Design of a High-Strength Separator for Lithium Metal Anode-Based Semi-Solid-State Batteries

Abstract Lithium metal anodes face challenges due to lithium dendrite growth and safety risks with liquid electrolytes. To address issues, this study proposes a functional coated separator designed to enhance the mechanical strength of the separator with higher puncture resistance to lithium dendrites and lower the liquid electrolyte-lithium metal anode contact. The separator consists of a polyethylene (PE) base film and two-side coating, alumina (Al2O3) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) on one side, with lithium aluminum titanium phosphate (LATP) and then with polyethylene oxide (PEO) on the other. The separator has exhibited a remarkable performance featuring high puncture strength (480 gf) and excellent electrochemical stability (electrochemical window 5.03 V). It is observed that lithium symmetric cells in semi-solid batteries with this separator stay stable in operation for over 1000 hours (0.2 mA cm-2). LiFePO4||Li cells assembled under lean electrolyte conditions (15 μL mAh-1) deliver discharge specific capacities of 161.9 mAh g-1 at 0.1 C and a capacity retention rate of 87.9% after 120 cycles at 0.5 C. In general, this provides a promising prospect for further application of functionalized coated separators in semi-solid-state lithium batteries with lithium metal anodes.