Preparation method of silicon-based composite negative electrode material for lithium battery

A preparation method of a silicon-based composite negative electrode material for a lithium battery, comprising the following steps:

• (1) drying a raw material A capable of generating SiOx (0<x≤2) steam and a raw material B, wherein the raw material B is capable of reacting with a SiOx vapor to generate a silicate in a non-oxidizing atmosphere;
• (2) vaporizing the dried raw material A and the dried raw material B under vacuum, mixing the vapor of the raw material A and the vapor of the raw material B, and condensing and depositing to obtain a deposited material;
• and
• (3) crushing the deposited material to obtain particles having a median particle size of 1-20 μm, and apply a carbon coating to the particles to obtain the silicon-based composite negative electrode material;
• wherein the raw material A in the step (1) is one or a combination of two or more of silicon powder, silicon monoxide powder, and silicon dioxide powder;
• the raw material B is selected from at least one of alkali metal, alkaline earth metal, a third main group elementary substance, oxides thereof, and alloys thereof, with the proviso that the alloys account for 30 wt % or more of the raw material B and comprises magnesium;
• wherein the vaporization in the step (2) is realized through a vacuum furnace with a deposition system that comprises two or more heating cavities,
• wherein the raw material A is placed in a first heating cavity having a heating temperature of 1200-1600° C. and the raw material B is placed in a second heating cavity having a heating temperature of 1000-1200° C.,
• wherein a size of a gas path through which vapor from the two or more heating cavities enters the deposition system is adjustable, and a flow rate of the vapor entering the deposition system is a volume flow ratio of the vapor of the raw material A to the vapor of the raw material B is 100:(1-20).