JP2000208148A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deterioration of a positive electrode and improve the cycle characteristic by adding anhydrous LiOH particle to the positive electrode. SOLUTION: A binder is dissolved in an organic solvent, and an active material and a conductive agent are mixed thereto followed by stirring. Finely pulverized anhydrous LiOH particle is mixed thereto followed by stirring to form a paste. The paste is printed on an aluminum current collecting foil, and drying, cutting and pressing are performed to complete a positive electrode. Since the anhydrous LiOH particle adsorbs the moisture from the air or the moisture originally contained in the material, the influence of moisture can be reduced by adding the anhydrous LiOH particle. The addition quantity of the anhydrous LiOH to the positive electrode is preferably set within the range of 0.3-1.1 wt.% to the positive electrode active material. According to this, the cycle characteristic of a lithium secondary battery can be improved, and the paste to be printed on the aluminum current collecting foil is prevented from being gelled by the inclusion of water in the manufacture of the positive electrode to make the formation of the positive electrode difficult.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium ion secondary battery, and more particularly to an improvement of a positive electrode for a lithium ion secondary battery.

[0002]

2. Description of the Related Art It has been known that a self-discharge characteristic is improved by coating the periphery of a positive electrode active material used in a lithium ion secondary battery with LiOH.
This is considered to be due to the reason that the decomposition of the organic electrolytic solution is suppressed by the LiOH coating. For example,
JP-A-4-169076 also discloses that an alkali metal hydroxide is added to the positive electrode, which suppresses the decomposition of the organic electrolytic solution or reacts with the decomposition product to cause a solvent decomposition product. Techniques for reducing the deterioration of battery performance have been disclosed.

[0003]

However, in the above prior art, when adding an alkali metal hydroxide to the positive electrode, for example, a method of adding and mixing LiOH as an aqueous solution is adopted. With this method, 8
Although a drying step of about 10 hours at 0 ° C. is performed, the drying is insufficient, and there has been a problem that moisture is left in the positive electrode and deterioration of the positive electrode occurs due to generation of an acid such as HF. In addition, when moisture is present in an alkali metal hydroxide such as LiOH, the paste containing the positive electrode active material tends to gel at the time of forming the positive electrode, and there has been a problem that electrode formation becomes difficult.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object the purpose of trapping moisture around the positive electrode, suppressing the deterioration of the electrode due to the generation of acid, and improving the cycle characteristics. It is to provide a lithium ion secondary battery having:

[0005]

In order to achieve the above object, the present invention is a lithium ion secondary battery, characterized in that anhydrous LiOH particles are added to a positive electrode.

In the above-mentioned lithium ion secondary battery, the anhydrous LiOH particles may be used in an amount of 0.3 to 0.3% with respect to the positive electrode active material.
It is characterized by being added at 1.1 wt%.

[0007]

Embodiments of the present invention (hereinafter, referred to as embodiments) will be described below.

As a result of investigations by the present inventors to improve the cycle characteristics of the lithium ion secondary battery, they have found that the cycle characteristics can be improved by adding a small amount of anhydrous LiOH particles to the positive electrode. This is anhydrous LiOH
Since the particles have an effect of adsorbing and trapping water, the water present in the positive electrode can be suppressed from reacting with the electrolytic solution,
It is considered that the generation of acid can be reduced.

In order to produce the positive electrode used in the lithium ion secondary battery according to the present invention, PVd is first dissolved in an organic solvent.
The binder such as F is dissolved, and the active material and the conductive material are mixed and stirred. Next, anhydrous LiOH particles pulverized to a size of 100 μm or less are mixed with the mixture and stirred to form a paste. Here, the reason why the anhydrous LiOH is pulverized to 100 μm or less is to prevent the particle size of the anhydrous LiOH particles from becoming too large with respect to the thickness of the electrode. Further, the paste manufactured as described above is printed on an aluminum current collector foil, dried, cut, and pressed to complete a positive electrode. In this case, drying is performed at 175 ° C. for 1 hour.

As described above, when the anhydrous LiOH particles are added to the positive electrode, the water adsorbed from the air during the production of the positive electrode and the water originally contained in the material are adsorbed.
The effect of moisture can be reduced as compared with the case where the positive electrode is simply dried by heating.

FIG. 1 shows that the conductive material is 0.4 to 1.0 wt% and the binder is 0.2 to 1.0 wt% based on the positive electrode active material.
5 shows the measurement results of the rate of deterioration of the capacity of the lithium ion secondary battery in the case where the organic solvent is mixed with 5 to 15 wt% and the amount of anhydrous LiOH is variously changed. The capacity deterioration rate is obtained as a rate of decrease in capacity per charge / discharge when charge / discharge is repeated 80 times at 60 ° C. As can be seen from FIG. 1, even if the amount of anhydrous LiOH added to the positive electrode is small or large, the deterioration rate is deteriorated. Therefore, it can be seen that there is an optimum range for the amount of anhydrous LiOH added.

For example, the lithium ion 2 according to the present invention
When the secondary battery is used in an EV vehicle, the required durability of the battery is to guarantee 100,000 km running at normal temperature (25 ° C.). This is lithium ion 2
When evaluated as the number of times of charging and discharging of the secondary battery, it is possible to travel about 300 km with one charging, and it is necessary to perform about 300 charging and discharging to guarantee 100,000 km. However,
As the usage time becomes longer, the lithium ion secondary battery deteriorates and the distance that can be traveled by one charge decreases. Therefore, in order to actually guarantee 100,000 km, 500 km is required.
It is necessary to guarantee the charge and discharge of about once while maintaining a practical level of battery capacity. As such a practical level of battery capacity, the capacity after 500 charge / discharge cycles is 50% of the initial capacity.
It is necessary to secure above.

The above description is for a case where a lithium ion secondary battery is used at room temperature. However, when charging and discharging are performed at a high temperature of about 60 ° C., the deterioration rate is about 6 times higher than that at room temperature (25 ° C.). Double. Therefore, in a high-temperature charge / discharge test at 60 ° C., if the battery capacity is 50% or more after about 80 charge / discharge cycles, the capacity after 500 charge / discharge cycles at normal temperature should be 50% or more. Becomes possible. The deterioration rate of the battery in this case is 0.6 (% / c
y) It must be:

Referring to FIG. 1, the deterioration rate is 0.6 (% / c).
y) It can be seen that the amount of anhydrous LiOH added to the positive electrode should be in the range of 0.3 to 1.1 wt% based on the positive electrode active material in order to be less than y). If the addition amount of anhydrous LiOH is further reduced, a sufficient effect cannot be obtained, and if the addition amount is increased, the periphery of the positive electrode active material is completely covered by LiOH having high electric resistance, and the resistance of the electrode increases. In either case, the improvement of the cycle characteristics of the lithium ion secondary battery cannot be sufficiently achieved.

In the above-described conventional method, the capacity deterioration rate after charging and discharging 500 times at normal temperature is 1.5 (% / cy).
This indicates that the present invention can greatly improve the cycle characteristics of the lithium ion secondary battery.

Further, instead of the normal temperature as described above,
In order to guarantee a running of 30,000 km at a high temperature of about ℃, it is necessary to make the conditions stricter than the above. In this case, since the number of times of charge / discharge determined from the distance traveled by one charge described above is 100 times, it is necessary to set this to 0.5 (% / cy) or less in terms of the capacity deterioration rate. Become.
In this case, as can be seen from FIG.
The addition amount of iOH is 0.5 to 0.9 with respect to the positive electrode active material.
It can be seen that it is wt%.

As described above, by adding anhydrous LiOH particles to the positive electrode, water mixed in the positive electrode can be adsorbed and the adverse effect of the water can be removed, thereby improving the cycle characteristics of the lithium ion secondary battery. be able to.
In addition, it is possible to solve the problem that the paste for printing on the aluminum current collector foil is gelled due to the incorporation of moisture when the positive electrode is formed, making it difficult to form the positive electrode. further,
The step of removing moisture from the positive electrode by heating and drying or the like becomes unnecessary, and the process can be simplified.

[0018]

As described above, according to the present invention,
Since water is adsorbed and trapped by the anhydrous LiOH particles added to the positive electrode, generation of acid due to water mixed in the positive electrode can be suppressed, and the cycle characteristics of the lithium ion secondary battery can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of LiOH added to a positive electrode and the capacity deterioration rate of a lithium ion secondary battery using this positive electrode.

Claims (2)

[Claims] 1. A lithium ion secondary battery characterized in that anhydrous LiOH particles are added to a positive electrode. 2. The lithium ion secondary battery according to claim 1, wherein the anhydrous LiOH particles are added in an amount of 0.3 to 1.1 wt% based on a positive electrode active material. .