Electrochemical reactivity of polyimide and feasibility as a conductive binder for silicon negative electrodes

A novel polyimide has been investigated as a conductive binder for silicon electrodes. The electrochemical properties of a polyimide electrode, derived from pyromellitic dianhydride and 4,4′-oxydianiline, were characterized and the feasibility as a binder for silicon electrodes was investigated. When fully lithiated and delithiated (3 V–5 mV), the polyimide electrode demonstrates a large reversible capacity of 826 mAh g−1 in the first cycle. The ex situ IR spectra indicate that the carbonyl groups on imide rings are irreversibly reduced during earlier period of first lithiation. Further lithiation leads to removal of characteristic peaks of PO–PI as well as a significant decrease of peak intensities, which implies changes in chemical structure of the host material. Nevertheless, the PO–PI electrode delivers large reversible capacity in subsequent cycles. In the potential range that silicon operates (0.7 V–5 mV), the polyimide electrode remains in a highly lithiated state maintaining its electric conductivity. Silicon electrodes with polyimide binder exhibit superior capacity retention and coulombic efficiency in comparison to electrodes using insulating binders. The improvements are attributed to the reinforced electrical conductive network in the electrode laminate.