Advancing sulfide solid electrolytes via green Li2S synthesis

We present a potentially eco-friendly, cost-efficient strategy for synthesizing high-purity Li2S, a key precursor for sulfide-based solid electrolytes. While these electrolytes surpass conventional organic counterparts in both safety and performance, their widespread application is hindered by the high cost of Li2S. Here, a solvent-free metathesis route is developed, in which thiourea serves as an S2⁻ donor to sulfurize LiOH, enabling scalable Li2S production (∼100 g per batch) with significantly reduced projected costs. During the process, intermediates (H2NCN, H2O) are transformed into benign gases (CO2, NH3) that spontaneously leave the system, thereby driving Li2S formation without ΔGmix limitations. The as-synthesized Li2S is successfully applied to prepare sulfide-based solid electrolytes such as Li10GeP2S12 and argyrodite-Li5.5PS4.5Cl1.5, achieving laboratory-scale (1 kg) production costs reduction of up to 27.5% and 92.9%, respectively. Furthermore, all-solid-state batteries employing Li5.5PS4.5Cl1.5 demonstrate electrochemical performance comparable to those fabricate with commercial Li2S. This scalable methodology thus may provide a proming pathway to bridge low-cost Li2S synthesis with the practical deployment of sulfide-based solid electrolytes, which may accelerate the commercialization of high-performance all-solid-state batteries. Sulfide solid electrolytes show potential for safer, higher-performance batteries, but costly Li2S precursors hinder commercial adoption. Here, authors develop a scalable, potentially eco-friendly Li2S synthesis method that reduces its production costs, which could facilitate wider deployment of sulfide solid electrolytes.