Improvement in Si active material particle performance for lithium-ion batteries by surface modification of an inductivity coupled plasma-chemical vapor deposition

The high capacity and optimal cycle characteristics of silicon render it essential in lithium-ion batteries. The authors have attempted to realize a composite material by coating individual silicon (Si) particles of a few micrometers in diameter with a silicon oxide film to serve as an active material in the anode and so optimize the charge-discharge characteristics of the lithium-ion battery. Particle coating was achieved using an inductively coupled plasma-chemical vapor deposition (ICP-CVD) process that realized a homogenous coating of silicon oxide film on each Si particle. The film was synthesized based on tetraethyl orthosilicate (TEOS), with hydrogen (H ₂) 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 H ₂ flow during the silicon oxidization deposition with ICP-CVD. The silicon oxide covering the Si particles included both silicon monoxide and suboxide, which served to optimize the charge-discharge characteristics. The authors have succeeded in realizing a favorable active material using Si which is abundant in nature in the anode of a lithium-ion battery with highly charged, optimized cycle properties.