An artificial interphase enables stable PVDF-based solid-state Li metal batteries

Composite polymer electrolytes (CPEs) have attracted much attention for high energy density solid-state lithium-metal batteries owing to their flexibility, low cost, and easy scale-up. However, the unstable Li/CPE interface is always challengeable for the practical utilization of CPEs. Herein, a polymer interlayer containing K⁺ prepared by ultraviolet (UV)-curing precursor solution is coated on Li surface to stabilize the interface between poly(vinylidene difluoride) (PVDF) composite electrolytes and Li anode. Benefiting from the physical barrier of the interlayer, the continuous decomposition of PVDF is restrained and the intimate contact between electrode and electrolyte is also achieved to reduce the interface impedance. Moreover, the added K⁺ is utilized to further regulate smooth Li deposition. As a consequence, the symmetric Li|Li cell with coated Li demonstrates steady cycling at 0.4 mAh·cm⁻² and a high critical current density of 1 mA·cm⁻². The assembled Li|LiFePO₄ cell presents outstanding cycling stability (capacity retention of 90% after 400 cycles at 1 C) and good rate performance. The associated pouch cell performs impressive flexibility and safety. This work provides a convenient strategy to achieve stable Li/PVDF interface for high-performance PVDF-based solid state Li metal batteries.