JPS62139260A - Manufacture of positive active material for organic electrolyte battery - Google Patents

Abstract

PURPOSE:To obtain a positive active material for organic electrolyte battery having good performance in high rate discharge and high temperature storage by forming a thin conductive film of lithium tungstate on the surface of positive active material. CONSTITUTION:A positive active material is immersed and stirred in a aqueous solution of lithium tungstate (Li2WO4), and dried to vaporize moisture, then heated. By this process, a thin layer of Li2WO4 having conductivity is formed on the surface of the active material. Since the surface of the active material is covered with the thin electron conductive layer, addition of conductive material is eliminated, and no gas evolves even when discharge voltage decreased to about 1V. In addition, dissolution of the active material and decrease in capacity are also retarded. Since Li2WO4 or WO3 is lithium ion conductive, diffusion of lithium ion into the active material is no problem.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to surface treatment of a positive electrode active material of an organic electrolyte battery.

BACKGROUND OF THE INVENTION This type of battery has been widely used as a power source for consumer electronic devices because of its high energy density and high reliability. Recently, there have been many attempts to utilize these features to create secondary batteries, but the problem here is the conductive material. When normal carbon is used and the positive electrode capacity becomes rate-limiting,
When the discharge voltage reaches around 1 V, the solvent in the electrolytic solution is decomposed by carbon, which may cause gas generation. Also,
- Even in secondary batteries, the capacity can be increased if a conductive material is no longer required.

Problems to be Solved by the Invention The above phenomenon of gas generation occurs when lithium ions are inserted at around 1V into the layered lattice of carbon added to maintain the electronic conductivity of the positive electrode. The inserted carbon itself acts as a catalyst,
It is said that this occurs due to the decomposition of the electrolyte, and in reality it is sometimes observed in batteries as well.

Since not all of the positive electrode active materials of lithium batteries are highly conductive, the above-mentioned carbon is added in order to avoid polarization due to internal resistance during discharge. Depending on the conditions during discharge, this carbon causes gas generation for the reasons mentioned above. To avoid this phenomenon, primary batteries usually have a negative electrode capacity rate-limiting configuration. However, in secondary batteries, there is a problem with the reversibility of the negative electrode lithium, so this problem is usually avoided by controlling the positive electrode capacity and prohibiting overdischarge. Metal powder can be considered as a conductive material to replace carbon, but since the potential of the positive electrode active material is higher than that of other materials than gold powder or titanium powder, the metal powder will be eluted from the positive electrode, making it difficult to use. However, it is also difficult to use due to cost considerations.

Another idea is to use conductive metal oxides, such as rhenium oxide, as the conductive material.

In this case, it is true that gas generation does not occur, but there are problems with the amount added from the viewpoint of conductivity, the problem that the capacity of the positive electrode decreases as the amount added increases, and the problem of cost, so it is not practical. It's impossible.

As described above, in secondary batteries, the material and properties of conductive additives are a problem, and there are restrictions on the conditions under which they can be used. It provides:

Means for Solving the Problem In order to solve this problem, the present invention immerses a positive electrode active material in an aqueous solution of lithium tungstate (Li2WO4), stirs it, dries it to evaporate water, and then heat-treats it. By doing so, a conductive thin film layer of Li2WO4 is formed on the surface of the positive electrode active material.

According to this configuration, the surface of the active material is covered with an electronically conductive thin film layer, so there is no need to add a conductive material, and even if the voltage reaches around 1V during discharge, no gas is generated and there is no possibility of , problems such as dissolution and capacity reduction are also eliminated. Furthermore, since this Li 2 WO or WO 5 has lithium ion conductivity, there is no problem in the diffusion of lithium ions into the active material.

Example Embodiments of the present invention will be described below with reference to the drawings.

The figure shows a flat type organic electrolyte battery based on lithium and manganese oxide as an example. In the figure, 1 is a case made of corrosion-resistant stainless steel with a thickness of 0.25 mm, 2 is a sealing plate made of the same material, 3 is a lithium sheet with a capacity of 95 mAh, and 4 is an expanded titanium sheet spot-welded to the inner surface of the case. Metal 5 is a manganese dioxide positive electrode, which has an outer diameter of 14.smm and a thickness of 0.6mm. 6 is a polypropylene nonwoven fabric separator;
A predetermined amount of an equal volume mixed solvent of propylene carbonate, ethylene carbonate, and dimethoxyethane having a lithium hexafluorophosphate concentration of mol/6 is injected. 7 is a gasket made of polypropylene.

The positive electrode 5 was prepared by adding 2.6 g of Li2WO4 (0,
After dissolving 01 mol), 86.9 g (1 mol) of commercially available electrolytic manganese dioxide was added and stirred for 2 hours.
Dry at 80'C for 1 hour. Then, dry at 250'C under oxygen gas flow (1e/min).

Heat-treated for 6 hours. When this material is subjected to X-ray diffraction, L
The presence of i2WO4 was confirmed. 10 parts by weight of a fluororesin binder is added to 100 parts by weight and mixed. This o,
32g (a2mAh) is molded to the above dimensions. This molded Mercedes-Benz was dried at 250° C. for 3 hours under a reduced pressure of 5 mm HH, and used for battery assembly. This is called a battery person.

For comparison, electrolytic manganese dioxide was also heat treated under the same conditions, 5 parts by weight of carbon black and 10 parts by weight of carbon black were added to 100 ntJ parts, and then 10 parts by weight of a fluororesin binder was added to each of them. Add and mix. Their 0.27g (e9mAh) and 0.21
g (54mAh)i It was also molded to the above dimensions, dried under the same conditions, and used for battery assembly. Let these batteries be B and C, respectively. The dimensions of each battery are 20 mm in outer diameter and 1.6 mm in total height.

The above battery A-Ci was discharged to OV at 20°C under loads of 1Ω and 3°KΩ, and the discharge capacity and 3
The following table shows the changes in the total height of the battery under a load of 0 to Ω, and the internal resistance value when stored at 60° C. for 40 days.

(Left below) In addition, the battery was charged at 5V-4, but no problems were observed in the capacity, voltage behavior, or battery shape.

As is clear from the above explanation, by forming a film of lithium ions and electronically conductive lithium tungstate (Li2WO4) on the surface of the positive electrode active material,
High rate discharge is possible, sufficient capacity can be obtained, large capacity can be obtained even in low rate discharge, and there is almost no swelling of the battery due to gas generation even when discharged to OV. In addition, no abnormality is observed even when this battery is stored at high temperatures, and its performance is maintained.

Effects of the Invention As described above, the present invention provides Li2WO4 on the surface of the positive electrode active material.
By creating a conductive thin film of.

The present invention provides a method for producing a positive electrode active material for organic electrolyte batteries that has good performance as well as low rate discharge and high temperature storage properties.

[Brief explanation of drawings]

The figure shows a longitudinal cross-sectional view of a flattened pond in an embodiment of the invention. 1... Case, 2... Sealing plate, 3...
...Negative electrode, 4...Positive electrode.

Claims (1)

[Claims] A method for producing a positive electrode active material for a battery comprising a negative electrode using a light metal as an active material, a positive electrode, and an organic electrolyte, the positive electrode being prepared by pre-immersing the positive electrode active material in an aqueous solution of lithium tungstate and drying it. 1. A method for producing a positive electrode active material for an organic electrolyte battery, the method comprising heat-treating the positive electrode active material to form a thin film layer of lithium tungstate on the surface of the positive electrode active material.