JPH09129264A - Manufacture of nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the deterioration of the charge and discharge cycle characteristic of a cell after aging, regarding a nonaqueous electrolyte secondary battery. SOLUTION: A power generation element formed out of a negative electrode using a carbon material as a negative electrode active material, a positive electrode and a separator, is sealed into a battery jar, together with a nonaqueous electrolyte, to assemble a cell. The cell is, then, initially charged up to the prescribed voltage V1 and initially discharged to the prescribed voltage V2. Thereafter, the cell is subjected to an aging process during the prescribed period (e.g. one month) and finally charged up to the prescribed voltage V4. As a result, the cell comes to be aged in the condition where the voltage of the cell is lowered, due to the initial discharge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a non-aqueous electrolyte secondary battery that exhibits good charge / discharge cycle characteristics after aging.

[0002]

2. Description of the Related Art FIG. 4 is a graph showing a voltage curve in a conventional method for manufacturing a non-aqueous electrolyte secondary battery.

Conventionally, when manufacturing a non-aqueous electrolyte secondary battery, after assembling the unit cells, as shown in FIG. 4, after initial charging to a predetermined voltage V1, it takes about one month at room temperature. Aging was performed, and the unit cell whose voltage had dropped to V3 due to aging was charged to a predetermined voltage V4 before shipment.

[0004]

However, in this case, since the aging is performed in a state where the unit cell is almost fully charged, there is a disadvantage that the charge / discharge cycle characteristics of the unit cell after aging are deteriorated.

In view of the above circumstances, it is an object of the present invention to provide a method for manufacturing a non-aqueous electrolyte secondary battery which can suppress deterioration of charge / discharge cycle characteristics after aging.

[0006]

That is, a method of manufacturing a non-aqueous electrolyte secondary battery according to the present invention is directed to a battery can including a non-aqueous electrolyte and a power-generating element including a negative electrode having a carbon material as a negative electrode active material, a positive electrode and a separator. Assemble the unit cell by enclosing it inside, then perform the initial charge of this unit cell, then perform the initial discharge of this unit cell, then perform the aging of this unit cell, and finally, It is configured to be charged to a predetermined voltage.

The cutoff voltage of the initial charge of the unit cell is 4.2 V, and the cutoff voltage of the initial discharge of the unit cell is 3.
Configured as 0-3.8V.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a graph showing a voltage curve in the method for producing a non-aqueous electrolyte secondary battery according to the present invention.

The manufacturing method of the non-aqueous electrolyte secondary battery according to the present invention is performed in the following procedure.

First, a unit cell is assembled by encapsulating a power generating element consisting of a negative electrode using a carbon material as a negative electrode active material, a positive electrode and a separator together with a non-aqueous electrolyte in a battery can.

When the unit cell is assembled in this manner, initial charging, initial discharge, aging and charging are sequentially performed on the unit cell as shown in FIG. That is, the unit cell is initially charged to a predetermined voltage V1 and then initially discharged to a predetermined voltage V2. After that, aging is performed for a predetermined period. Then, since the voltage of the unit cell drops to the voltage V3, the unit cell is charged to the predetermined voltage V4.

As described above, since the voltage of the unit cell is lowered to the predetermined voltage V2 when aging is performed, compared with the case where the aging is performed in a state in which the unit cell is close to full charge, the aging after the aging is performed. The deterioration of the charge / discharge cycle characteristics of the unit cell is suppressed.

[0013]

Embodiments of the present invention will be described below. FIG. 2 is a graph showing the charge / discharge cycle characteristics of the non-aqueous electrolyte secondary battery, and FIG. 3 is a graph showing the relationship between the final voltage before aging and the discharge capacity after 100 cycles.

Assembly of Unit Cell A positive electrode sheet was prepared as follows. That is, 90.5 parts by weight of LiCoO ₂ powder as a positive electrode active material, 4.5 parts by weight of graphite as a conductive agent, and 5 parts by weight of polyvinylidene fluoride as a binder were mixed, and n-methylpyrrolidone was added thereto. A positive electrode slurry was prepared by adding it as a dispersant. The positive electrode slurry was uniformly applied to both surfaces of an aluminum foil current collector having a thickness of 20 μm, dried, and then roller pressed to obtain a positive electrode sheet. Further, an aluminum positive electrode lead plate was attached to the end of this positive electrode sheet by welding.

The negative electrode sheet was manufactured as follows. That is, 90 parts by weight of glassy carbon as the negative electrode active material,
Polyvinylidene fluoride 10 was mixed as a binder, and n-methylpyrrolidone was added as a dispersant to the mixture to prepare a negative electrode slurry. This negative electrode slurry has a thickness of 10 μm
The copper foil current collector was evenly coated on both sides and dried, and then roller pressed to obtain a negative electrode sheet. Further, a nickel negative electrode lead plate was attached to the end of this negative electrode sheet by welding.

The positive electrode sheet and the negative electrode sheet were laminated with a polyethylene separator interposed therebetween and spirally wound to obtain a power generating element. After accommodating the power generating element in the battery can, the positive electrode lead plate and the negative electrode lead plate were welded to the sealing portion and the battery can, respectively. Further, a non-aqueous electrolytic solution was injected, the sealing portion was fitted into the opening of the battery can, and caulking and sealing were performed to assemble a cylindrical unit cell having an outer diameter of 14.3 mm and a height of 50.5 mm. .

Charge / Discharge Cycle Test The unit cells assembled as described above were subjected to constant current charging at a charging current of 400 mA and a final voltage of 4.2 V, and then a constant current discharge up to a discharge current of 400 mA and a final voltage of 3.5 V. After that, it was aged for 1 month (method according to the invention).

On the other hand, the unit cells assembled as described above were subjected to constant current charging at a charging current of 400 mA and a final voltage of 4.2 V, and then immediately (that is, without discharging) for one month. (Conventional method).

After aging, a constant current charge / discharge cycle was performed 200 times at a current of 400 mA, a charge end voltage of 4.2 V, and a discharge end voltage of 2.8 V.

The relationship between the number of cycles and the discharge capacity is shown in FIG. As is apparent from FIG. 2, the method according to the present invention is superior in charge / discharge cycle characteristics as compared with the conventional method.

Further, in order to investigate the influence of the final voltage before aging on the charge / discharge cycle characteristics after aging, the relationship between the final voltage before aging and the discharge capacity after 100 cycles was obtained. The result is shown in FIG.

As is clear from FIG. 3, in the case of the conventional method (when the final voltage before aging is 4.2 V), the discharge capacity after 100 cycles was about 300 mAH, whereas in the case of before aging. Final voltage of 2.8-3.8V
In this case, the discharge capacity after 100 cycles is about 360
Since it is above mAH, the charge / discharge cycle characteristics after aging are significantly improved.

Further, in order to investigate the influence of the cut-off voltage before aging on the detection capability of the internal short-circuited product after aging, an internal short-circuited product with a 0.5 mm square hole intentionally opened in the separator was assembled and aged for 30 days. Then, it was investigated whether it could be detected as a defective product. Whether or not the open circuit voltage of the battery has reached the reference open circuit voltage (see Table 1 for specific numerical values) and whether the internal resistance of the battery is within the standard internal resistance range (see Table 1 for specific numerical values) Or not. Table 1 shows the results.

[0024]

[Table 1]

As is clear from Table 1, when the final voltage before aging was 3.0 V or more, the detection capability of the internal short-circuited product after aging was 100%, whereas the final voltage before aging was terminated. When the voltage was 2.8 V, the detectability of the internal short-circuited product after aging decreased to 98%.

Therefore, the final voltage before aging (that is,
When the final discharge end voltage) is 3.0 to 3.8 V, deterioration of charge-discharge cycle characteristics can be significantly suppressed without causing a situation in which the detection capability of the internal short-circuited product is deteriorated after aging. it can.

[0027]

As described above, according to the present invention, a power generating element consisting of a negative electrode having a carbon material as a negative electrode active material, a positive electrode and a separator is enclosed in a battery can together with a non-aqueous electrolyte to assemble a unit cell. Then, the initial charging of the unit cell is performed, then the initial discharging of the unit cell is performed, then the aging of the unit cell is performed, and finally the unit cell is charged to a predetermined voltage. Because I did
In addition to being able to confirm the discharge capacity by charging and discharging the unit cell before aging, since the aging is performed with the unit cell voltage dropping due to the initial discharge, charging and discharging of the unit cell after aging It is possible to provide a method for manufacturing a non-aqueous electrolyte secondary battery capable of suppressing deterioration of cycle characteristics.

The cutoff voltage of the initial charge of the unit cell is 4.2 V, and the cutoff voltage of the initial discharge of the unit cell is 3.
When configured as 0 to 3.8 V, the effect of suppressing the deterioration of the charge and discharge cycle characteristics described above becomes remarkable, and at the same time, it becomes possible to avoid a situation in which the ability to detect an internal short-circuited product after aging decreases.

[Brief description of the drawings]

FIG. 1 is a graph showing a voltage curve in a method for manufacturing a non-aqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a graph showing charge / discharge cycle characteristics of a non-aqueous electrolyte secondary battery.

FIG. 3 is a graph showing the relationship between the final voltage before aging and the discharge capacity after 100 cycles.

FIG. 4 is a graph showing a voltage curve in a conventional method for manufacturing a non-aqueous electrolyte secondary battery.

Front page continuation (72) Inventor Masatake Nishio 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd.

Claims (2)

[Claims] 1. A unit cell is assembled by encapsulating a power generation element including a negative electrode using a carbon material as a negative electrode active material, a positive electrode and a separator in a battery can together with a non-aqueous electrolyte, and then performing initial charging of the unit cell. After that, the initial discharge of the unit cell is performed, then the aging of the unit cell is performed, and finally, the method for manufacturing a non-aqueous electrolyte secondary battery configured to charge the unit cell to a predetermined voltage . 2. The final voltage of the initial charge of the unit cell is 4.2 V
And the final voltage of the initial discharge of the unit cell is 3.0 to 3.8V.
The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein