JP2000090974A - Lithium ion secondary battery and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To provide a lithium ion secondary battery for improving battery performance and stabilizing quality and a method for manufacturing the same. SOLUTION: A power generation element and an electrolytic solution are accommodated in a battery case, and before the opening end of the battery case is sealed, after the pre-charge or during the pre-charge, a decompression process is performed, and then the battery case is sealed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium ion secondary battery and a method for manufacturing the same.

[0002]

2. Description of the Related Art A general structure of a lithium ion secondary battery is shown in FIG. In this lithium ion secondary battery, an electrode group 3 in which a positive electrode plate and a negative electrode plate are formed in a wound structure with a separator interposed therebetween in a battery case 1 and an electrolyte are accommodated, and a positive electrode lead pulled out from the positive electrode plate Sealing lid 2 connected to 4
Thus, the opening of the battery case 1 is sealed.

[0003] The lithium ion secondary battery formed as described above is used in a finishing process in its manufacturing process to extract defective batteries and prevent elution of metal materials such as a core of an electrode plate and a battery case. A pre-charging process is performed in which a charging power supply is connected and charging is performed.

[0004]

However, in the case of a lithium ion secondary battery using a carbon material, particularly a graphite material for the negative electrode, a gas generation reaction occurs at the time of preliminary charging, which is the first charging. The gas stays between the electrode plates to hinder the charge / discharge reaction of the battery, and the battery capacity and the dispersion of the battery capacity are increased, resulting in a problem that the reliability of the battery is reduced.

An object of the present invention is to provide a highly reliable lithium ion secondary battery which eliminates the adverse effects of pre-charging and a method of manufacturing the same.

[0006]

In order to achieve the above object, a lithium ion secondary battery according to the present invention has a structure in which a positive electrode plate and a negative electrode plate are formed in a battery case in a wound structure with a separator interposed therebetween. Before closing the opening of the battery case, the battery pack is connected to a charging power source to perform pre-charging, and the pre-charging or after the pre-charging is performed under a reduced pressure at a predetermined pressure before the battery is closed. It is characterized in that the opening of the case is sealed.

[0007] According to the above configuration, pre-charging and decompression are performed before the opening of the battery case is sealed. Therefore, even if gas generated by pre-charging stays between the electrode plates, the inside of the battery case is depressurized by decompression. From the outside through the opening. Since the opening is sealed after the gas is removed from the inside of the battery case as described above, the adverse effect of the gas remaining between the electrodes to cause a reduction in the battery capacity or a variation in the battery capacity is suppressed, and a high-quality and stable battery is suppressed. A high performance lithium ion secondary battery can be provided.

[0008] In a first method of manufacturing a lithium ion secondary battery according to the present invention for achieving the above object, a positive electrode plate and a negative electrode plate are interposed between an open end of a battery case and a battery case through a separator. A pre-charging step is carried out before the step of housing the electrode group formed in a wound structure and injecting the electrolyte and closing the opening end of the battery case, and after this pre-charging, depressurizing at a predetermined pressure After performing the step of performing, the battery case is manufactured by a step procedure of sealing the open end of the battery case.

According to this manufacturing method, the pre-charging is performed before the opening of the battery case is sealed, and even if the gas generated by the pre-charging stays between the electrode plates, the decompression process is performed thereafter. As a result, it is discharged from the battery case to the outside through the opening. Since the opening is sealed after the gas is removed from the inside of the battery case as described above, the adverse effect of the gas remaining between the electrodes to cause a reduction in the battery capacity or a variation in the battery capacity is suppressed, and a high-quality and stable battery is suppressed. A high performance lithium ion secondary battery can be manufactured.

A second method for manufacturing a lithium ion secondary battery according to the present invention for achieving the above object is characterized in that a positive electrode plate and a negative electrode plate are inserted from the open end of the battery case into the battery case via a separator. Before the step of housing the electrode group formed into a wound structure and injecting the electrolyte and closing the opening end of the battery case, a step of performing a pre-charge while performing a pressure reduction treatment at a predetermined pressure was performed. Thereafter, the battery case is manufactured by a process procedure of closing an open end of the battery case.

In this manufacturing method, since the pre-charging is performed under a reduced pressure, the gas generated by the pre-charging is released from the inside of the battery case to the outside through the opening by the decompression, so that the gas is discharged between the electrode plates. No stagnation.
Since the opening is sealed after the gas is removed from the inside of the battery case as described above, the adverse effect of the gas remaining between the electrodes to cause a reduction in the battery capacity or a variation in the battery capacity is suppressed, and a high-quality and stable battery is suppressed. A high performance lithium ion secondary battery can be manufactured.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention.
The embodiment described below is an example embodying the present invention, and does not limit the technical scope of the present invention.

FIG. 1 shows a configuration of a lithium ion secondary battery, in which a positive electrode plate and a negative electrode plate are wound via a separator in a battery case 1 in which a stainless steel plate is formed in a bottomed cylindrical shape. The battery case 1 containing the element 3 and the electrolyte
Is closed by a sealing lid 2.

The positive electrode plate is made of LiCoO ₂ powder, acetylene black, and a fluororesin-based binder in a ratio of 100: 3: 7.
Are mixed at a ratio, and the positive electrode mixture suspended in a carboxymethylcellulose aqueous solution and formed into a paste is applied to both sides of a current collector formed of aluminum foil, and is formed into a predetermined shape by drying, rolling, and cutting. . The negative electrode plate was prepared by mixing mesophase small sphere particles obtained by graphitizing mesophase small sphere powder at a high temperature and styrene / butadiene rubber at a ratio of 100: 5, and suspending the mixture in carboxymethylcellulose aqueous solution to form a paste. An agent is applied to both sides of a current collector formed of copper foil, and dried, rolled, and cut into a predetermined shape. The positive electrode plate and the negative electrode plate are formed in a wound electrode group 3 via a separator formed of a polyethylene porous film.

FIG. 2 shows the first and second embodiments of the method of manufacturing the lithium ion secondary battery having the above-described structure, which are performed by changing the procedure of the decompression process which is a characteristic process of the present invention. This will be described below. .. Shown in FIG. 2 are step numbers indicating the process procedures, and correspond to the numbers added to the text.

[First Embodiment] In FIG. 2A,
The electrode plate group 3 is housed in the battery case 1 (S1), and the leads of the negative electrode plate are spot-welded to the battery case 1 for electrical conduction, so that the battery case 1 constitutes a negative electrode output terminal of the battery. . Further, the positive electrode lead 4 pulled out from the positive electrode plate is connected to the sealing lid 2, and the sealing lid 2 forms a positive output terminal of the battery (S2). The non-aqueous electrolyte is injected into the battery case 1 in which the power generation element 3 is stored (S3).

Next, the pre-charging is performed by setting the environmental temperature to 20 ° C. (S4). The pre-charging is performed by connecting the plus of the charging power source to the sealing lid 2 and the minus of the battery case 1 held in a state where the opening end of the battery case 1 is not sealed, and charging for 1 hour with a constant current of 200 mA. Do.

After the completion of the preliminary charging, 300 mmHg
For one minute (S5).

After the completion of the precharging and the pressure reduction, the opening end of the battery case 1 is sealed with the sealing lid 2 to complete a lithium ion secondary battery (S6).

[Second Embodiment] In FIG. 2B,
The process procedure of steps S11 to S13 is the same as that of the first embodiment.
Same as 1 to S3. In the next step, 300mm
Preliminary charging is performed under Hg pressure reduction processing (S14).

After the completion of the precharging and the pressure reduction, the opening end of the battery case 1 is sealed with the sealing lid 2 to complete the lithium ion secondary battery (S15).

In order to verify the improvement of the battery performance of the lithium ion secondary battery manufactured by performing the decompression process according to each of the first and second embodiments, the conventional device manufactured without performing the decompression process is used. Performance comparison was performed with the lithium ion secondary battery of the example.

The conventional lithium ion secondary battery has the same battery construction and steps up to precharging, and has a constant current of 200 mA at an ambient temperature of 20 ° C. as in the case of the first embodiment. For 1 hour, and the opening end of the battery case 1 is sealed by the sealing lid 2 after the completion of the preliminary charging.

Each of the lithium ion secondary batteries manufactured by the first and second embodiments and the method of the prior art is prepared in a quantity of 1000 cells, and a charge / discharge test is performed on these cells. The charging conditions for the charge / discharge test were as follows: at an ambient temperature of 20 ° C., constant current charging was performed by a constant current control with a charging current value of 700 mA until the battery voltage reached 4.1 V, and then a constant voltage control of 4.1 V was performed. Charge at constant voltage until the charging time reaches 2 hours. The discharge condition is a discharge current value 2
A constant current discharge of 00 mA is performed until the battery voltage reaches 3.0 V.

FIG. 3 is a frequency distribution diagram showing the discharge capacity of each battery calculated from the discharge current value and the discharge duration in the charge / discharge test. FIG. 4 similarly shows the internal resistance of each battery as a frequency distribution diagram. The mark “*” indicates that 20 cells are present, and the number of batteries whose discharge capacity (mAh) or internal resistance (mΩ) shown on the vertical axis is measured is plotted. , Example 1 and Example 2 each 1
The distribution of 000 cells is shown.

As can be seen from FIGS. 3 and 4, the lithium ion secondary battery manufactured by the conventional manufacturing method is as follows.
Both the discharge capacity and the internal resistance have a wide distribution range, and it is difficult to obtain constant battery performance. On the other hand, the lithium ion secondary batteries manufactured by the manufacturing methods of the first and second embodiments have a small variation in both discharge capacity and internal resistance. Further, even if the average value of the discharge capacity and the internal resistance is calculated, there is a large difference between the conventional example and the first and second examples. The ion secondary battery has realized high-order stabilization. In the comparison between the first embodiment and the second embodiment 2, there is no significant difference in the frequency distribution and the average value.

After the charge / discharge test was performed, each battery was disassembled in order to observe the state of gas remaining between the electrode plates. As a result, in the batteries of the conventional example, both those having gas retention and those without gas existed, and even in the case of gas retention, the retention amount and the retention state were various and not constant. On the other hand, in the batteries of the first and second embodiments, no stagnation of gas was found. This shows that the gas generated during the pre-charging by the decompression process effectively escaped from between the electrode plates. This decompression process improves the battery performance, and at the same time, ensures stable quality lithium ion A secondary battery can be provided.

The depressurizing condition for performing the depressurizing treatment is 50
When a similar test was carried out at a setting of about 700 mmHg, it was proved to be effective for gas emission, and the effect was particularly remarkable at 400 mmHg or less. However, application of a reduced pressure below the vapor pressure of the electrolytic solution is difficult because it involves boiling of the electrolytic solution.

[0029]

As described above, according to the present invention, the gas remaining between the electrodes constituting the power generating element is removed by the decompression treatment, so that the gas that inhibits charging and discharging does not remain, and the lithium ion secondary The effect of increasing the discharge capacity of the battery and decreasing the internal resistance is obtained. In addition, variations in discharge capacity and internal resistance are reduced, and an effect of providing improved battery performance in a stable state can be obtained.

[Brief description of the drawings]

FIG. 1 shows a configuration example of a lithium ion secondary battery.
Sectional view.

FIG. 2A is a flowchart illustrating a procedure of a manufacturing process according to a first embodiment, and FIG. 2B is a flowchart illustrating a manufacturing process according to a second embodiment.

FIG. 3 is a graph showing a frequency distribution of a discharge capacity by a charge / discharge test.

FIG. 4 is a graph showing a frequency distribution of internal resistance in a charge / discharge test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing lid 3 Electrode group

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Miura 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Terms (reference) 5H011 AA09 BB04 FF02 GG07 5H028 AA08 BB01 BB05 BB07 BB10 CC12 5H029 AJ14 AK03 AL06 AM01 BJ14 CJ01 CJ13 CJ16 DJ02 DJ04 DJ09 5H030 AA09 AA10 AS20 BB18

Claims (3)

[Claims] 1. A battery case containing an electrode group and an electrolyte formed by winding a positive electrode plate and a negative electrode plate into a wound structure with a separator interposed therebetween, and precharging the battery case before closing the opening of the battery case. And performing a pressure reduction process at a predetermined pressure during or after the preliminary charging, and then closing an opening of the battery case. 2. A step of accommodating an electrode plate group in which a positive electrode plate and a negative electrode plate are formed in a wound structure with a separator interposed therebetween from an opening end of the battery case and injecting an electrolyte. Before sealing the open end of the battery case, a pre-charging step, a step of reducing the pressure at a predetermined pressure after this pre-charge step, and then a step of sealing the open end of the battery case are performed. A method for producing a lithium ion secondary battery, comprising: 3. A step of accommodating an electrode plate group formed by winding a positive electrode plate and a negative electrode plate into a battery case from the opening end of the battery case with a separator interposed therebetween and injecting an electrolytic solution. Before closing the open end of the battery case, after performing a step of performing pre-charging while reducing the pressure at a predetermined pressure, the battery case is manufactured by a process procedure of closing the open end of the battery case. A method for manufacturing a lithium ion secondary battery.