JPH07335259A - Manufacture of lithium secondary battery - Google Patents

Abstract

PURPOSE:To form a protective film, not relating with battery electrode reaction, on a positive/negative electrode surface by charging a battery at voltage of specific % rated voltage of the secondary battery within a specific number of days after assembling the battery, and thereafter applying or holding charging voltage for a prescribed time or more under the specific % atmosphere. CONSTITUTION:Powder is prepared by mixing respectively 5wt.% graphite and acetylene back as a conducting agent and 5wt.% PVDF as a binder relating to, for instance, 85 pts.wt. LiCoO2 as a positive electrode active material, to add dimethylforumamide and isophorone to the powder as a solvent. A positive electrode substance thus obtained is applied to an Al late and dried to obtain a positive electrode plate. Next by mixing, for instance, 70wt.% pitch cokes capable of doping/dedoping an Li ion, 10wt.% conduction agent acetylene black and 20wt.% fluorine system binder, solvent dimethylforumamide or the like added to be applied to an Ni plate, to obtain a negative electrode plate. After charging at 98 to 100% rated voltage of a secondary battery within three days after assembly, the plate is preserved for two hours or more under the atmosphere of 30 to 70 deg.C.

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 lithium secondary battery.

[0002]

2. Description of the Related Art A lithium secondary battery comprises a positive electrode, lithium and / or a lithium occlusion negative electrode, a separator and a non-aqueous electrolyte interposed between the positive and negative electrodes, and a case for accommodating them. When a positive electrode and a negative electrode are arranged in this case via a separator and a non-aqueous electrolytic solution is poured into the case to assemble a battery, the manufacturing is completed in a discharged state.

Further, LiCoO 2 is used as an active material for the positive electrode.
Lithium-metal composite oxide such as ₂ is used, and the negative electrode is
A lithium carrier made of a carbonaceous material that can be doped with Li ions and dedoped is used.
Ions move to the positive electrode side, and Li ions move to the negative electrode side during charging.

Since this lithium secondary battery can obtain a high battery voltage and a high energy density, it is used in various fields such as a power supply for memory backup of a computer.

[0005]

However, in such a lithium secondary battery, in addition to the electrode reaction as the original battery at the time of charging / discharging, L on the surface of the positive and negative electrodes.
While consuming i ions, a decomposition reaction of the electrolytic solution occurs, and a secondary reaction such as formation of a kind of film on the positive and negative electrode surfaces proceeds. For this reason, as the charge / discharge cycle is repeated, the Li ions involved in the electrode reaction decrease and the electrolytic solution deteriorates, and the film on the positive and negative electrode surfaces suppresses the original electrode reaction. Therefore, there is a problem of deterioration of the cycle characteristics such that the discharge capacity decreases, which becomes remarkable especially when a large current is passed.

Further, even if the battery is simply stored without being charged / discharged, the electrolytic solution is exposed to a large potential difference between the positive and negative electrodes, so that the above-mentioned secondary reaction proceeds and the discharge capacity decreases. There was also a problem of deterioration of storage characteristics.

The present invention has been made in view of the above problems, and an object thereof is to provide a method for manufacturing a lithium secondary battery capable of improving cycle characteristics and storage characteristics.

[0008]

In order to achieve the above object, the present invention provides a method for producing a lithium secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte, respectively. The secondary battery is charged at a voltage of 98% to 100% of the rated voltage of the secondary battery within 3 days after its assembly, and then stored in an atmosphere of 30 ° C to 70 ° C for at least 2 hours or more.

Further, in order to achieve the above-mentioned object, the present invention provides a method for producing a lithium secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte, respectively. The battery is charged at a voltage of 98% to 100% of the rated voltage of the secondary battery within 3 days after assembly, and then the charging voltage is applied for at least 2 hours and stored in an atmosphere of 20 ° C to 70 ° C.

[0010]

In the lithium secondary battery manufactured by the method of the present invention, cycle characteristics and storage characteristics are improved. In particular, these characteristics are further improved when the storage is performed with the charging voltage applied.

The reason for this is presumed as follows.

According to the present invention, after charging the battery at a voltage of 98% to 100% of the rated voltage of the secondary battery within 3 days after assembling the battery, the charging voltage is kept for at least 2 hours in an atmosphere of 30 ° C to 70 ° C. When applied or stored without applied, a kind of protective film that does not participate in the battery electrode reaction is formed on the positive and negative electrode surfaces. Therefore, this protective film suppresses secondary reactions such as decomposition reaction of the electrolytic solution on the electrode surface, and thus cycle characteristics and storage characteristics are improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

The method for manufacturing the lithium secondary battery of this embodiment comprises a conventional assembling process and a post-treatment process which will be described later, and Examples 1 and 2 will be described below.

Example 1 First, a process for assembling a spiral type lithium secondary battery having a rated voltage of 4.2 V will be described.

In producing the positive electrode plate, 5 parts by weight of graphite and acetylene black as the conductive agent were added to 85 parts by weight of LiCoO ₂ as the positive electrode active material, respectively.
Polyvinylidene fluoride (PVDF) as binder
Was mixed with dimethylformamide as a solvent and isophorone in a ratio of 1: 1 to the powder prepared by mixing 5% by weight of k. The positive electrode active material slurry thus obtained was applied to an aluminum plate (20 μm in thickness in this example), dried, and rolled to prepare a positive electrode plate.

Next, in producing the negative electrode plate, first, Li
70% by weight of pitch coke as a carbonaceous material capable of ion doping and dedoping, 10% by weight of acetylene black as a conductive agent, and 2% of a fluorine-based binder.
A powder prepared by mixing 0% by weight was mixed with dimethylformamide as a solvent and isophorone in a ratio of 1: 1 and kneaded. The slurry of the negative electrode mixture thus obtained was applied to a nickel plate (20 μm in thickness in this example) and then dried to prepare a negative electrode plate.

A separator made of a polyethylene porous film is interposed between the positive electrode plate and the negative electrode plate obtained as described above and spirally wound to form a power generating element. The power generating element is housed in a negative electrode can, and then propylene. Li in a mixed solvent of carbonate, ethylene carbonate and diethyl carbonate
The assembly process of the spiral type lithium secondary battery was completed by impregnating the non-aqueous electrolyte obtained by dissolving 1 mol / l of PF ₆ .

Next, the post-treatment process of the battery which has completed the above assembling process will be described.

First, the battery which had been assembled for 3 hours was 4.1.
The first charge (first charge) was performed at 5V. After that, the production was completed by storing it in an atmosphere of 45 ° C. for 24 hours. This storage was performed without applying a voltage to the battery.

A comparison test of the cycle characteristics of the battery adopting the manufacturing method of this embodiment and the conventional battery was conducted. In this cycle test, the post-treatment process is performed by changing the storage conditions for the batteries 3 hours after the assembly, and the capacities at the 10th cycle and the 100th cycle are measured for the batteries having different storage conditions. The capacity ratio at the cycle was calculated as the capacity ratio (%). Further, similarly to the conventional method, the capacity ratio of the battery in the discharged state, which was manufactured only by the assembly process, was measured without storage.

The storage conditions of the post-treatment process were changed such that the charging voltage was 4.1 to 4.25 V, the storage temperature was 10 ° C. to 80 ° C., and the storage time in the non-application state was 2 hours to 48 hours.

Regarding the voltage of charging performed when measuring the capacity,
The battery subjected to the post-treatment step had the same voltage as the charging voltage in the post-treatment step, and the conventional non-preserved cell had a rated voltage of 4.2V. The charge / discharge end voltage was 2.5V.

Table 1 shows the capacities at the 10th cycle with respect to the charging voltage during storage. 10 the higher the charging voltage
The capacity at the second cycle is large.

[0025]

[Table 1] The comparison test results of the above cycle characteristics are shown in FIGS.
Shown in. In the figure, compared to the conventional one without storage,
The capacity ratio is excellent when the charging voltage shown in FIGS. 1B and 1C is 4.15 V and 4.2 V, and when the storage temperature is in the range of 30 ° C. to 70 ° C. These charging voltages of 4.15V and 4.2V correspond to 98.8% and 100% of the rated voltage 4.2V, respectively. Further, the capacity ratio is further excellent in the storage temperature range of 40 ° C to 60 ° C.

Further, as shown in FIG. 2, a cycle test was conducted on a battery which was subjected to a post-treatment step while changing the storage period from immediately after assembling to the first charging within a range of 3 hours to 5 days. This cycle test includes 10th cycle and 10th cycle.
The capacity at the 0th cycle was measured, and the capacity ratio at the 100th cycle to the 10th cycle was calculated as a capacity ratio (%). The storage condition during the post-treatment process is the charging voltage 4.2.
V, the storage temperature was 50 ° C., and the storage time in the non-application state was 24 hours. In FIG. 2, the capacity ratio (discharge capacity ratio) is excellent when the battery is assembled within 3 days.

Example 2 The assembly process of the spiral type lithium secondary battery of this example is the same as that of Example 1, and only the post-treatment process is different. Therefore, the description of the assembly process is omitted and only the post-treatment process is performed. explain.

In the post-treatment process of this example, the battery 3 hours after assembly was charged at 4.15V. Then 4
The production was completed by storing in an atmosphere of 5 ° C. for 24 hours. This storage was performed with a voltage of 4.15 V applied to the battery.

A comparative test of the cycle characteristics of the battery adopting the manufacturing method of the present embodiment and the conventional battery was conducted under the same conditions as in the case of the first embodiment.

As shown in FIGS. 3 (a) and 3 (b), the capacity ratio is superior to the conventional one without storage when the charging voltage is 4.15V and 4.2V. This is the case where the storage temperature is in the range of 20 ° C to 70 ° C. These 4.15
V and 4.2V charging voltage is rated voltage 4.2V respectively
Corresponding to 98.8% and 100%.

Further, a comparison test of the storage characteristics of the battery adopting the manufacturing method of this embodiment and the conventional battery was conducted. In this comparative test, each battery immediately after production was charged for the first time, and then stored for 1 month in each atmosphere of 20 ° C., 45 ° C. and 60 ° C. Was measured. The capacity recoverability was defined as the ratio of the capacity when the battery was recharged after being stored for one month and then recharged to the capacity when the battery was initially charged.

With respect to the battery of the manufacturing method of this embodiment, the battery 3 hours after the assembly was charged for the first time at 4.2 V, and then a voltage of 4.2 V was applied in an atmosphere of 50 ° C. Batteries stored for 24 hours were used, and conventional batteries were not stored, and batteries charged for the first time immediately after assembly were used.

The test results, as shown in Table 2, show that the remaining capacity and recoverability of the present example are clearly superior to those of the conventional case.

The capacity at the time of first charging is
In the case of the present embodiment, it is 406 mAh, whereas in the conventional case it is almost the same as 405 mAh.

[0035]

[Table 2] As described above, Examples 1 and 2 are excellent in cycle characteristics and storage characteristics as compared with the case where the post-treatment process is not performed after the conventional assembly. Also, FIGS. 1B and 1C and FIG.
Comparing (a) and (b), the cycle characteristics of Example 2 are slightly better than those of Example 1. This is considered to be because in the case of Example 2, a voltage was applied during storage after the first charge to compensate for the capacity decrease due to self-discharge. Further, during storage after the first charging, the voltage is applied in the second embodiment, whereas the voltage is not applied in the first embodiment, and thus the first embodiment is superior in cost.

[0036]

As described above, in the lithium secondary battery manufactured by the manufacturing method of the present invention, the cycle characteristics and the storage characteristics are improved. In particular, these characteristics are further improved when the storage is performed with the charging voltage applied.

[Brief description of drawings]

FIG. 1 is a graph comparing the cycle characteristics of a battery according to the present invention which is not applied during storage and a conventional battery.
(D) has charging voltages of 4.1V, 4.15V,
This is the case of 4.2V and 4.25V.

FIG. 2 is a graph showing cycle characteristics with respect to time until the first charging after assembling the battery according to the present invention.

FIG. 3 is a graph comparing the cycle characteristics of a battery applied during storage according to the present invention and a conventional battery, and (a) and (b) are charging voltages of 4.15V and 4.2V, respectively. is there.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kohei Yamamoto 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd.

Claims (2)

[Claims] 1. A method of manufacturing a lithium secondary battery, each comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte, wherein the secondary battery is manufactured within 3 days after assembly. A method for producing a lithium secondary battery, which comprises charging the battery at a voltage of 98% to 100% of a rated voltage and then storing the battery in an atmosphere of 30 ° C to 70 ° C for at least 2 hours or more. 2. A method for producing a lithium secondary battery, each comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte, the method comprising the steps of: A method for manufacturing a lithium secondary battery, which comprises charging the battery at a voltage of 98% to 100% of a rated voltage and then applying and storing the charging voltage in an atmosphere of 20 ° C. to 70 ° C. for at least 2 hours or more.