Dual-layer composite solid polymer electrolytes with Janus properties for interface modification of solid state lithium metal batteries

Solid polymer electrolytes are widely applied in lithium metal batteries owing to good flexibility and machinability. However, monolayer polymer electrolyte are difficult to simultaneously satisfy the interfacial contact with the cathode and Li anode. Herein, the dual-layer composite solid polymer electrolyte with polypropylene film (CSPE@PP) are designed to promote the interfacial compatibility between the solid electrolytes and electrodes. The X-ray photoelectron spectroscopy (XPS) results confirm that poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) can react with Li metal to form LiF layer, restraining the Li dendrite growth. Meanwhile, the polyacrylonitrile (PAN) antioxidant layer strengthens the contact stability between the electrolytes and the cathodes. Moreover, the PP film serves as the electrolyte's skeleton and connecting layer, enhancing the ion diffusion and mechanical strength of the solid electrolytes. As a result, the Li||CSPE@PP||Li cell is able to stably cycle over 400 h at 0.1 mA cm-2. The LFP||CSPE@PP||Li solid-state batteries deliver 141.98 mAh g-1 discharge capacity and high retention rate (91.1%) after 100 cycles at 0.1C. This work provides a viable strategy for expanding the application of composite solid polymer electrolyte (CSPE) in lithium metal batteries.