The silicon compound having such half-value width and crystallite size may improve the battery characteristics because of low crystallinity and a small abundance of Si crystal. Further, when the silicon compound having low crystallinity like this is present, a stable silicon compound may be generated.

Further, as the composition of the silicon compound to be prepared, x is preferably closer to 1. This is because high cycle characteristics may be obtained. Still further, the composition of the silicon compound in the present invention does not necessarily mean purity of 100%, and may contain a slight amount of impurities.

Further, the silicon compound may be composited with a carbon material. As a method of compositing, there are methods of preparing a carbon film on a surface of the silicon compound such as a thermal CVD (Chemical Vapor Deposition) method, a method of physically mixing the silicon compound and the carbon material, or the like. By compositing the carbon material with the silicon compound, high conductivity may be imparted.

In particular, as a method of generating the carbon film on the surface of the silicon compound, the thermal CVD method is desirable. In the thermal CVD method, first, the silicon compound is set in a furnace. Then, a hydrocarbon gas is filled in the furnace followed by elevating an inner furnace temperature. By elevating the inner furnace temperature, the hydrocarbon gas is decomposed and the carbon film is formed on a surface of the silicon compound. A decomposition temperature of the hydrocarbon gas is not particularly limited but is desirably not higher than 1200° C., and particularly desirably not higher than 950° C. This is because unintended disproportionation of the silicon compound may be suppressed.