Excellent Stable Cycle Performance of Polyethylene Oxide-Based 3D Solid Dual-Salt Composite Electrolyte with Porous Polyimide Thin Films Host

Polyethylene oxide composite electrolytes are widely used in lithium-ion batteries because of their excellent moldability, good flexibility, and favorable chemical compatibility. However, they still suffer from low ionic conductivity and weak mechanical strength. Herein, a 3D nanofiber-reinforced dual-salt composite solid electrolyte (PI@PCB) is synthesized. Benefiting from the support of the porous polyimide films and the addition of lithium bis(oxalate)borate, the obtained PI@PCB electrolyte exhibits high mechanical strength, good thermal stability, excellent electrochemical stability, and a high lithium ion transference number (0.70). In addition, the assembled Li/PI@PCB/Li cell shows the lowest overpotential of 200 mV at the initial cycling stage and increases to 246 mV slightly after 1500 h. The capacity retention rate of Li/PI@PCB/LFP battery is about 88.3% after 500 cycles at 60 °C.