Among all the materials used as cathode active material in lithium ion secondary batteries, silicon oxide powder is preferred because it increases the initial capacity of the cell. However, it is very expensive. Therefore, a method to increase the yield and reduce the cost of silicon oxide powder is necessary. The present invention provides a method of producing silicon oxide powder which is inexpensive and efficient.

The method is based on the reaction between a metallic silicon species of high purity and a silicon dioxide powder. It involves a combination of heat and reduced pressure to form silicon oxide powder. The powder is largely amorphous, which reduces the volume change during charge.

The raw material powder mixture is preferably heated in a non-oxidating atmosphere to a temperature of 800 to 1,100deg C. The powder is then pulverized to a desired particle size. It is then contacted with the surface of the substrate to fuse together.

After fusion, the resulting mixture is transferred into a reaction vessel. An oxygen gas is then fed to the SiO gas, forming a gas mixture. The gas mixture is then cooled with a coolant. The reactivity of the reaction is enhanced when the temperature and the pressure of the gas mixture are kept low.

The amount of metal silicon powder is ideally matched with the silicon dioxide powder in order to produce a balanced molar ratio. The average particle size of the starting material is usually between 0.1 and 20 mm.

tags: semiconductor semiconductor material