Toward High‐Quality Sulfide Solid Electrolytes: A Liquid‐Phase Approach Featured with an Interparticle Coupled Unification Effect

Abstract Sulfide solid electrolytes (SSEs) are highly wanted for solid‐state batteries (SSBs). While their liquid‐phase synthesis is advantageous over their solid‐phase strategy in scalable production, it confronts other challenges, such as low‐purity products, user‐unfriendly solvents, energy‐inefficient solvent removal, and unsatisfactory performance. This article demonstrates that a suspension‐based solvothermal method using single oxygen‐free solvents can solve those problems. Experimental observations and theoretical calculations together show that the basic function of suspension‐treatment is “interparticle‐coupled unification”, that is, even individually insoluble solid precursors can mutually adsorb and amalgamate to generate uniform composites in nonpolar solvents. This anti‐intuitive concept is established when investigating the origins of impurities in SSEs electrolytes made by the conventional tetrahydrofuran‐ethanol method and then searching for new solvents. Its generality is supported by four eligible alkane solvents and four types of SSEs. The electrochemical assessments on the former three SSEs show that they are competitive with their counterparts in the literature. Moreover, the synthesized SSEs presents excellent battery performance, showing great potential for practical applications.