Recent Advances in Lithium Sulfide Preparation Routes: Thermodynamics, Phase Behavior, and Scale-Up Challenges

Abstract

The scalable and low-cost preparation of Li2S with application-appropriate purity and particle characteristics remains a major bottleneck restricting the industrialization of next-generation solid-state and lithium–sulfur (Li–S) batteries. This paper systematically reviews the basic properties, application value, and mainstream preparation routes of Li2S, focusing on three core synthesis methods: the H2S sulfidation route, the metathesis route, and the Li2SO4 reduction route, as well as supplementary processes such as the solvent-free thiourea method, mechanochemical synthesis, and plasma-assisted direct Li–S reaction. The thermodynamic driving forces, phase behavior, mass transfer characteristics, impurity sources, byproduct separation, and engineering scale-up challenges of each route are analyzed and compared. This review points out the future development directions of Li2S preparation technology, including developing low-hazard and solvent-lean synthesis systems, establishing standardized impurity detection and purity evaluation methods, strengthening the integrated design of reaction–separation–recycling, and customizing Li2S morphology and composite structures according to application scenarios. This review is expected to provide a quantitative basis for the large-scale, low-cost, and stable preparation of application-tailored Li2S for sulfide solid-state electrolytes and Li–S batteries.