Silicon-based composite anodes for Li-ion rechargeable batteries

Si-C and Si-C-Al composite powders have been synthesized by thermal treatment of high-energy mechanically-milled composite precursors comprising graphite, silicon, aluminium and several types of polymers such as poly(acrylonitrile), poly[(o-cresylglycidyl ether)-co-formaldehyde] resin and poly( methacrylonitrile). The polymers have been used to suppress the interfacial diffusion reactions between graphite, silicon and aluminium, which otherwise lead to the formation of electrochemically-inactive SiC and Al4C3 intermetallics during high- energy mechanical milling. The resultant Si-C composite obtained after thermal treatment of mechanically milled powders of nominal composition [52.5 wt% C]-[17.5 wt% Si]-[8 wt% PAN]-[22 wt% resin] exhibits a reversible capacity of similar to 630 mA h g(-1) with excellent capacity retention when cycled at a rate of similar to 160 mA g(-1). On the other hand, the Si-C-Al composite of nominal composition [ 52.5 wt% C] [ 14 wt% Si]-[3.5 wt% Al]-[30 wt% PMAN] exhibits a reversible capacity of similar to 650 mA h g(-1) up to 30 cycles at a charge/discharge rate of similar to 340 mA g(-1). Scanning electron microscopy analysis of electrochemically-cycled electrodes indicates that the microstructural stability and the structural integrity of the Si-C and Si-C-Al composite is retained during electrochemical cycling, contributing to the good cyclability demonstrated by the composites.