Liquid-Phase Synthesis of Sulfide Solid Electrolyte: Achieving Extended Composition Ranges and Minimized Carbon Impurities for All-Solid-State Batteries

Advancements in all-solid-state battery (ASSB) technology, featuring non-flammable inorganic solid electrolytes, are gaining significant traction, mainly due to their promise of increased safety and energy density compared to traditional lithium-ion batteries, which rely on flammable organic liquid electrolytes. A key focus of this evolution towards practical ASSBs is the development of sulfide SEs (SSEs), recognized for their exceptional ionic conductivities (reaching up to ~10^-2 S cm^-1) and their ability to be mechanically sintered. Additionally, the employment of wet-chemical synthesis or processing methods for SSEs unlocks intriguing opportunities for the future advancement of ASSB technologies. However, thus far, the number of viable precursor-solvent combinations for the liquid-phase synthesis of SSEs remains limited, primarily due to the solubility constraints of metal chalcogenide precursors such as MS2 (M = Ge, Sn). This limitation hinders the wet-chemical route for synthesizing metal-inclusive compositions like Li₁₀GeP₂S₁₂. Furthermore, the liquid-phase synthesis of SSEs often leaves significant amounts of organic residues derived from organic solvents, leading to the carbonization issue, which could instigate harmful side reactions or self-discharge when used in ASSB cells.<br/>In this presentation, we report on our recent results in developing liquid-phase synthesis strategies for SSEs that extend the compositional availability while minimizing carbon impurities. By leveraging amine-thiol chemistry, metal sulfide precursors can participate in the liquid-phase synthesis alongside conventional precursors of Li₂S, P₂S₅, and LiX (X = Cl, Br, I). Moreover, we introduce a novel heat treatment method that results in near carbon-free SSE products derived from liquid-phase synthesis. These developments hold promising potential for significantly enhancing the electrochemical performance of ASSBs.<br/> <br/>References<br/>1. J. E. Lee, et al., <i>Adv. Mater. </i><b>2022</b>, <i>34</i>, 2200083.<br/>2. J. Woo, et al., <i>Adv. Energy Mater.</i> <b>2023</b>, <i>13</i>, 2203292.