Synthesis of anode active material particles for lithium-ion batteries by surface modification via chemical vapor deposition and their electrochemical characteristics

The high capacity and optimal cycle characteristics of silicon render it essential in lithium-ion batteries. We have attempted to realize a composite material by coating individual silicon (Si) particles of μm-order diameter with a silicon oxide film to serve as an active material in the anode of a lithium-ion battery and thus improve its charge-discharge characteristics. The particles were coated using an inductively coupled plasma-chemical vapor deposition (ICP-CVD) process that realized a homogeneously coated silicon oxide film on each Si particle. The film was synthesized using tetraethyl orthosilicate (TEOS) with hydrogen (H₂) gas used as a reducing agent to deoxidize the silicon dioxide. This enabled the control of the silicon oxidation number in the layers produced by adjusting the H₂ flow during the silicon oxide deposition by ICP-CVD. The silicon oxide covering the Si particles included both silicon monoxide and suboxide, which served to improve the charge-discharge characteristics. We succeeded in realizing an active material using Si, which is abundant in nature, for the anode of a lithium-ion battery with highly charged, improved cycle properties.