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 ∼630 mA h g−1 with excellent capacity retention when cycled at a rate of ∼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 ∼650 mA h g−1 up to 30 cycles at a charge/discharge rate of ∼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.