JPS6372065A - Nonaqueous solvent secondary battery - Google Patents

Abstract

PURPOSE:To obtain a battery having long charge-discharge cycle life and large discharge capacity by preparing a positive mix by bonding positive active material powder comprising chalcogen compound and conductive material powder with a binder having three dimensional net structure, and sticking the positive mix on a core to form a positive electrode. CONSTITUTION:Positive active material powder mainly comprising amorphous metal chalcogen compound is mixed with conductive material powder such as graphite. A fluorine resin binder, which forms a three dimensional net in molding process, such as polytetrafluoroethylene, chlorotrifluoroethylene, and tetrafluoroethylene-hexafluoroethylene copolymer is added to the mixture, and they are kneaded, then molded in a sheet by a roller to form a positive mix. The positive mix is sticked on a metal core to form a positive electrode 2. A negative active material 4 comprising lithium foil is placed on the positive electrode 2 through a separator 3. A negative can 5 is fitted to a positive can through an insulating gasket 6 to form a nonaqueous solvent secondary battery.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a non-aqueous solvent secondary battery equipped with an improved positive electrode, and more specifically, it has a long charge/discharge cycle life under heavy load and a low discharge capacity. The present invention relates to a nonaqueous solvent secondary battery that is large in size and therefore highly economical in use.

(Prior Art) In recent years, non-aqueous solvent secondary batteries using lithium as a negative electrode active material have been noted as batteries with high energy.

In these nonaqueous solvent secondary batteries, the positive electrode active materials combined with lithium include metal oxides, sulfides, and selenides, such as titanium, molybdenum, vanadium, zirconium, hafnium, tantalum, niobium, and chromium. Alternatively, tellurides, ie, metal chalcogen compounds, have been proposed.

Among these metal chalcogen compounds, vanadium pentoxide has useful electrical properties, and therefore lithium-based nonaqueous solvent secondary batteries using vanadium pentoxide as a positive electrode active material are being developed.

An example of such a secondary battery is shown in FIG. 2 as a longitudinal sectional view. In the figure, ■ is a positive electrode can made of a material such as stainless steel with nickel plating on the surface.
It also functions as a terminal board.

Inside this positive electrode can 1, a positive electrode 2 is arranged as shown in the figure.

This positive electrode 2 is a predetermined product in which a positive electrode mixture described below is integrally attached to one or both sides of a metal core made of nickel, stainless steel, etc., such as a wire mesh, punched metal, expanded metal, or foam metal. Manufactured by cutting or punching into shapes.

Here, the positive electrode mixture is composed of a metal chalcogen compound powder as described above and a conductive material powder such as graphite bound together with a binder such as polyethylene or polypropylene.

In this case, generally, metal chalcogen compound powder and conductive material powder are mixed in a predetermined ratio, a predetermined amount of binder is added to the resulting mixed powder, and the whole is sufficiently kneaded to obtain a kneaded product. It is made into foil by forming it into a plate or sheet.

A separator 3 is placed on the upper surface of the positive electrode 2 and is made of, for example, a polypropylene nonwoven fabric. This separator is impregnated with an electrolyte. For example, LiCI O4 + LiPF6, LiBF4,
Lithium salts such as Li0 or other commonly used electrolytes in lithium-based batteries such as NaCIO4, propylene carbonate, 1,2-dimethoxyethane.

Solutions with aprotic organic solvents such as γ-butyrolactone, dioxolane, ethylene carbonate, and 2-methyltetrahydrofuran alone or in combination are used.

4 is a lithium foil which is a negative electrode active material and is placed on the separator 3. , 5 is a negative electrode can which also serves as a negative electrode terminal plate, and is made of, for example, stainless steel with nickel plating applied to its surface.

Then, the negative electrode can 5 is connected to the positive electrode can 2 via the insulating backing 6.
A battery is formed by fitting the positive electrode can 2 into the positive electrode can 2 and bending the peripheral edge of the positive electrode can 2 inward to seal the whole.

(Problems to be Solved by the Invention) The following problems occur in secondary batteries using the above metal chalcogen compounds as positive electrode active materials.

One problem is that during discharge, the battery draws a discharge curve in which the potential changes in a stepwise manner, and the reversibility between charging and discharging is low, and particularly when the depth of discharge is deep, the charge/discharge cycle life is short. The second problem is that in the case of binders such as polyethylene and polypropylene mentioned above, the binders bond to each other while coating the particle surface of the active material powder or conductive material powder, resulting in the formation of a positive electrode mixture. Since binding ability is imparted, a large amount of binder is required to maintain proper binding ability, and as a result, not only the conductivity of the positive electrode mixture decreases but also the active material The problem is that the reaction area that contributes to battery reactions is also significantly reduced, resulting in lower electrochemical activity and lower discharge voltage.

The present invention aims to solve the above-mentioned problems and provide a novel non-aqueous solvent secondary battery that has a long charge/discharge cycle life under heavy load, has a low internal resistance, and has a large discharge capacity.

(Means for Solving the Problems) As a result of extensive research into positive electrodes by non-inventors in order to solve the above-mentioned problems, it has been found that excellent effects can be obtained when the positive electrode has the configuration described below. The inventors discovered that the battery of the present invention was developed.

That is, in the non-aqueous solvent secondary battery of the present invention, a positive electrode active material powder containing an amorphous metal chalcogen compound as a main component and a conductive material powder are held together by a fluororesin binder having a three-dimensional, network structure. The present invention is characterized in that it is equipped with a positive electrode formed by attaching a positive electrode mixture of 10% or more to a residual dust core.

The battery of the present invention is characterized by the positive electrode, especially the positive electrode mixture, and other elements are the same as the conventional battery shown in FIG. 2, so the following explanation will focus on the positive electrode, especially the positive electrode mixture. Proceed.

First, the main component of the positive electrode active material is a metal chalcogen compound powder as described above, and one with an amorphous structure is selected. Compared to crystalline metal chalcogen compounds, amorphous metal chalcogen compounds charge more reversibly when the battery is over-discharged to below its parking voltage, and have no over-discharge capacity. This is because it is excellent. Note that the term "amorphous" as used herein refers to a state in which, when the metal chalcogen compound of interest is identified by X-ray diffraction, the peak intensity that would appear in the case of a crystalline compound does not appear.

Such an amorphous totally bent chalcogen compound can be easily prepared by heating and melting a metal chalcogen compound of a predetermined composition, whether crystalline or amorphous, at a high temperature and then rapidly cooling the melt. can.

Next, the conductive material may be any conventionally used material, such as graphite powder and carbon black.

Further, the binder is a fluororesin that can be deformed into a three-dimensional network shape during molding of the positive electrode mixture, which will be described later. Specifically, when shear stress is applied, fluorine-based resins that turn into fibers and become three-dimensionally intertwined, such as polytetrafluoroethylene,
Suitable examples include chlorotrifluoroethylene and tetrafluoroethylene-hexanefluoropropylene copolymer.

The positive electrode mixture according to the present invention can be manufactured as follows.

First, amorphous metal chalcogen compound powder and conductive material powder are mixed in a predetermined ratio. These powders usually have an average particle size of 3 to 90 microns.

The mixing ratio of the two is preferably set to 98 to 70 parts by weight for the former and 2 to 30 parts by weight for the latter.

Next, the above-mentioned fluororesin binder is added to this mixed powder and kneaded. The amount added is preferably 3 to 10 parts by weight of the fluororesin per 100 parts by weight of the mixed powder. This is because if too much is added, the conductivity of the mixture obtained will decrease, and if too little is added, no binding ability will be imparted.

The mixed powder and the binder are preferably kneaded using a ball mill, an automatic mortar mixer, a screw conveyor, or the like, since shear stress can be preliminarily applied to the binder.

The obtained kneaded product is then subjected to, for example, multiple roll forming operations to form a plate or sheet. During this molding process, the binder is subjected to strong shearing stress and becomes fiberized, and these fibers become entangled in a network to form a three-dimensional network structure. At the same time, the powder of the positive electrode active material and the powder of the conductive material are not coated on their entire surface with the binder, but some of their surfaces are bound to the binder and inside the network structure of the binder. He is in a state of strict restraint.

That is, each powder of the positive electrode active material and the conductive material is taken into the network structure of the binder and held in a restrained state. Therefore, the binding ability of the entire mixture is maintained at a high level even though the amount of binder is smaller than in the case where the entire surface is coated with each powder. Moreover, the reaction area of the active material powder that contributes to the battery reaction remains large.

The positive electrode according to the present invention can be obtained by attaching the sheet or plate of the positive electrode mixture thus obtained to a metal core in the conventional manner.

After that, if this positive electrode is assembled into a battery in the same way as before,
A non-aqueous solvent secondary battery of the present invention is obtained.

(Embodiment of the invention) Example Vanadium pentoxide and tungsten trichloride in a molar ratio of 9
Mix so that 5=5, and heat this mixture for 1500'
After melting at C for 8 hours, it was rapidly cooled in dry air at a cooling rate of lXl0'°C/sec to obtain V205-5 mol%.
A metal chalcogen compound called WO3 was prepared by A. When it was identified by X-ray diffraction, it was found to have an amorphous structure.

After thoroughly mixing 75 parts of this active material powder (average particle size 70 μm), 25 parts by weight of acetylene black, and 5 parts by weight of polytetrafluoroethylene powder in a ball mill, the resulting mixture was heated to the extent that a person could put their weight on it. Roll forming was repeated 8 times while applying shear stress to a thickness of 0.4 m.
I made it into a sheet of m.

One side of this sheet was crimped to a 60-mesh stainless steel wire gauze, then punched to a thickness of 0.5 m + o.
A positive electrode with a diameter of 0.51111 mm was obtained.

A button-type non-aqueous solvent secondary battery having the structure shown in FIG. 2 was manufactured by incorporating this positive electrode, and this was used as an example battery. The negative electrode is lithium foil, and the electrolyte is propylene carbonate.
iO4 was dissolved at a concentration of 1 mol/liter, and the separator was a polypropylene nonwoven fabric.

For comparison, a battery having the same structure as the Example battery except that the positive electrode active material was crystalline V2O5-5 mol % WO3 was manufactured, and this was designated as Comparative Example 1 battery.

In addition, a battery having the same structure as the example battery except that the binder was polyethylene was manufactured, and this was used as a comparative example. It was used as a battery.

For these three types of batteries, one cycle consisted of discharging from 3V to 2V under a constant load of LOKΩ and then charging to 3V again, and a charge/discharge cycle characteristic evaluation test was conducted to examine the capacity change for each cycle. I performed a funeral. The results are shown in FIG. 1 as a characteristic diagram. In FIG. 1, the horizontal axis represents the number of cycles, and the vertical axis represents the discharge capacity deterioration rate (%) relative to the initial capacity in each cycle. As is clear from the figure, the battery of the present invention has a larger discharge capacity than the battery of the comparative example, and has a significantly improved charge/discharge cycle life, especially under heavy loads.

(Effects of the Invention) As is clear from the above explanation, the non-aqueous solvent secondary battery of the present invention has a shorter charge-discharge cycle life due to inactivation of the positive electrode active material that occurs as the depth of discharge becomes deeper. In order to prevent short life, the entire surface of the active material powder is not coated with a binder, so the discharge reaction area of the active material is also large, and the active material and electrolyte are compatible with each other. The discharge characteristics have been improved. Furthermore, the mechanical strength of the entire positive electrode is sufficient even though the amount of binder used is significantly reduced compared to the conventional method. Furthermore, since the amount of binder used is small, the electrical resistance of the positive electrode is also reduced, and the discharge characteristics of the battery are improved.

As described above, the battery of the present invention has excellent properties, the positive electrode is easy to manufacture, and is suitable for mass production, so it has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the number of charge/discharge cycles of a battery and the discharge capacity deterioration rate, and FIG. 2 is a longitudinal cross-sectional view of a button-type nonaqueous solvent secondary battery. 1-Positive electrode can 2-Positive electrode 3-Separator 4-Negative electrode
5- Negative electrode can 6- Insulating backing Figure 2

Claims (1)

[Scope of Claims] 1. A positive electrode mixture in which a positive electrode active material powder mainly composed of an amorphous metal chalcogen compound and a conductive powder are held together by a fluororesin binder with a three-dimensional network structure is A non-aqueous solvent secondary battery comprising a positive electrode attached to a core. 2. The fluororesin binder is any one of polytetrafluoroethylene, chlorotrifluoroethylene, or tetrafluoroethylene-hexafluoroethylene copolymer
The non-aqueous solvent battery according to claim 1, which is a seed.