negative electrode having a total film thickness of 350 μm.

Table 2 shows the characteristic evaluation results of this negative electrode. This negative electrode was firmly attached to the current collector.

Comparative Examples 1 and 2 A negative electrode was prepared by performing the same operation as in Example 1 and Example 4 without forming a film by the coating liquid I.

Table 2 shows the characteristic evaluation results of this negative electrode. Each of the negative electrodes had weak adhesion to the current collector, and the active material was easily peeled off.

Examples 5 to 8 and Comparative Examples 3 to 6 The coating liquid I and the coating liquid II used in Example 1 were changed to the compositions shown in Table 3, and after the coating liquid I and the coating liquid II were applied, respectively 120 The same operation as in Example 1 was carried out except that hot air drying was carried out at 0 ° C. Table 4 shows the contact resistance between the current collector and the active material of the obtained negative electrode and the overvoltage at 1.0 mA / cm ² of the battery prepared using this negative electrode.

Claims (1)

[Claims] 1. A negative electrode for a non-aqueous secondary battery comprising an active material layer formed of at least carbon as a negative electrode active material and a binder as constituent elements, and a current collector in contact with the active material layer.
The weight ratio of the binder to carbon at the interface of the portion of the active material layer that contacts the current collector is 0.2 to 9, and the weight ratio of the binder to carbon on the surface of the active material layer is 0.001 to
Non-aqueous secondary battery negative electrode characterized by being 0.15.