Polyimide capping layer on improving electrochemical stability of silicon thin-film for Li-ion batteries

Silicon (Si) is a promising anode material for LIBs due to its high theoretical gravimetric capacity of 3570 mAh g⁻¹ , which is about ten times higher than that of graphite. However, the large volume expansion of Si during lithiation gives rise to non-trivial mechanical challenges and constraints which hinder widespread commercial adoption. In particular, electrode cracking and delamination destroy the intrinsic electrical connectivity in the Si electrodes, leading to rapid capacity degradation upon cycling. Herein, we demonstrate a novel approach of capping Si thin-film electrodes with a high strength polyimide by electro-spraying to overcome the pulverization and mechanical issues during cycling. The polyimide layer provides mechanical support to the Si thin-film and maintains its capacity during cycling, with a high capacity of 2610 mAh g⁻¹ at 100 mA g⁻¹ and no capacity loss after 300 cycles at 3500 mA g⁻¹ . Furthermore, in situ dilatometry tests reveal that the polyimide capping layer enables reversible electrode thickness change during lithiation and de-lithiation, thus improving the cycling performance. This work provides a practical manufacturing strategy for commercializing silicon-based electrode films.