JPH07226231A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To increase overcharge capability in high temperature atmosphere of a lithium secondary battery using vanadium pentoxide in a positive electrode. CONSTITUTION:A case 1 also serving as a positive terminal and a sealing plate 2 also serving as a negative terminal are insulatingly sealed through a polypropylene gasket 3, and a positive electrode 4 made of vanadium pentoxide is arranged so as to come in contact with the case 1. A negative electrode 5 made of a compound of lithium with niobium pentoxide or a lithium alloy is faced to the positive electrode 4 through a separator and brought into contact with the sealing plate 2. An organic electrolyte is used as the electrolyte, and 3-20wt.% aluminium powder is added to the positive electrode 4 to increase overcharge capability in high temperature atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a rechargeable lithium secondary battery used as a mobile DC power source, a backup power source and the like.

[0002]

2. Description of the Related Art Due to recent rapid development of technology in the electronics field, miniaturization of electronic devices has progressed, and there has been an increasing demand for batteries having a small size, light weight, and high energy density as a power source for those devices. As such a battery, a lithium secondary battery using lithium as a negative electrode has been attracting attention and is being actively developed. Among them, a lithium secondary battery using vanadium pentoxide for the positive electrode and a lithium alloy or lithium niobium pentoxide and its compound for the negative electrode is known.

When a lithium alloy is used for the negative electrode, it is expected to be used as a battery system capable of greatly improving high energy density at high voltage, and especially when a compound of lithium and niobium pentoxide is used for the negative electrode. It is expected to be a battery system that can significantly improve the discharge cycle life.

[0004]

However, it has been found that in such a battery system, the battery capacity significantly decreases when overcharged in a high temperature atmosphere. This mechanism is not clear, but it is considered as follows. Since vanadium pentoxide is charged at a high position of 3.4 to about 4 VvsLi, a high potential is applied to the positive electrode during overcharge, and part of the positive electrode vanadium pentoxide is oxidized to form vanadate ions. Dissolves in electrolyte. The dissolved vanadate ions are reduced on the negative electrode lithium alloy or lithium-doped niobium pentoxide electrode, and at the same time,
The solvent in the electrolytic solution is oxidized. It is considered that the oxidation product of the solvent forms a film on the negative electrode and suppresses the charge / discharge reaction.

An object of the present invention is to provide a highly reliable lithium secondary battery with improved overcharge characteristics in this type of battery system.

[0006]

The positive electrode mixture of these batteries generally contains about 90% vanadium pentoxide, and is composed of carbon black and a binder in several% each. Further, aluminum powder is added. The amount of aluminum powder added is effective over a wide range, but 3 to 20 wt% is most effective for the positive electrode mixture.

[0007]

[Function] By adding aluminum powder to the positive electrode mixture, the overcharge characteristic is improved.

Although the reason for the effect is not clear, it is considered that the addition of aluminum powder to the positive electrode causes the oxidation of aluminum to precede the formation of vanadate ions by the oxidation of vanadium pentoxide.

It is considered that this aluminum oxide is stably present in the positive electrode mixture and does not adversely affect the electrochemical reaction of vanadium pentoxide.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the coin-type lithium secondary battery of the present invention. As shown in the figure, a case 1 also serving as a positive electrode terminal and a sealing plate 2 also serving as a negative electrode terminal are insulated by a polypropylene gasket 3.

The positive electrode 4 and the negative electrode 5 are separated by a separator 6 made of polypropylene microporous film. In this example, in order to examine the effect of the amount of aluminum powder added to the positive electrode 4, vanadium pentoxide was set to a fixed amount of 100 mg, and aluminum powder was added to the positive electrode mixture in an amount of 0, 1, 2, respectively.
3,5,10,20,30,40 wt%, 5 wt% of carbon black as a conductive material and 5 wt% of fluororesin as a binder were mixed and kneaded. This was molded into a pellet having a diameter of 13 mm and a thickness of about 0.5 mm, and dehydrated by high temperature vacuum drying to prepare a positive electrode mixture. For the negative electrode 5, first, 90 wt% of niobium pentoxide, 5 wt% of carbon black as a conductive material, and 5 wt% of fluororesin as a binder were kneaded so as to have a weight ratio of 13 mm in diameter and 0.5 mm in thickness. It was prepared by molding into pellets of a size, vacuum drying at high temperature, and dehydration treatment. Lithium foil having a diameter of 10 mm and a thickness of 0.1 mm was adhered to the mixture pellet, and lithium perchlorate was immersed in a propylene carbonate solution in which 1 mol / l was dissolved, and lithium was doped into niobium pentoxide. Is. The electrolytic solution contains propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1:
A solvent prepared by dissolving 1 mol / l of lithium perchlorate in the solvent mixed in 1 was used. The size of the battery is 16 mm in diameter and 1.6 mm in thickness.

Although these batteries are fully charged at 1.8 V or more, they are stored in an overcharged state where a constant voltage of 2.0 V is applied to these batteries in an atmosphere of 60 ° C.
A constant resistance discharge of 2 kΩ was performed in an atmosphere of ° C, the discharge capacity from 2 V to 1 V was measured, and the ratio to the measured value immediately after assembly, that is, the residual rate of the discharge capacity was obtained. The result is shown in FIG.

As is clear from FIG. 2, the residual rate increases when even a small amount of aluminum powder enters. In particular, when the amount of aluminum powder added is about 3 wt%, the effect is large, and when it is 20 wt%, it becomes almost saturated. With a real battery,
Since the size is limited, the minimum volume and weight are preferable. Therefore, the optimum addition amount of aluminum powder is 3 to 20.
wt%.

Although lithium-doped niobium pentoxide was used as the negative electrode in this embodiment, the same effect as in this embodiment can be obtained even when a lithium alloy such as an alloy of lithium and aluminum is used as the negative electrode. It was

[0015]

As is apparent from the above examples, according to the present invention, by adding aluminum powder to the positive electrode mixture, the overcharge characteristics in a high temperature atmosphere can be improved and the reliability of the overcharge characteristics can be improved. It is what provides a high lithium battery at times.

[Brief description of drawings]

FIG. 1 is a sectional view of a coin-type lithium secondary battery in an example of the present invention.

FIG. 2 is a diagram showing the relationship between the amount of aluminum powder added and the residual rate of discharge capacity.

[Explanation of symbols]

 1 case 2 sealing plate 3 gasket 4 positive electrode 5 negative electrode 6 separator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Chikayama 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A positive electrode containing vanadium pentoxide as a main component,
What is claimed is: 1. A rechargeable lithium secondary battery comprising a negative electrode containing lithium as a main component and an organic solvent in which a lithium salt is dissolved as an electrolytic solution, wherein aluminum powder is added to the positive electrode. 2. The lithium secondary battery according to claim 1, wherein the addition amount of the aluminum powder is 3 to 20 wt% with respect to the positive electrode mixture.