A functional additive to in-situ construct stable cathode and anode interfaces for all-solid-state lithium-sulfur batteries

All-solid-state lithium-sulfur batteries (ALSBs) using poly(ethylene oxide) (PEO)-based composite solid-state electrolytes (CSEs) are regarded as one of potential high energy storage devices; however, they still face two core problems of polysulfide shuttle and lithium dendrite during long cycle. Herein, based on a passive-type strategy, magnesium bis(trifluoromethylsulphonyl)imide [Mg(TFSI)₂] as a novel functional additive of the PEO-Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (PEO-LLZTO)-based CSE, has been proved to be successful on both retarding polysulfide species shuttle and stabilizing lithium anode. Study results show that magnesium polysulfide precipitate, formed on the interface between the S/C cathode and CSE, can hinder the shuttle of diffluent lithium polysulfide; and meanwhile, a robust Li_xMg layer generated on the surface of lithium anode can suppress the formation of dendrite. As a consequence, the Mg(TFSI)₂ additive-functionalized PEO-LLZTO CSE obviously prompts a critical current density up to 1.0 mA cm⁻² from 0.6 mA cm⁻² of the sole PEO-LLZTO CSE, and maintains very stable cycling over 500 h at 0.2 mA cm⁻² for a symmetric cell. Furthermore, the ALSB with the Mg(TFSI)₂ additive-functionalized PEO-LLZTO CSE delivers robust cycle performances, with specific capacities of 877 mAh g⁻¹ at 0.1C (1C = 1675 mA g⁻¹) after 50 cycles (capacity retention ratio of 100 %) and 331 mAh g⁻¹ at 0.5C over 300 cycles (capacity retention ratio of 94.1 %) under 50 °C. This work provides a realistic reference in designing novel additives to ameliorate the electrode–electrolyte interfaces for stabilizing ALSB.