A polysulfide-functionalized separator enables robust long-cycle operation of lithium-metal batteries

Abstract

A separator plays an irreplaceable role in controlling battery safety and lifespan. Polyethylene (PE) and polypropylene (PP) are applied in batteries as separators to block electrons and transport lithium ions, on account of their chemical and mechanical stability. Unfortunately, the poor wettability and thermal stability limit their large-scale applications. Herein, a stable 16 μm PE-based separator was elaborately designed. The PESV composite separator was obtained by impregnating PE into the matrix of polysulfide (PSU) and polyvinylidene fluoride (PVDF). The obtained PESV showed higher porosity and uniform pore distribution with PSU and PVDF filling in the pores of PE. The PE skeleton provided chemical stability, and PSU offered robustness, while PVDF contributed to excellent wettability and thermal stability simultaneously. Thus, the PESV maintained morphology integrity at 150 °C while PE shrank at 60 °C. PESV exhibited a contact angle of 20° while PE was 48°, PESV reached 145 MPa while PE reached only 78 MPa. The robust PSU enabled the PESV composite separator with stable and long-term operation in the Li/Li battery, without obvious dendrites for nearly 1000 h, while the Li/Li battery with PE failed to handle it after 400 h at 0.5 mA cm⁻². Meanwhile, the LFP/Li batteries with the PESV reached a discharge capacity of 91 mA h g⁻¹, which retained 63% after 1000 cycles at 1C (1.28 mA cm⁻²) with a mass loading of 4 mg cm⁻², demonstrating the stable cycling of LMBs with the PESV composite separator.