JP3223523B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having an improved positive electrode.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery using lithium, a lithium alloy or a lithium compound as a negative electrode is expected to have a high voltage and a high energy density, and much research has been conducted.

In particular, Mn is used as a positive electrode active material for these batteries.
O_TwoAnd TiS_TwoHas been well studied. These positive electrode active materials
As for the quality, the potential with respect to Li is about 3 V.
Mn _TwoO_FourAnd LiCoO_TwoIs more than 4V with respect to Li
It is attracting attention as a positive electrode active material showing a potential.

That is, efforts have been made to increase the battery voltage as well as the capacity as a means for obtaining a high energy density of the battery.

[0005] Among them, LiCoO ₂ is considered to be promising as a positive electrode active material because it has a large discharge capacity and may have excellent charge / discharge cycle characteristics.

Further, in order to improve the charge / discharge cycle characteristics, which is one of the important necessary characteristics as a secondary battery, LiC
Attempts have been made to add Mn, Ni, Cr, Fe, and the like to oO _2, and further improvement of charge / discharge cycle characteristics has been achieved.

[0007]

The use of the above-mentioned positive electrode active material makes it possible to realize a nonaqueous electrolyte secondary battery having a large discharge capacity and excellent charge / discharge cycle characteristics. However, since the charge voltage exceeds 4 V, There is a problem that the high-temperature storage characteristics of the battery after charging are insufficient. High-temperature storage of a non-aqueous electrolyte secondary battery is caused by decomposition of a trace amount of water and electrolyte solvent inside the battery, which causes problems such as an increase in battery internal resistance and a decrease in charge / discharge capacity. In particular, as the battery voltage increases, these phenomena become more remarkable, and become more remarkable during high-temperature storage.

[0008] Regarding moisture brought into the battery,
Efforts have been made to suppress the incorporation of water into the battery by purifying the electrolyte solution, including the distillation process, and drying the positive electrode active material. However, in the case of a secondary battery that needs to be repeatedly charged and discharged, particularly when the charging voltage exceeds 4 V, good high-temperature storage characteristics cannot be obtained only by pretreatment such as removal of water.

[0009] It is considered that the reaction between the positive electrode active material and the electrolyte solution solvent and the reaction between the substance generated by this reaction and the negative electrode active material are likely to occur, and that the performance of the battery is reduced.

An object of the present invention is to solve such a problem and to provide a non-aqueous electrolyte secondary battery having improved high-temperature storage characteristics.

[0011]

In order to solve this problem, a nonaqueous electrolyte secondary battery according to the present invention comprises a positive electrode using a composite oxide represented by LiCoO2 as an active material, a negative electrode capable of inserting and extracting lithium, and It has a non-aqueous electrolyte, and the positive electrode is selected from activated carbon, silica gel, and activated alumina.
At least one is 0.0% to 1 g of LiCoO2.
Use from 02 g to 0.05 g .

[0012]

[0013]

According to this structure, the activity in the positive electrode in the present invention is improved.
At least selected from charcoal, silica gel and activated alumina
One is the residual water and residual water inside the non-aqueous electrolyte secondary battery.
It has the effect of adsorbing Lucari.

In the positive electrode, at least one selected from activated carbon, silica gel, and activated alumina is converted into 1 g of LiCoO 2.
On the other hand, by adding 0.002 g to 0.05 g , it is possible to reduce the water and the alkali such as LiOH which may remain in the positive electrode active material LiCoO 2 inside the battery. It is believed that battery performance and deterioration due to possible high-temperature storage can be reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte secondary battery according to an embodiment of the present invention will be described below with reference to the drawings.

Example 1 A battery is manufactured as follows.

100 g of LiCoO ₂ as a positive electrode active material is mixed with 3.0 g of acetylene black as a conductive agent, 3 g of activated carbon is added and mixed, and 4.0 g of polytetrafluoroethylene resin as a binder is added. The mixture was mixed to form a positive electrode mixture. 0.1 g of the positive electrode mixture was press-formed at a diameter of 17.5 mm at 1 ton / cm ² to obtain a positive electrode. In FIG.
The molded positive electrode 1 is placed in the case 2. A porous polypropylene film as a separator 3 was placed on the positive electrode 1. A lithium plate having a diameter of 17.5 mm and a thickness of 0.3 mm as the negative electrode 4 was pressure-bonded to a sealing plate 5 provided with a polypropylene gasket 6.

As the non-aqueous electrolyte, a solution prepared by dissolving 1 mol / 1 of lithium perchlorate in a propylene carbonate solution was used. The non-aqueous electrolyte thus obtained was added onto the separator 3 and the negative electrode 4. Thereafter, the upper edge of the case 2 was swaged to seal the battery.

Further, the amount of the activated carbon to be added to the positive electrode 1 was also examined, and the range of the added amount is shown in Table 1.

For comparison, a battery was manufactured in the same manner as described above for the positive electrode to which no activated carbon was added.

A high-temperature storage test of the battery is performed by the following method. That is, the battery obtained by the above method was charged at 20 ° C. to 4.2 V at a constant current of 1 mA, and then charged to 4.2 V.
Discharged to V. After 10 cycles of this charge and discharge, the battery was stored at 60 ° C. for 4 weeks after the charge of the 11th cycle was completed. After storage, the temperature was returned to 20 ° C., and the battery was discharged under the same conditions. Here, the capacity retention rate was defined as follows.

Capacity retention rate = 100 × discharged electricity amount at 11th cycle / 1
Discharged electricity at the 0th cycle In addition, the battery was charged after the storage was completed, and then the discharge capacity was evaluated. Here, the capacity recovery rate was defined as follows.

Capacity recovery rate = 100 × discharged electricity amount at the 12th cycle / 1
Electricity Discharge at Cycle 0 FIG. 2 shows the change in the internal resistance of the battery during storage at 60 ° C. for 4 weeks for each battery. In FIG. Was measured.

In the battery to which no activated carbon was added, a sharp increase in the battery internal resistance was observed immediately after storage, and it became 30 Ω or more after 4 weeks. On the other hand, in the battery of the example, the increase in the battery internal resistance is small.

Table 1 shows the positive electrode mixture 1 of each battery.
The initial discharge capacity per g and the capacity retention rate and capacity recovery rate after 4 weeks are shown.

[0026]

[Table 1]

[0027] The battery without addition of activated carbon shows a very large capacity decrease with storage at 60 ° C for 4 weeks. on the other hand,
A battery to which activated carbon is added has a high capacity retention rate and capacity recovery rate. However, the initial capacity of the battery sharply decreases when the weight ratio of activated carbon to LiCoO ₂ exceeds 0.05.

Accordingly, it has been found that it is particularly desirable that the ratio by weight of the activated carbon having a capacity retention ratio of 80% or more and a capacity recovery ratio of 85% or more be in the range of 0.002 to 0.05.

As described above, the addition of the activated carbon to the positive electrode has an effect of suppressing a decrease in capacity due to high-temperature storage.

Example 2 Next, silica gel was studied.

The battery production and high-temperature storage test were conducted in Example 1.
The same was done. In FIG. 3, which shows the change in the battery internal resistance during storage at 60 ° C. for 4 weeks, the batteries without silica gel showed a sharp increase in the battery internal resistance immediately after storage, and after 4 weeks, the battery internal resistance increased to 30Ω or more. Become. On the other hand, in the battery of the example, the increase in the battery internal resistance is small.

Table 2 shows the initial discharge capacity per 1 g of the positive electrode mixture of each battery and the capacity retention rate and capacity recovery rate after 4 weeks.

[0033]

[Table 2]

For a battery without silica gel added, the temperature was 60 ° C.
It shows a very large capacity decrease with storage for 4 weeks. On the other hand, a battery to which silica gel is added has a high capacity retention rate and a capacity recovery rate. However, the initial capacity of the battery is LiCoO
_{When the} weight ratio of silica gel to ₂ exceeds 0.05, the ratio rapidly decreases.

Therefore, it was found that the addition ratio of silica gel having a capacity retention of 80% or more and a capacity recovery of 85% or more was particularly desirable in the range of 0.002 to 0.05.

As described above, the addition of silica gel to the positive electrode has an effect of suppressing a decrease in capacity due to high-temperature storage.

Similar effects were observed when activated alumina was used. Among the studies, the effect on the high-temperature storage characteristics was most remarkable in the case of silica gel.

As described above, in a nonaqueous electrolyte battery using a composite oxide represented by LiCoO 2 as a positive electrode active material, the positive electrode is selected from activated carbon, silica gel, and activated alumina.
At least one to 1 g of LiCoO2
High temperature by adding 0.002g to 0.05g
A non-aqueous electrolyte secondary battery with excellent storage characteristics can be obtained.
You.

Further, the same effect was observed when these adsorbents were mixed and added.

In the above embodiment, 1 mol / mol of the electrolytic solution was used.
The results are for the case of using a propylene carbonate solution in which lithium perchlorate 1 was dissolved. In addition to this as the electrolytic solution, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium borofluoride, and solute were used as solutes. Electrolyte solutions using carbonates such as propylene carbonate and ethylene carbonate and esters such as gamma-butyrolactone and methyl acetate were good. However, when ethers such as dimethoxyethane and tetrahydrofuran were used, the high-temperature storage characteristics were poor, and improvement of the high-temperature storage characteristics by adding a Lewis acid to the electrolyte was not recognized. In the embodiment, it is considered that since the voltage of the positive electrode becomes 4 V or more, ethers are oxidized.

[0041]

As is clear from the above description of the embodiment,
According to the non-aqueous electrolyte secondary battery of the present invention, there is provided a negative electrode capable of inserting and extracting lithium, a positive electrode having a composite oxide represented by LiCoO 2 as an active material, and a non-aqueous electrolytic solution.
Less selected from activated carbon, silica gel and activated alumina
0.002g for 1g LiCoO2
1 g of LiCoO2
By adding 0.002 g to 0.05 g
To obtain a non-aqueous electrolyte secondary battery with good high-temperature storage characteristics.
This has great industrial significance.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

FIG. 2 is a graph showing a change in internal resistance of the battery of Example 1 during storage at 60 ° C.

FIG. 3 is a graph showing a change in internal resistance of the battery of Example 2 during storage at 60 ° C.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Case 3 Separator 4 Negative electrode 5 Sealing plate 6 Gasket

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaki Hasegawa 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-63-121259 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/48-4 / 62 H01M 10/40

Claims (1)

(57) [Claims] A positive electrode comprising a composite oxide represented by LiCoO2 as an active material, a negative electrode capable of inserting and extracting lithium and a non-aqueous electrolyte, wherein the positive electrode contains activated carbon,
At least one selected from silica gel and activated alumina
From 0.002 g to 0.0 g for 1 g of LiCoO2.
Non-aqueous electrolyte secondary battery with 5g added