Silicon-thermally modified polyimide with optimized charge transfer complex structure for enhanced Li-ion storage

Abstract

Thermally modified polyimide (PI) is investigated as an efficient binder to enhance the Li-ion storage performance of silicon nanoparticles. Heat-treatment of Si@PI electrodes results in an optimized charge transfer complex (CTC) structure, which improves the electrochemical performance of the electrode by forming a compact structure that reduces the charge transfer impedance, significantly enhancing the cycling performance of the silicon anode. Electrodes subjected to the heat-treatment at 350 °C (Si@PI-350) exhibit a charge transfer impedance of 37.67 Ω combined with a reversible Li+ storage capacity of 2334 mAh g−1 recorded after 30 cycles at 200 mA g−1, in comparison to the original Si@PI electrodes showing an enhanced impedance value of 130.4 Ω and reduced capacity of 737 mAh g−1. At a high current density of 2000 mA g−1, the capacity of Si@PI-350 (1001 mAh g−1) is significantly greater than Si@PI (455 mAh g−1) highlighting the efficiency of the CTC structures formed during the thermal treatment. We suggest that the thermal treatment of Si@PI electrodes at optimal conditions can significantly affect the Li-ion insertion/extraction cycling performance of silicon nanoparticles.