Patent ID: 8080335

Claim:
A powder material which allows lithium ions to be stored therein and released therefrom electrochemically, comprising: a composite comprising particles of silicon or an alloy containing silicon; and one of a metal oxide and a semi-metal oxide, wherein a Gibbs free energy when one of a metal and a semi-metal constituting the one of the metal oxide and the semi-metal oxide is oxidized is smaller than a Gibbs free energy when the one of silicon and the alloy containing silicon contained in the particles is oxidized, wherein a weight ratio of the one of the metal oxide and the semi-metal oxide to the particles in the composite is within a range of 1/99 to 3/7, wherein the powder material is formed of secondary particles, each comprising an aggregation of primary particles of silicon metal or an alloy thereof bound by metal oxide particles or semi-metal oxide particles coated on the entire surface of the primary particles, and the metal oxide particles or the semi-metal particles are disposed at an interface between the primary particles, wherein the primary particles are microcrystalline having an amorphous phase or are amorphous, and wherein an average particle diameter of the particles of silicon metal or an alloy thereof is within the range of 0.5 μm to 5 μm, an average particle diameter of the metal oxide or semi-metal oxide particle is within the range of 5 nm to 500 nm, and a crystalline size of the silicon metal or the alloy thereof is 100 nm or less.