JPS5832749B2 - Manufacturing method for positive electrode active material for organic electrolyte batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a fluorocarbon positive electrode active material for a battery using a light metal such as lithium as a negative electrode active material and an organic electrolyte.

Organic electrolyte batteries that use lithium for the negative electrode and carbon fluoride for the positive electrode are known as high-energy density batteries, and are being widely put into practical use.

However, when this battery system was strictly examined, it was found that the properties of the fluorinated carbon in the positive electrode active material had a considerable effect on the discharge characteristics and storage characteristics.

In other words, impurities remaining in the fluorinated carbon produced during the process of fluorinating carbon powder, especially unstable fluorides such as higher-order fluorides, or adsorbed fluorine, can cause variations in the open circuit voltage or initial discharge voltage of the battery. It has been found that this has an unstable effect, and that it also has an adverse effect on storage properties, such as an increase in self-discharge accompanied by corrosion reactions.

The present invention relates to a method for producing a fluorocarbon active material that eliminates the above-mentioned conventional drawbacks and provides an organic electrolyte battery with excellent performance.

Conventionally, fluorocarbon has been produced by reacting carbon powder with low-strain pure fluorine scum or fluorine gas diluted with an inert gas, such as argon or nitrogen.

This fluorocarbon naturally contains unstable higher order fluorides or adsorbed fluorine due to the high reactivity of fluorine gas.

A possible method for removing this problem is to wash the fluorocarbon with an acidic or alkaline solution, but this method has the disadvantage of increasing the number of manufacturing steps.

In the production of fluorocarbon, the present invention involves the presence of oxygen in the fluorine gas that reacts with the carbon powder, thereby containing high-order fluorides, etc., which may have an adverse effect on batteries, in the fluorocarbon produced. This is based on the discovery that the amount of acid is significantly lower.

In other words, a battery using fluorinated carbon obtained through the reaction of oxygen-containing fluorine gas and carbon powder as a positive electrode active material had a constant open circuit voltage, and there was no instability in the voltage at the initial stage of discharge. .

Furthermore, regarding the storage characteristics, which are very important for secondary batteries, the decrease in discharge capacity and increase in battery internal resistance over the storage period have been greatly improved compared to conventional batteries.

In fact, when conventional fluorocarbon is immersed in an organic electrolyte,
Fluorine ions, which promote corrosion of battery internal materials and cause polymerization of organic electrolytes, are detected in considerable amounts, but are hardly detected in the fluorinated carbon according to the present invention.

This fluorine ion is caused by higher-order fluoride or adsorbed fluorine, but in order to prevent these from being generated, the inventors' experiments have shown that at least a volume of oxygen gas is added to the fluorine gas. It is desirable that the ratio is 3 or more.

The reason for this is that the fluorine content (1ooxF/(C+F)) of fluorocarbon produced by the conventional method is 62 to 65 by weight, and the theoretical fluorine content of fluorocarbon (CF)n is 61 , 4. This means that the fluorine content is several factors larger than that of the four weight factors.

It is thought that this corresponds to higher-order fluoride or adsorbed fluorine, and therefore, it seems that an oxygen gas of 3 or higher was necessary to suppress this.

Regarding the upper limit, as the oxygen content increases and the partial pressure of fluorine gas decreases, the reaction rate (time) slows down, so an appropriate value is adopted from the viewpoint of productivity, but the desired effect of the present invention cannot be determined. There were no particular restrictions.

In practical use, air can be used instead of pure oxygen for economical reasons.

When air is used, it is practically effective to add 15% to 90% by volume of the fluorine gas.

In this case, the ratio of oxygen gas to fluorine gas corresponds to about 3 parts to 180 parts.

The present invention will be explained below with reference to Examples.

Petroleum coke carbon powder with a particle size that can pass through a 200 mesh sieve is thoroughly dried.

This carbon powder was reacted with fluorine gas diluted with air (air:fluorine=5=1 (volume ratio)) at a temperature of 400° C. for 2 hours to obtain fluorinated carbon.

Let this be A.

In this case, the ratio of oxygen to fluorine is 100 by volume.
%.

For comparison, fluorocarbon B obtained by reacting fluorine gas diluted with nitrogen gas according to the conventional method, and fluorocarbon B obtained by washing with a caustic potassium aqueous solution of 30% by weight C
was used.

A battery was assembled using these three types of fluorocarbons as follows.

Fluoride carbon, acetylene black as a conductive material, and tetrafluoroethylene resin powder as a binder in a weight ratio of 75:1.
The mixture was mixed at a ratio of 5:10, and this was pressure-molded into a predetermined reticulated titanium current collector to form a positive electrode.

The negative electrode was made by crimping lithium metal onto a nickel net current collector.

An electrolytic solution containing 1 mol/l of lithium borofluoride (LiBF4J) dissolved in r-butyrolactone was used.

The battery was inserted into a battery case with a polypropylene nonwoven fabric interposed between the positive and negative electrodes and sealed.

The drawing shows battery a made using the above fluorocarbons A, B, and C.
It showed the characteristics of /, S/, and C/.

The solid line is a discharge curve immediately after the prototype was produced, which was discharged at 0.5 A (10 hour rate).

The dotted line is a discharge curve obtained by discharging under the same conditions after being stored at 70° C. for 3 months, which is a fairly harsh condition.

As can be seen from this figure, battery A' using the active material according to the present invention shows a flat voltage immediately after the start of discharge,
In addition, there is only slight deterioration after storage.

On the other hand, the conventional battery B' shows a gradual voltage drop after the start of discharge, which is thought to be caused by high-order fluoride, and the voltage flatness is also poor.

Moreover, the deterioration after high temperature storage is quite large.

In addition, battery C using fluorocarbon C that has been treated with alkali
′ has greatly improved characteristics compared to B′, but
It doesn't reach A.

This is probably because high-level fluorides are not removed sufficiently, but it is difficult to completely remove them with this operation, and the operation is also very complicated.

The table below shows the amount of fluorine detected in the electrolyte when fluorocarbons A, B, and C were immersed in the electrolyte.
showed that.

As expected, A is very small.

As described above, according to the present invention, the performance of an organic electrolyte battery can be improved.

[Brief explanation of drawings]

The drawing shows a comparison of the discharge characteristics of batteries using various fluorocarbons.

Claims (1)

[Claims] 1. A method for producing a positive electrode active material for an organic electrolyte battery, characterized in that fluorocarbon is obtained by reacting fluorine gas and carbon powder in the presence of oxygen gas. 2. The method for producing a positive electrode active material for an organic electrolyte battery according to claim 1, wherein the amount of the oxygen gas is at least 3% by volume of the fluorine gas.