Construction of flexible asymmetric composite polymer electrolytes for high-voltage lithium metal batteries with superior performance

The primary obstacle hindering the application of composite solid electrolytes lies in the varying demands posed by the Li metal anode and the cathode, which needs to be capable of suppressing dendrite growth and resisting high voltage simultaneously. In this work, a new asymmetric composite solid-state electrolyte prepared via electrospinning and in-situ polymerization is proposed to address these shortcomings. In this bilayer architecture, polyacrylonitrile (PAN) layer of high-voltage tolerance, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) layer of robust mechanical strength and good compatibility towards Li-anode are constructed, and metal-organic-frameworks (MOFs) are pre-embedded within both layers. The unique design provides a wide electrochemical stability window meanwhile ensures uniform lithium deposition. Remarkably, it exhibits a superior lithium utilization of 41 mAh cm −2 using a lean polymer electrolyte precursor and a high critical current density of 2.2 mA cm −2 with a thickness of 40 μm. Beneficial from the formation of a self-adjustable gradient solid electrolyte interphase in the Li/PVDF-HFP interface, the asymmetric electrolyte endows Li||Li and Li||NCM811 cells with excellent cycling stability. Moreover, the solid-state pouch cell exhibits reliable operation under extreme conditions. This work provides inspiration for the design and fabrication of composite solid electrolytes for next-generation high-voltage Li metal batteries. • PPH-SSE exhibits stability towards cathode and lithium metal anode simultaneously. • A high lithium utilization of 41 mAh cm −2 in Li||Li symmetrical cell is achieved. • PPH-SSE is thin yet possesses a high critical current density (2.2 mAh cm −2 ). • A self-adjustable gradient SEI with LiF-rich inner and Li 3 N-rich surface is formed. • The cell using PPH-SSE delivers 85 % retention after 300 cycles at room temperature.