Electrolyte/electrode interphase regulation with methylthiolation ionic liquids for high-voltage quasi-solid-state Li metal batteries.

Li, Jin; Chen, Junjie; Xu, Xiaosa; Wang, Zhenyu; Guo, Zixiao; Lin, Pengzhu; Sun, Jing; Huang, Baoling et al. · Sci Adv · 2025

basic_science · Level V

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Abstract

Quasi-solid-state lithium metal batteries (QSSLMBs) are hindered by interfacial instability at high-voltage cathodes and uncontrolled lithium dendrite growth at the anode, limiting their cycling life and energy density. To overcome these challenges, we have developed a piperidine-based ionic liquid (IL) additive featuring a methylthiolation cationic segment that stabilizes the interphase of layered oxide cathodes and lithium anodes under fast charging and high-voltage conditions. These ILs preferentially oxidize to form a robust cathode-electrolyte interphase with LiF and sulfide species, which effectively suppresses dissolution of transition metal and enhances interfacial ion transport. Simultaneously, the IL-derived diverse inorganic species composite interphase at the anode improves mechanical strength and inhibits lithium dendrite growth. The resulting quasi-solid-state electrolyte demonstrates stable operation at a high voltage of 4.5 V, high mass loading of 21.6 mg cm<sup>-2</sup>, high-energy density of 407 Wh kg<sup>-1</sup>, and broad temperature range from -20° to 60°C, advancing the practical application of QSSLMBs.