Electrolyte-philic and thermal-resistant polyimide separator enhances the performance of flexible silicon/carbon nanofibers for lithium-ion batteries

It is still challenging to construct a stable silicon/electrolyte interface to inhibit the mechanical fracture of Si particles and repeated formation of a solid electrolyte interface layer. The separator is a vital component in lithium-ion batteries, however, commercial polyolefin separators suffer from low thermal stability and poor electrolyte wettability. Herein, a polyimide separator is reported to achieve a stable interface of silicon anode due to its high polarity, outstanding electrolyte absorption, and reduction of side reactions. The binder-free self-standing silicon carbon (Si@C) nanofiber composite is designed by a facile electrospinning method and subsequent pyrolysis, where the nanosized Si particles are confined in polyimide-derived carbon nanofibers to form a bamboo-like morphology with good flexibility. Such flexible nanofiber film with cross-linked 3D network structure is important to increase energy density of batteries, mitigate the growth of new interfaces, and avoid the known issues of side reaction during the electrochemical operation. Encouragingly, the 40 %-Si@C composite illustrates an improved lithium storage property with high reversible capacity of 1819.7 mAh g−1 at 0.2 A g−1, excellent rate capability and cycling stability, demonstrating superiority of the film electrode and polyimide separator. This work provides new insights for stabilizing the interface electrochemistry of alloy anodes for the development of next-generation flexible energy storage devices.