Research Progress on Lithium Sulfide Synthesis: A Review

All-solid-state batteries (ASSBs) are regarded as the core direction of the next generation of energy storage technology, with their commercialization time schedule being specifically listed out officially. However, the promising future of ASSBs is highly dependent on the high-efficiency synthesis of lithium sulfide (Li₂S), which is a critical raw material for fabricating solid electrolytes. In fact, Li₂S is also a competitive cathode material for lithium–sulfur batteries due to its high theoretical specific capacity (1167 mAh/g). Unlike previous reports that focus on a single reaction path or experimental details, this review systematically summarizes Li₂S synthesis strategies from a new dimension of reaction medium (liquid phase, solid–solid, gas–solid) and constructs a six-dimensional radar evaluation system based on economic, technical, and environmental impacts. The contents can hopefully provide a comprehensive understanding of synthesizing critical Li₂S raw materials for energy storage, especially for ASSBs.