Interfacial optimization between cathode and 20 μm-thickness solid electrolyte membrane via in-situ polymerization for lithium metal batteries

Solid electrolyte membranes face a huge challenge in achieving satisfactory interfacial contact with electrodes, which severely impairs the rate performance and cycle life of solid-state lithium batteries. In this work, we fabricated an ultrathin solid polymer electrolyte (SPE) membrane, and based on it we demonstrated the interfacial contact optimization strategy by in-situ polymerization. The free-stranding PVDF-HFP-LiTFSI membrane with a thickness of 20 mu m shows an ionic conductivity of 1.2 x 10-4 S cm- 1 at room temperature. The poly (ethylene glycol) diacrylate-based in-situ polymerized electrolyte tightly connects the cathode and the SPE membrane, decreasing the interfacial resistance from 9380 Cd cm2 to 1100 Cd cm2. Compared with the traditional method employing liquid electrolyte for interfacial wetting, extended electrochemical window (4.6 V) and much improved thermal stability are obtained. Full cell employing LiFePO4 cathode and lithium metal anode shows an initial capacity of 138.9 mAh g-1 under a charge/discharge rate of 0.5C (85 mA g-1) at 60 degrees C, with a capacity retention ratio of 84.9% and a high average Coulombic efficiency (98.7%) after 300 cycles, remarkably better than those of its liquid electrolyte-used counterpart. Our work demonstrates that the application of in-situ polymerization into interfacial contact improvement between SPE and cathode possesses wide application prospects.