A polyacrylonitrile (PAN)-based double-layer multifunctional gel polymer electrolyte for lithium-sulfur batteries

Owing to high theoretical capacity, lithium-sulfur batteries (LSBs) are receiving extensive researches. However, cyclic instability and safety issues hugely confine the commercial applications of traditional liquid LSBs. In this work, for the sake of fully leveraging the high ionic conductivity of polyacrylonitrile while avoiding Li anode “passivation effect” caused by CN group, we prepare double-layer gel polymer electrolytes for quasi-solid-state LSBs. The transition layer composed of polyacrylonitrile, polyethylene oxide and Li1.3Al0.3Ti1.7(PO4)3 (LATP) is located on Li anode side to reduce “passivation effect” triggered by pure polyacrylonitrile. Meanwhile, the high ionic conductivity layer composed of polyacrylonitrile and LATP in contact with cathode can utilize the high intrinsic ionic conductivity of polyacrylonitrile to enhance the rate performance. Furthermore, LATP with higher ionic conductivity embedded in the membrane serves as Li+ transport channels to further increase ionic conductivity. Prominently, the designed double-layer electrolytes exhibit a high Li+ transference number of 0.55 and superior mechanical property. Moreover, stable coulombic efficiency of 99.6–100.0% over 100 cycles and good capacity retention of 79.0% after 100 cycles at 0.1C can be achieved. Our newly designed double-layer electrolytes with multiple functions exhibit potential applications in safer LSBs.