Anion-dominant coordinated weakly solvating ether electrolyte for silicon anodes

Silicon anodes, with theoretical capacity of 3579 mAh g−1, enable high-energy lithium-ion batteries but suffer from large volume change and unstable solid-electrolyte interphases (SEIs). We design a weakly solvating ether electrolyte—2 M LiFSI in ethylene glycol dibutyl ether (EGDE)—that stabilises micro-Si by tuning Li+ coordination to reduce solvent participation and increase anion accessibility. Operando Raman spectroscopy and molecular-dynamics modelling reveal an anion-dominated solvation structure (CIP + AGG = 78.7 %) that lowers Li+–solvent binding free energy and accelerates desolvation. In this weak-solvation regime, FSI− co-migrates with Li+ and reduces at the anode/electrolyte interface, forming a LiF-rich inorganic SEI with improved chemo-mechanical integrity. EGDE affords weaker Li+–solvent interactions, faster charge-transfer kinetics, and lower desolvation barriers than DME and DGDE, promoting interfacial transport while suppressing side reactions. mSi‖Li half-cells deliver 1512 mAh g−1 with an initial Coulombic efficiency of 80.3 % and sustain >99 % efficiency for 100 cycles. mSi‖NCM811 full cells provide 136.7 mAh g−1 at 0.2 C and show superior life over 50 cycles. This coordination-centric strategy decouples capacity fade from repeated SEI repair, mitigating electrolyte depletion and particle fracture in micro-Si. EGDE offers a fluorine-additive-free route to inorganic-rich SEI formation and guides electrolyte design for next-generation high-energy lithium-ion batteries.