Method of producing silicon oxide, negative electrode active material for lithium ion secondary battery and lithium ion secondary battery using the same

1. A method for producing a silicon oxide, wherein:

a vapor deposition apparatus is utilized, the vapor deposition apparatus comprising a vacuum chamber, a gas supply inlet for supplying an oxygen-containing gas into the vacuum chamber, a pressure reduction outlet for reducing pressure inside the vacuum chamber and an electron beam heater, and

the method comprises steps of:

(a1) disposing a metal substrate and a target essentially consisting of silicon inside the vacuum chamber;

(a2) creating an oxygen atmosphere by supplying the oxygen-containing gas from the gas supply inlet, while reducing pressure inside the vacuum chamber;

(a3) heating the target with the electron beam heater for evaporating silicon atoms from the target;

(a4) forming a silicon oxide layer on the substrate by reaction between the evaporated silicon atoms and oxygen in the oxygen atmosphere; and

(b) obtaining silicon oxide particles by separating the silicon oxide layer from the substrate and then pulverizing the separated silicon oxide layer,

wherein a molar ratio of oxygen atoms to silicon atoms in the silicon oxide particles is 0.2 to 0.9.

2. The method of claim 1 , wherein:

the vapor deposition apparatus further comprises, inside the vacuum chamber a unit for converting the oxygen-containing gas into plasma, and

the method further includes, before the step (b), a step (c) of converting the oxygen-containing gas into plasma.

3. The method of claim 1 , wherein an average particle size of the silicon oxide particles is 0.5 to 20 μm.

4. The method of claim 1 , wherein said target consisting of silicon has a purity of 99.9999%.

5. The method of claim 1 , wherein the metal substrate has a high melting point.

6. The method of claim 1 , wherein the metal substrate includes iron or steel.