JP2003031222A - Cathode active material for non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide conditions enabling practical determination of a positive active material for a lithium secondary battery, which is stable for a long time in a slurry. SOLUTION: This positive active material is represented by the general formula, Lix Ni1-y Ay O2 . (0.98<=x<=1.06, 0.05<=y<=0.30; A is at least one of Co and Al.) The material of 5 g is mixed by stirring in 100 g of pure water for 120 minutes, then the mixture solution is left standing for 30 seconds, pH of the obtained supernatant liquid is 12.7 or less at 25 deg.C. Preferably, the pH is 12.0 or more but 12.7 or less at 25 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, portable electronic devices for consumer use,
With the rapid progress of cordless technology, batteries with high energy density are attracting attention.

However, if the operating voltage of the positive electrode is low or the discharge capacity is small, it is difficult to obtain a battery having a high energy density. Therefore, for example, lithium acid having a layered structure as disclosed in Japanese Patent Laid-Open No. 05-290845. Nickel, Japanese Patent Laid-Open No. 05-290890 and Japanese Patent Laid-Open No. 05-290890
As disclosed in Japanese Patent Publication No.-283076, there has been proposed a nickel-lithium-based positive electrode active material in which a part of nickel is replaced with another metal element such as Co or Mn.

When a battery is produced using such a positive electrode active material, a powder of the positive electrode active material is mixed with polyvinylidene fluoride (PVDF) which is a binder and carbon which is a conductive additive, and N- It is common to prepare a positive electrode by slurrying it with an organic solvent such as methyl-2-pyrrolidone (NMP) and applying it to a current collector such as Al foil.

[0005]

A nickel lithium-based positive electrode active material is a PVDF and carbon, N
In the case of slurrying with MP, the viscosity was often increased and gelation occurred, which often made stable coating on the current collector difficult. Here, the gelling of the slurry refers to a state in which the fluidity and uniformity are lost due to the increase in viscosity, and when the gelling is extremely advanced, the coating on the current collector becomes impossible. Become.

In addition, in the case of mild gelation, the resistance value of the manufactured electrode sheet is greatly affected, and the battery characteristics such as the discharge capacity and rate characteristics of the battery manufactured using the manufactured electrode sheet are deteriorated. The task was to do so.

In Japanese Patent Laid-Open No. 10-79244, in order to solve this problem, even when a highly basic electrode active material and a binder which is easily modified under basic conditions are combined, It has been proposed that the problem of gelation can be solved by adding an inorganic acid or an organic acid when mixing.

In order to elucidate the cause, the present inventor has found that the gelation of the slurry, the specific surface area of the positive electrode material, the particle size distribution, the water content and the Li / M ratio (where M is other than Li in the positive electrode active material). The correlation with metal elements) and the amount of residual lithium was examined in detail, but no clear relationship was observed.

Therefore, from the above-mentioned various characteristics of the positive electrode material, it is not possible to accurately determine whether or not gelation occurs during the preparation of the slurry, and when the material is synthesized from the raw material, the Li component and other metals are not used. Even if the charged composition of the elemental components is strictly controlled, some materials may gel during the preparation of the slurry after a manufacturing process such as mixing and firing.
It was also found that some gels did not gel.

As described above, it is very difficult to determine in advance the positive electrode material that does not gel.

An object of the present invention is to provide a condition that allows practical determination of a positive electrode active material for a lithium secondary battery that is stable in a slurry for a long time.

[0012]

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is Li _x Ni _1-y A _y O ₂ (0.98 ≦
x ≦ 1.06, 0.05 ≦ y ≦ 0.30, A is Co, A
5% of pure water
It is desirable that the pH of the supernatant obtained by stirring and mixing in 0 g for 120 minutes and then standing for 30 seconds is 12.0 or more and 12.7 or less at 25 ° C.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solve the above-mentioned problems, the present inventor synthesized various Li _x Ni _1-y A _y O ₂ to obtain a specific surface area, particle size distribution, water content of a positive electrode active material, The Li / M ratio (where M is a metal element other than Li in the positive electrode active material), the amount of residual lithium, and the pH of the supernatant after the positive electrode active material is put into pure water and stirred, The relationship with gelation was examined in detail. As a result, they have found that there is a high correlation between the pH of the supernatant after the positive electrode material is poured into pure water and stirred, and the gelation during slurry preparation, and the present invention has been completed.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is Li _x Ni _1-y A _y O ₂ (0.98 ≦ x ≦ 1.06,
0.05 ≦ y ≦ 0.30, A is a composition of at least one of Co and Al), but this composition range is necessary for ensuring battery characteristics.

5 g of Li _x Ni _1-y A _y O _{2 was} added to pure water 10
When the pH of the supernatant obtained by stirring and mixing in 0 g for 120 minutes and then standing for 30 seconds exceeds 12.7 at 25 ° C., the cause is unknown as described above, but gelation occurs during slurry preparation. I found out. Therefore, the pH is 12.
It must be 7 or less, but when the positive electrode active material is washed with water or pickled and Li in the positive electrode active material is extracted to lower the pH, the crystallinity of the positive electrode material may change. The pH is preferably 12.0 or more and 12.7 or less, since the battery characteristics may be deteriorated.

The pH in the present invention is measured as follows.

5 g of the synthesized positive electrode active material powder was mixed with 10 parts of pure water.
Pour into a 200 ml beaker containing 0 g, 12
After stirring for 0 minutes, the mixture was allowed to stand for 30 seconds, and the pH of the obtained supernatant was measured using a composite electrode (manufactured by Horiba Ltd., model number 6366-10).
PH measuring instrument equipped with D) (manufactured by Horiba, model number F-2
It measured using 3).

In the pH measurement, the mass of the positive electrode active material,
The mass of pure water is defined by the principle that, if the mass ratio is the same, the mass of pure water has the same pH for the same positive electrode active material. This is because if the area is smaller than the opening area, the pH will gradually drift toward the acidic side during measurement due to the influence of carbon dioxide gas in the air, and accurate measurement cannot be performed. Usually used 100-20
About 100 ml of pure water is suitable for a 0 ml beaker, and the amount of pure water in the present invention was 100 g. It is within the scope of the present invention to increase or decrease the amount of pure water to about 50 to 150 g or to make the amount suitable for the container.

The temperature is specified because the pH changes with temperature.

Further, the stirring time after charging the positive electrode active material is 1
The reason for defining 20 minutes is that the pH gradually increases from immediately after the positive electrode active material is poured into pure water to about 60 minutes, and then stabilizes after that. Further, if the mixture is stirred for too long, the pH becomes inaccurate due to the influence of carbon dioxide gas in the air, so about 120 minutes is appropriate.

Further, the upper limit of the pH of the supernatant after the positive electrode active material is poured into pure water and stirred is defined by the pH of 12.7.
This is because when it exceeds, gelation occurs during slurry adjustment.

The mechanism by which the slurry gels is as follows:
A series of reactions in which PVDF reacts with a trace amount of water in the slurry to cause dehydrogenation of PVDF or a crosslinking reaction,
It is considered that the slurry becomes highly viscous due to the presence of an alkaline component such as Li, leading to gelation.

By the way, this gelation is judged by the specific surface area of the positive electrode active material, the particle size distribution, the water content, the Li / M ratio (where M is a metal element other than Li in the positive electrode active material), the amount of residual lithium, etc. The reason why it cannot be done is not clear so far, but it is speculated as follows. That is, it is considered that the gelation is not caused, for example, by the residual lithium being dissolved in the slurry, but is caused solely by the Li itself in the layered compound, which is the positive electrode active material, being dissolved in the slurry. It is presumed that there is no effective determination method other than pH measurement because the ease with which Li is removed from the layered crystal depends on the subtle differences in the conditions during the synthesis of the positive electrode active material.

The gelation of the slurry was determined according to the following evaluation method.

PVDF was added to 20 g of the positive electrode material powder.
(Kureha Chemical Industry, model number KF Holmer # 1100) 2.
2 g and 9.6 ml of NMP (manufactured by Kanto Chemical Co., Ltd.) are weighed and put in a container, and 2000 rp with a kneader (manufactured by Nippon Seiki Seisakusho, product name Non-Bubbling Kneader, model number NBK-1)
Mix well for 10 minutes at a rotation speed of m.

The paste-like slurry thus obtained was transferred to a glass bottle, sealed, and then stored in a dry box at a temperature of 25 ° C. and a dew point of −40 ° C., and the state of the slurry after a certain period of time was observed.

The embodiments of the present invention will be described in detail below.

Examples 1 to 5 Li _x Ni _1-y A _y O ₂ (0.98 ≦ x ≦ 1.06, which is a layered compound and has various compositions),
0.05 ≦ y ≦ 0.30, A is at least one of Co and Al), and LiOH.H ₂ O and N are used as starting materials.
It was prepared as follows using i _1-y A _y (OH) ₂ (manufactured by Sumitomo Metal Mining Co., Ltd.).

An appropriate amount of each raw material was weighed, thoroughly mixed, heat-treated in oxygen at 350 ° C. for 3 hours, and then further mixed.
Li _x N, which is a layered compound, is baked at 50 ° C for 24 hours.
A positive electrode active material of i _1-y A _y O ₂ was obtained. As a result of chemical analysis, the obtained positive electrode active material was Li-Ni-C as shown in Table 1.
Each molar composition was o-Al. From these, x,
y is calculated.

The pH values measured as described above for the positive electrode active materials obtained in Examples 1 to 5 are also shown in Table 1.

Gelation tests were performed on the positive electrode active materials obtained in Examples 1 to 5.

In the gelation test, as described above, the state of the slurry 24 hours after the preparation of the slurry was visually and visually observed. In the present invention, as a criterion for the quality judgment in the gelation test, the one having a fluidity in the slurry even after being left for 24 hours was marked with ◯, and the gelled gelled product was marked with x.

Table 1 also shows the results of the quality judgment of the gelation test.

[0034]

[Table 1]

(Comparative Examples 1 to 4) In the same manner as in Examples,
Table 2 shows the results of chemical synthesis of Li _x Ni _1-y A _y O ₂ having various compositions as a layered compound. The pH measured as described above is also shown in Table 2.

Gelation tests of the positive electrode active material powders obtained in Comparative Examples 1 to 4 were carried out in the same manner as described above, and the results of quality judgment were also
The results are shown in Table 2.

[0037]

[Table 2]

[0038]

As is apparent from the examples, the positive electrode active material whose pH measured as described above falls within the range of the present invention is:
It can be seen that all of them have fluidity even after 24 hours have passed since the slurry was prepared and have excellent gelation resistance.

Therefore, the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is stable for a long time in a slurry containing an organic solvent, a conductive auxiliary agent, and a fluorine-based binder.

Claims (2)

[Claims] 1. Li _x Ni _1-y A _y O ₂ (0.98 ≦ x ≦
1.06, 0.05 ≦ y ≦ 0.30, A is at least one of Co and Al), and 5 g is 100 g of pure water
A positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that the pH of the supernatant obtained by stirring and mixing therein for 120 minutes and then standing for 30 seconds is 12.7 or less at 25 ° C. 2. Li _x Ni _1-y A _y O ₂ (0.98 ≦ x ≦
1.06, 0.05 ≦ y ≦ 0.30, A is at least one of Co and Al), and 5 g is 100 g of pure water
After stirring and mixing in the solution for 120 minutes, the pH of the supernatant obtained by allowing to stand for 30 seconds has a pH of 12.0 or higher at 25 ° C.
A positive electrode active material for a non-aqueous electrolyte secondary battery, which is 2.7 or less.