Steric Selectivity of Isomeric Ether Solvents for Fast-Charging and Low-Temperature SiOx Anodes

SiO_x anodes promise high-energy-density batteries but suffer under fast-charging and low-temperature conditions because of an unstable SiO_x/electrolyte interphase and sluggish Li⁺ transport in the electrolyte. Given the importance of the electrolyte, we propose an isomer-specific steric-selective solvent strategy and screen the optimized solvent. The intricate relationship between solvent structure and electrochemical performance was explored based on two isomeric cyclic ethers with the same molecular formula (C₅H₁₀O): tetrahydropyran and 2-methyltetrahydrofuran (MTHF). The steric hindrance effect induced by −CH₃ in MTHF weakens the coordination between solvent and Li⁺, facilitating the formation of anion-derived solvation structures and a robust inorganic-rich interphase with high mechanical stability. Consequently, the MTHF-based electrolyte enables the LiFePO₄|SiO_x pouch cell with fast-charging capability (70%-capacity retention at 6 C) and low-temperature performance (46%-discharge-capacity retention under −50 °C). This isomeric steric-selective insight links molecular structure to interfacial chemistry and electrochemical performance, guiding electrolyte design for high-energy-density batteries under extreme conditions.