Electrochemical properties of non-nano-silicon negative electrodes prepared with a polyimide binder

We successfully improved the cycle stability of a silicon (Si) negative electrode that consisted of untreated, conventional micro-sized Si particles by applying polyimide (PI) with a low breaking elongation percentage and a high tensile strength as a binder. The strong adhesion of the PI binder suppresses the collapse of the Si negative electrode undergoing the expansion/contraction of Si particles during lithiation/delithiation so that the PI-Si electrode maintains a discharge capacity of 800 mAh g super(-1) during 195 cycles at a current density of 800 mA g super(-1). The electrodes prepared in this study contain a PI binder of 15 wt.% to maintain the electrode structure. Such a comparatively large amount of PI binder may prevent Li-ion access into Si particles. Nevertheless, the present Si negative electrode with sufficient electronic conductivity maintains a discharge capacity of 800 mAh g super(-1) during 167 cycles even at a high rate (1600 mA g super(-1)). Perhaps the PI binder does not hinder Li-ion access to Si particles. The cell containing a highly porous polyolefin film coated with ceramic as a separator for a facile supply of Li ion from a bulk electrolyte shows excellent cycle stability and maintains a discharge capacity of 800 mAh g super(-1) during 300 cycles.