【Frontiers in HaiChuan Chemical Technology】Hydrogen sulfide neutralization method: Playing a key role in the future of lithium sulfide production routes

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Lithium sulfide is an important component of solid-state electrolytes based on sulfides; it influences the ionic conductivity of these solid-state electrolytes and is one of the key factors determining the performance of all-solid-state batteries. It can be regarded as the \"heart\" of solid-state batteries based on sulfides. Lithium sulfide accounts for 77% to 80% of the cost of electrolyte materials in solid-state batteries, and the progress made in reducing its cost directly determines the speed at which such batteries can be brought to market. Currently, the main methods for synthesizing lithium sulfide include ball milling, solvent method, high-temperature and high-pressure method, and hydrogen sulfide neutralization method. Ball milling method: Under an inert atmosphere, elemental sulfur is mixed in proportion with lithium metal and lithium hydride, and then a ball milling reaction is carried out to produce lithium sulfide. This method involves high raw material costs, generates many by-products, and is not suitable for purification. Solvent method: Lithium and lithium compounds are mixed with sulfur and sulfur compounds in organic solvents or liquid ammonia to carry out a reaction for the preparation of lithium sulfide. In this approach, the organic solvents are difficult to recover, and liquid ammonia poses safety concerns. High-temperature and high-pressure method: Under an inert or reducing atmosphere, lithium, lithium compounds, and sulfur or sulfur compounds are combined under high temperature and pressure through reduction or gas-phase reactions to produce lithium sulfide. Lithium sulfide obtained by this method is easy to purify, but it requires high energy consumption, sophisticated equipment, and the reaction conditions are difficult to control. Hydrogen sulfide neutralization method: The raw materials include hydrogen sulfide and lithium hydroxide; a high-temperature reaction produces lithium sulfide and water. This method offers the advantages of high purity and suitability for large-scale production. At present, it is possible to achieve high purity of lithium sulfide at low costs, making the hydrogen sulfide neutralization method the most promising approach. As a key precursor for sulfide solid electrolytes, lithium sulfide accounts for 77%–80% of the cost of electrolyte materials. The current market price for it is as high as 3–4 million yuan per ton, and the process of reducing its cost directly determines the speed at which solid-state batteries can be brought to market.