Regulating Li-Ion Transport via Solvent and Ion Clustering Using Ternary Salts in Nonfluorinated Solvents for...

Electrolyte engineering strategies that exploit nonfluorinated solvents at low electrolyte concentrations are crucial for enabling next-generation high-performance and safer batteries, including zero-excess lithium metal batteries (ZELMBs). We demonstrate such a protocol using ether-based solvents, wherein the coordination of Li⁺ by distinct anions within the solvation shell enhances the Li⁺ transference number and stabilizes interfacial passivation. The tendency of solvents to form clusters facilitates Li⁺ desolvation prior to plating, enhancing ZELMB cycling performance to approximately 80%. At a comparatively low concentration (1.4 M) of salts in nonfluorinated solvents, the electrolyte stabilizes ZELMB performance with an average Coulombic efficiency of ∼98%. A cell employing an NMC811 cathode and a Cu current collector can sustain >90 cycles with >50% capacity retention. Spectroscopic and molecular dynamics analyses reveal cooperative solvent-anion clustering that drives the transition from solvent-dominated to mixed ion-solvent Li⁺ coordination, underpinning enhanced transport. This study establishes a pathway for designing low-cost, fluorine-free solvent-based electrolytes for metal batteries of extended cyclability.