JPH0864232A - Manufacture of nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE: To provide a nonaqueous electrolyte secondary battery having a high cycle life characteristic by using a required resin as the binder of a battery active material to assemble the battery, then heat-treating it. CONSTITUTION: A vinyl fluoride resin or a vinylidene fluoride resin is used as the binder of a battery active material to assemble a nonaqueous electrolyte secondary battery. The battery is left at the temperature of 40-60 deg.C for 5hr in the opened state, then it is left at the room temperature for 12hr for heat treatment. Part of the vinylidene fluoride resin or vinyl fluoride resin is dissolved in an electrolyte, it is gelatinized when it is returned to the room temperature, and it is not dissolved in the electrolyte when it is again heated. The small, lightweight nonaqueous electrolyte secondary battery capable of holding battery characteristics including a high cycle life characteristic, a high energy density, and a high output over a long period is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries are superior to water-based electrolyte secondary batteries in terms of high energy density, small size and light weight, but have drawbacks in output characteristics. This is because the ionic conductivity of the non-aqueous electrolytic solution is generally lower by one to two orders of magnitude than that of the aqueous electrolytic solution. Therefore, a method of solving this problem and improving the output characteristics by using a thin film and a large-area electrode is performed.

Conventionally, as a method of molding an electrode of a non-aqueous electrolyte secondary battery, an electrode active material is dispersed in an organic solvent solution in which a butadiene rubber resin is dissolved as a binder, and then coating and drying are performed. It was being done. According to this method, a thin film and a large-area electrode can be easily obtained, but on the other hand, the influence of the binder, which is an insulating material, on the electrode active material is significantly large. It was not practical because the rise in the value was seen.

In order to solve such a problem, it has been proposed to use a fluorine-based polymer material such as vinyl fluoride resin or vinylidene fluoride resin, which acts as an ionic conductor, as a binder.

[0005]

However, since the fluoropolymer vinyl fluoride resin and vinylidene fluoride resin, which are the fluoropolymers, are partially dissolved in the electrolytic solution using a polar solvent, after being assembled into a battery, the binder is not used. There is a drawback that the components move into the electrolytic solution, the active material falls off from the electrode, and the life characteristics deteriorate. In particular, in an active material that utilizes a lithium ion intercalation-deintercalation reaction, there is expansion and contraction associated with the reaction, and thus the active material was easily removed. Further, at high temperatures, the dissolution of the binder component was accelerated, and the active material was also dropped off.

Therefore, an object of the present invention is to improve cycle life characteristics, which results in high energy density, small size and light weight,
It is an object of the present invention to provide a method for producing a non-aqueous electrolyte secondary battery that can maintain high-output battery performance for a long period of time.

[0007]

In order to achieve the above object, the method for producing a non-aqueous electrolyte secondary battery of the present invention uses a vinyl fluoride resin or vinylidene fluoride resin as a binder of a battery active material. In manufacturing the water electrolyte secondary battery, the battery is heat-treated after the battery is assembled.

Further, the heat treatment of the battery is characterized in that the battery is left in an open circuit state at a temperature of 40 to 60 ° C. and then left in an open circuit state at room temperature.

Further, the heat treatment of the battery is performed at a temperature of 40-60.
It is characterized in that it is charged / discharged at a rated current of 0.5 C or less at 0 ° C. and then left at room temperature in an open circuit state.

[0010]

[Function] The vinyl fluoride resin and vinylidene fluoride resin are partially dissolved when heated to 40 to 60 ° C. in a state where they are in contact with the electrolytic solution in the battery, but when they are returned to room temperature, they are gelled and again
It is no longer dissolved in the electrolytic solution even when heated to 0 ° C or higher.

Therefore, after the battery is assembled, the heat treatment described above prevents the binder from being redissolved in the electrolytic solution in the battery and the active material from falling off from the electrode.

Further, the same effect can be obtained by heat treatment while charging / discharging at a rated current of 0.5 C or less.

[0013]

EXAMPLES Examples of the method for producing a non-aqueous electrolyte secondary battery of the present invention will be described below.

(Example 1) First, LiCoO ₂ powder 10
7 parts by weight of acetylene black was mixed with 0 parts by weight, 100 parts by weight of a dimethylformamide solution of vinylidene fluoride resin (concentration 4 wt%) was added as a binder, and the mixture was stirred to prepare a coating liquid. Then, using aluminum foil (thickness 30 μm) as a base material, this coating solution is applied to both surfaces of the aluminum foil and dried,
The positive electrode had a thickness of 0.18 mm, a width of 40 mm, and a length of 260 mm.

Next, 100 parts by weight of a dimethylformamide solution of vinylidene fluoride resin (concentration 5 wt%) was added to 100 parts by weight of natural graphite produced in Madagascar, and mixed and stirred to obtain a coating liquid. Then, using a copper foil (thickness 20 μm) as a base material, this coating solution is applied and dried to have a thickness of 0.18 mm,
The negative electrode had a width of 40 mm and a length of 280 mm. Further, a battery having a rated value of 500 mAh was assembled by using a solution obtained by dissolving LiClO ₄ in a propylene carbonate solution at a concentration of 1 mol.

FIG. 1 is a partial cross-sectional view of the cylindrical battery assembled in this embodiment. In the figure, 1 is a non-aqueous organic electrolyte resistant battery case made by processing a stainless steel plate, 2 is a sealing plate provided with a safety valve, and 3 is an insulating packing. Reference numeral 4 denotes an electrode plate group, in which the positive electrode 4a and the negative electrode 4b are spirally wound a plurality of times via the separator 4c and are housed in the case 1. The positive electrode lead 5 is drawn out from the positive electrode 4a and connected to the sealing plate 2, and the negative electrode 4b
A negative electrode lead 6 is drawn out from the above and is connected to the bottom of the battery case 1. Further, 7 is an insulating ring provided on the upper and lower portions of the electrode plate group 4, respectively.

After the battery was assembled in this manner, it was left in an open circuit state at 60 ° C. for 5 hours for heat treatment, and then left at room temperature for 12 hours. Then, charge / discharge current 500
A constant current charge / discharge test was performed under the conditions of mA, end-of-charge voltage 4.1V, and end-of-discharge voltage 3.0V.

(Example 2) After assembling a battery in the same manner as in Example 1, the charging / discharging current was 250 mA at 60 ° C (that is, a current having a rating of 0.5 C), the charge end voltage was 4.1 V, and the discharge end voltage was 3. The battery was charged and discharged for 5 cycles under the condition of 0.0 V and then left at room temperature for 12 hours in an open circuit. Then Example 1
A constant current charge / discharge test was carried out under the same conditions as above.

Comparative Example 1 A battery was assembled in the same manner as in Example 1. Then, a constant current charge / discharge test was performed under the same conditions as in Example 1 without performing heat treatment.

(Comparative Example 2) After assembling a battery in the same manner as in Example 1, a charge / discharge current of 500 mA (that is, a current of rated 1C) at 60 ° C, a charge end voltage of 4.1V, and a discharge end voltage of 3.0V. The battery was charged and discharged for 5 cycles under the above conditions, and then left at room temperature for 12 hours in an open circuit. Thereafter, a constant current charge / discharge test was conducted under the same conditions as in Example 1.

Table 1 shows the initial capacity before the constant current charge / discharge test and the capacity at the 200th cycle of the constant current charge / discharge test for Example 1, Example 2, Comparative Example 1 and Comparative Example 2.
In addition, a charge / discharge test was performed under the same conditions for the above-mentioned four different types of batteries, the test was stopped at the time of charging at the 50th cycle, the batteries were disassembled, and the internal electrodes were observed. The results are also shown in Table 1.

[0022]

[Table 1]

The symbols in the electrode state column of the decomposition battery in Table 1 indicate the following states, respectively. ○ indicates
No significant changes such as swelling or falling of the active material layer were observed. The symbol Δ indicates that the electrode state was maintained although the active material layer partially swelled and fell off. The symbol X indicates that the active material layer was swelled and dropped, and the electrode did not maintain its original state.

As shown in Example 1 of Table 1, the heat-treated product of the present invention had a large initial capacity, and the capacity after the charge-discharge cycle test hardly decreased, and no noticeable change was observed in the electrode. Excellent charge / discharge cycle characteristics.
On the other hand, in the case where the heat treatment was not performed, Comparative Example 1
As shown in, the initial capacity is slightly lower than that of the heat-treated one, but the capacity after the charge / discharge test is significantly reduced, and the electrode is deteriorated by swelling, falling off of the active material layer. There is.

Also, as shown in Example 2, there was almost no decrease in the capacity after the charge / discharge cycle test, and no noticeable change was observed in the electrode, even when heat-treated while being charged / discharged at a rated current of 0.5C. Excellent charge / discharge cycle characteristics. On the other hand, in the case of heat treatment while charging / discharging at a current exceeding 0.5 C as rated, as shown in Comparative Example 2, the capacity after the charging / discharging test was significantly reduced, and the active material layer of the electrode swelled,
It has fallen off and deteriorated.

Although propylene carbonate is used as the solvent of the electrolytic solution in the above embodiment, the solvent is not limited to this. That is, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, esters, carbonates, nitro compounds, sulfolane compounds and the like generally used for non-aqueous electrolyte batteries can be appropriately used. .

Although vinylidene fluoride resin (--CH ₂ --CF _2- ) _n is used as the binder of the battery active material, vinyl fluoride resin (--CH ₂ --CHF--) _n is also used. The effect is obtained. Furthermore, -CF (CF _{3)
-CF 2 -, - CF 2 -CF} 2 -, - CH (CH 3) -
A fluoropolymer copolymer containing a monomer unit represented by CH ₂ — can also be appropriately used.

Further, in the above-mentioned embodiment, the heat treatment after assembling the battery is carried out at 60 ° C. for 5 hours, but the present invention is not limited to this condition.
That is, the temperature is preferably in the range of 40 to 60 ° C. This is because the gelling reaction of the binder hardly progresses below 40 ° C., and on the other hand, when it exceeds 60 ° C., other battery constituent components may have an adverse effect such as thermal deterioration. Also, the time is 5 to 48 hours, and especially 5 to 12 hours.
Time is preferred. This is because the gelling reaction of the binder does not proceed sufficiently in less than 5 hours, while the gelling reaction begins to saturate in more than 12 hours, and further gelation reaction hardly occurs in more than 48 hours.

[0029]

As is apparent from the above description, according to the method for producing a non-aqueous electrolyte secondary battery of the present invention, an electrode using a vinyl fluoride resin or vinylidene fluoride resin as a binder is assembled in a battery. According to the present invention, after heat treatment,
The charge / discharge cycle characteristics of the non-aqueous electrolyte secondary battery are improved, and high energy density, small size and light weight, and high output battery performance can be maintained for a long period of time.

The same effect can be obtained by heat treatment while charging / discharging at a rated current of 0.5 C or less.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a battery obtained according to an embodiment of the present invention.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Insulating Packing 4 Electrode Plate Group 4a Positive Electrode 4b Negative Electrode 4c Separator 5 Positive Electrode Lead 6 Negative Lead 7 Insulating Ring

Claims (3)

[Claims] 1. A method for producing a non-aqueous electrolyte secondary battery using a vinyl fluoride resin or a vinylidene fluoride resin as a binder of a battery active material, wherein the battery is assembled and then heat treated. Manufacturing method of non-aqueous electrolyte secondary battery. 2. The heat treatment of a battery is carried out at a temperature of 40 at an open circuit state.
The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the method is left in a temperature range of -60 ° C and then left in an open circuit state at room temperature. 3. The heat treatment of the battery is performed by charging / discharging at a temperature of 40 to 60 ° C. at a rated current of 0.5 C or less, and then leaving the battery at room temperature in an open circuit state. Manufacturing method of non-aqueous electrolyte secondary battery.