JPH07245105A - Non-aqueous electrolyte secondary battery and its positive electrode active material - Google Patents

Abstract

(57) [Abstract] [Purpose] A secondary battery using a non-aqueous electrolyte, and by improving the positive electrode active material, provides a battery having excellent discharge performance after high temperature storage. [Structure] A positive electrode active material in which the whole or a part of the surface of lithium nickelate was covered with lithium carbonate was used. This reduces the contact surface between the lithium nickel oxide and the non-aqueous electrolyte, eliminates the formation of a film that inhibits the discharge reaction that may be caused by decomposition of the electrolyte, and improves the deterioration of discharge performance after storage at high temperature. be able to.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery,
In particular, it relates to improvement of a battery using a lithium composite oxide as a positive electrode active material.

[0002]

2. Description of the Related Art In recent years, portable and cordless AV equipment or electronic equipment such as personal computers have been rapidly developed, and there has been a demand for a secondary battery having a small size, a light weight and a high energy density as a power source for driving them. high. In this respect, non-aqueous secondary batteries, particularly lithium secondary batteries, are highly expected as batteries having high voltage and high energy density.

Lithium nickel oxide (LiNiO ₂ ) capable of intercalating lithium has been proposed as a positive electrode active material satisfying the above demands. However, when left at a high temperature, there are problems that the active material deteriorates significantly and discharge performance deteriorates, and it has not yet been commercialized.

On the other hand, it is known that LiNiO ₂ reacts with carbon dioxide to form lithium carbonate and nickel oxide (Journal of Catalyst 132,
92, 1991) is LiN coated with lithium carbonate.
It is not known whether iO ₂ is effective as a positive electrode active material for batteries.

[0005]

LiNiO ₂ exhibits a potential of 4 V or more with respect to lithium, and when this is used as a positive electrode active material, a secondary battery having a high energy density can be expected. However, its storage characteristics are poor, and the capacity deterioration rate is particularly large during storage at high temperatures.

[0006]

In order to solve the above problems, the present invention uses LiNiO ₂ whose entire surface or a part thereof is coated with lithium carbonate as a positive electrode active material. It has been found that the use of such a positive electrode active material makes it possible to obtain a non-aqueous electrolyte secondary battery having a low storage characteristic, particularly a small capacity deterioration rate at high temperature storage.

[0007]

Function: LiNiO ₂ has a large deterioration rate of discharge capacity after storage at high temperature. The cause is not clear, but LiNiO
Direct contact between ₂ and non-aqueous electrolyte decomposes non-aqueous electrolyte,
A film that inhibits the discharge reaction is formed on the surface of iNiO ₂ . This is considered to be one of the factors that increase the deterioration of discharge capacity during good storage at high temperature.

In the present invention, LiNiO, which is the positive electrode active material, is used.
By coating the entire surface or a part of the surface of ₂ with lithium carbonate, the contact surface between LiNiO ₂ and the non-aqueous electrolytic solution is reduced, and a reaction film with the electrolytic solution which is thought to be formed by decomposition of the electrolytic solution is formed. Therefore, the present invention aims to improve the deterioration of the discharge performance after storage at high temperature.

[0009]

The present invention will be described below with reference to the drawings and specific embodiments.

The method for preparing the positive electrode active material LiNiO ₂ whose surface is coated with lithium carbonate is as follows. Lithium hydroxide and nickel hydroxide are compounded so that the ratio of lithium and nickel is 1: 1 in stoichiometry, and after mixing. Bake at 700 ° C. for 5 hours.
The firing atmosphere at that time was an oxygen atmosphere. Next, the surface of LiNiO ₂ is coated with lithium carbonate. A method of coating the surface with lithium carbonate is as follows.
Leave at 0 ° C for 2-3 minutes or in air at 200 ° C
The surface of LiNiO ₂ is covered with lithium carbonate by leaving it to stand for 10 minutes.

FIG. 1 shows a model diagram thereof. Confirmation of lithium carbonate can be confirmed by X-ray photoelectron spectroscopy analysis or infrared spectroscopy analysis. In addition, the coating state is in close contact with the surface of LiNiO ₂ in a layered form, and the thickness of the layer is 10 to 100.

[0012]

[Outer 1]

It is a degree. Next, in order to evaluate the deterioration of the discharge capacity during high-temperature storage when the obtained positive electrode active material was used in a battery, a cylindrical battery was prototyped and studied. 100 parts by weight of the above positive electrode active material, 4 parts by weight of acetylene black, and 7 parts by weight of a fluororesin binder were mixed to prepare a positive electrode mixture, which was suspended in a carboxymethylcellulose aqueous solution to form a paste. Apply this paste to both sides of aluminum foil,
After drying, it was rolled into an electrode plate.

The negative electrode was made into a paste by mixing 100 parts by weight of a carbon material obtained by firing coke and crushing it with 10 parts by weight of a fluororesin binder and suspending it in an aqueous solution of carboxymethyl cellulose. Then, this paste was applied on both sides of a copper foil, dried and rolled to obtain a negative electrode plate.

FIG. 2 is a vertical sectional view of a cylindrical battery constructed by using these electrode plates. The battery consists of a strip-shaped positive electrode plate,
A lead was attached to each of the negative electrode plates, which were spirally wound with a polypropylene separator interposed therebetween, and the spirally wound plate was housed in a battery case. As the electrolytic solution, a solution obtained by dissolving lithium perchlorate at a ratio of 1 mol / 1 in a mixed solvent of equal volume of propylene carbonate and ethylene carbonate,
A test battery was prepared by injecting a predetermined amount of this and sealing the case.

In FIG. 2, reference numeral 1 is a battery case formed by processing an organic electrolytic solution resistant stainless steel plate, 2 is a sealing plate provided with a safety valve, and 3 is an insulating packing. Reference numeral 4 denotes an electrode plate group. The positive electrode plate and the negative electrode plate are spirally wound via a separator and housed in a case, the positive electrode lead 5 is connected to the sealing plate 2, and the negative electrode lead 6 is pulled out from the negative electrode. Connected to the bottom of the battery case 1. Insulating rings 7 are provided on the upper and lower portions of the electrode plate group 4, respectively.

This test battery was subjected to a constant current charge / discharge test at room temperature for up to 5 cycles under the conditions of a charge / discharge current of 100 mA, a charge end voltage of 4.1 V and a discharge end voltage of 3.0 V, and then left at 60 ° C. for 20 days. A charge / discharge test similar to the above was conducted at room temperature.

FIG. 3 shows the discharge performance after leaving at 60 ° C. for 20 days. As a comparative example, the discharge characteristics of conventional LiNiO ₂ whose surface is not coated with lithium carbonate are also shown.

As can be seen from FIG. 3, LiNiO ₂ whose surface is coated with lithium carbonate shows excellent discharge performance even after being left at 60 ° C. for 20 days, but LiNiO ₂ whose surface is not coated at all has discharge capacity. Is deteriorated.

In this embodiment, a carbon material which lithium adsorbs or intercalates is used as the negative electrode, but the same effect can be obtained by using lithium metal or lithium alloy in addition to this. Similar results were obtained even if some of the nickel was replaced with other transition metals.

Similar results were obtained even when the lithium carbonate coating did not completely cover the entire surface of LiNiO ₂ , but only a part thereof.

[0022]

As is apparent from the above, according to the present invention, by using LiNiO ₂ whose surface is coated with lithium carbonate as the positive electrode active material, the contact surface between LiNiO ₂ and the non-aqueous electrolyte solution is reduced. By doing so, it is possible to eliminate the formation of a film that inhibits the discharge reaction that is thought to be caused by the decomposition of the electrolytic solution, and it is possible to obtain a non-aqueous electrolytic solution secondary battery having excellent discharge performance even after storage at high temperature.

[Brief description of drawings]

FIG. 1 is a model diagram illustrating the present invention.

FIG. 2 is a vertical sectional view of a cylindrical battery according to an embodiment of the present invention.

FIG. 3 is a diagram showing a comparison of discharge performance between the present invention and a comparative example battery.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Insulation Packing 4 Electrode Plate Group 5 Positive Electrode Lead 6 Negative Electrode Lead 7 Insulation Ring

(72) Inventor Kaoru Inoue 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Masatoshi Nagayama, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the whole or part of the surface of lithium nickelate is coated with lithium carbonate. 2. A non-aqueous electrolytic solution secondary battery comprising a non-aqueous electrolytic solution in which lithium nickelate whose surface is entirely or partially covered with lithium carbonate is used as a positive electrode active material and lithium is used as a negative electrode active material.