Tuning steric hindrance of cyclic ether electrolytes enables high-voltage lithium metal batteries

Ether-based electrolytes are known for their high stability with lithium metal anodes (LMAs), but they often exhibit poor high-voltage stability. Structural optimization of ether-based solvent molecules has been proven to effectively broaden the electrochemical window of these electrolytes, yet the optimization rules within cyclic ethers remain unclear. Herein, we investigate the impact of methyl substitution positions on the molecular properties of 1,3-dioxolane (DOL), a commonly used cyclic ether. The results show that the introduction of methyl groups can effectively inhibit the ring-opening polymerization of DOL. Besides, 4-methyl-1,3-dioxolane (4-Me DOL), with larger steric hindrance compared to 2-methyl-1,3-dioxolane (2-Me DOL), exhibits weaker solvation ability, favoring the formation of anion-rich inner solvation sheath layers and anion-derived interfaces. Even at conventional concentrations, 1 M LiFSI in 4-Me DOL (LiFSI/4-Me DOL) electrolyte demonstrates good LMA stability and an expanded electrochemical window up to 4.6 V. The Li-LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cell using LiFSI/4-Me DOL could stably cycle over 300 times. This work reveals a new design principle for solvent molecules.