Thermoresponsive solid electrolyte interphase enables safe lithium-sulfur batteries with high energy density

The high-activity lithium metal anode limits the practical application of lithium-sulfur batteries in terms of both electrochemical performance and thermal safety. Solid electrolyte interphase (SEI), as a physical barrier between the lithium anode and the electrolyte, plays a crucial role in electrochemically and thermally stable lithium-sulfur batteries. Herein, safe lithium-sulfur batteries with a high energy density are realized by ingeniously designing a smart thermoresponsive SEI. Under normal working conditions, a lithium iodide additive in the electrolyte accelerates the de-solvation process and simultaneously participates in the construction of highly conductive SEI, which promotes rapid transport of lithium ions and uniform deposition of lithium metal. Enhanced electrochemical stability of lithium sulfur batteries can be achieved with capacity retentions of coin cells (4 mA h cm⁻² cathode loading) and 523 W h kg⁻¹ pouch cells (5.9 A h) of 78% after 160 cycles and 73% after 20 cycles, respectively. Once battery abuse and temperature increase occur, a dense antiperovskite layer is self-assembled on the lithium surface by the chemical reactions between lithium iodide, lithium polysulfide and lithium oxide in the SEI at elevated temperatures. The formed thermally stable inorganic antiperovskite can greatly inhibit exothermic reactions, thereby significantly increasing the thermal-runaway onset-temperature of the cycled pouch cells from 116.0 to 162.3 °C. This strategy provides novel insights to simultaneously enhance the safety performance and lifespan of rechargeable batteries.