Alloy Design for Long Term Cyclability of Si Based Anode Materials for Lithium Ion Batteries

Composites comprising silicon (Si), graphite (C) and polyacrylonitrile based disordered carbon (PC), denoted as Si/C/PC, have been synthesized by thermal treatment of high energy mechanically milled silicon, graphite, and polyacrylonitrile (PAN) powder of nominal composition 42wt.%C-28wt.%Si-30wt.%PAN. The resultant Si/C/PC composite exhibits a 1^st charge capacity of ∼1015mAh/g with a fade in capacity ∼0.31% per cycle when cycled at a rate of ∼160mA/g. In order to improve the cyclability of the Si/C/PC composite system, the alloying/dealloying behavior of lithium ion with silicon has been studied to minimize the volume expansion/contraction during electrochemical cycling, and accordingly changes in the alloy composition has been proposed to fulfill the requirements for practical application.