Engineering green and sustainable solvents for scalable wet synthesis of sulfide electrolytes in high-energy-density all-solid-state batteries

Abstract

Argyrodites, Li₆PS₅Cl (LPSCl), are considered one of the most promising solid electrolytes (SEs) for all-solid-state batteries (ASSBs). However, the use of petrochemical-based toxic solvents, such as dimethylformamide and tetrahydrofuran (THF), has limited their commercial applications in the mass production of SEs via liquid-phase synthesis both in the laboratory and industry. Herein, we aim to achieve the scalable production of cost-effective LPSCl-based sulfide SEs with high ionic conductivities (>2 mS cm⁻¹) based on various green and sustainable inert solvents. Our simple liquid-phase synthesis route was designed by using sulfur to form an intermediate polysulfide to completely dissolve precursors in common organic solvents without employing high-energy and high-pressure processes. Metastable polysulfides have high solubility in a broad range of solvents; they offer the use of greener and/or sustainable alternatives. The ASSBs fabricated with the LPSCl SEs using green solvents exhibited excellent electrochemical performance comparable to that of LPSCl wet-synthesized using conventional THF. LPSCl SEs fabricated using monoglyme, which has the most similar solvent properties to those of THF, exhibited the best ionic conductivity and contributed to the high electrochemical performance of ASSBs. The state-of-the-art bulk-type production of sulfide SEs using solution-phase synthesis should ultimately be replaced by green and/or sustainable solvents to reduce chemical-related effects on human health and eliminate environmental pollution. Therefore, this study will be of great interest to those who wish to mass-produce sulfide-based SEs cost-effectively for commercial applications with minimal unnecessary steps.