Mechano-chemical solution process for Li3PS4 solid electrolyte using dibromomethane for enhanced conductivity and cyclability in all-solid-state batteries

Increasing conductivity and stability is one of the essential and ultimate goals for electrolyte research. For sulfide solid-state electrolytes (SSEs), elemental doping is often suggested for this purpose. A typical doping method for sulfide SSE is an energy intensive and non-uniform solid-state reaction, because most solvents react with sulfide SSEs. Here, we have demonstrated that highly efficient Br-doping into lithium thiophosphate Li3PS4 (LPS) can be achieved through a solution-based strategy using dibromomethane (DBM) as Br-source and solvent in a ballmilling process. In this "mechano-chemical" process, simultaneous pulverization of large LPS particles and Brdoping occur, achieving remarkably improved Li+ ion conductivity (1.3 mS cm-1) which is eight times higher than that of the pristine LPS at only 1.14 at. % Br doping. This conductivity is one of the highest for LPS SSE, especially at this low doping level. The LPS to DBM ratio critically affects the efficiency of these chemical and physical modifications. In all-solid-state lithium-metal-batteries, the modified LPS exhibited exceptional cycling stability with reduced overpotential. The Li-Li symmetric cell demonstrated extremely stable Li deposition and stripping for over 1350 h, and the full cell with the Li anode and Li[Ni0.8Co0.1Mn0.1]O2 cathode retained 83 % of its initial capacity after 100 cycles. With possible application toward the slurry fabrication of LPS SSEs, the proposed approach provides a new and effective strategy for fabricating high-performance sulfide SSEs for largescale applications.