Stable Cycling Lithium-Sulfur Solid Batteries with Enhanced Li/Li₁₀GeP₂S₁₂ Solid Electrolyte Interface Stability

We herein explore a facile and straightforward approach to enhance the interface stability between the lithium superionic conducting Li₁₀GeP₂S₁₂ (LGPS) solid electrolyte and Li metal by employing ionic liquid such as 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/ N-methyl- N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₃TFSI) as the interface modifier. The results demonstrated the presence of 1 M LiTFSI/PYR₁₃TFSI ionic liquid; the interface stability at the electrode/solid electrolyte (i.e., Li/LGPS) was improved remarkably by forming an in situ solid electrolyte interphase (SEI) layer. As a result, an effectively reduced interfacial resistance from 2021 to 142 Ω cm² and stable Li stripping/plating performance (over 1200 h at 0.038 mA cm^-2 and 1000 h at 0.1 mA cm^-2) were achieved in the Li/LGPS/Li symmetric cells. On this basis, the Li-S solid-state batteries were further architectured with one of the S@C composite [where C is the ketjen black carbon (KBC) or PBX 51-type activated carbon (PBX51C) or multiwalled carbon nanotubes (MCNTs)] cathode and the LGPS solid electrolyte. The batteries with S@KBC electrodes delivered an excellent discharge/charge performance with a high initial discharge capacity of 1017 mA h g^-1 and better stability than those of the batteries with the S@PBX51C and S@MCNTs electrodes. High surface area, unique beneficial pore structure, and better particle dispersion of sulfur in the S@KBC composite facilitate high sulfur utilization and also increase the intimate contact between the electrode and LGPS solid electrolyte during the discharge/charge process.