Multi-dentate, weakly coordinating co-solvents enable balanced ion dissociation/desolvation kinetics for cryogenic lithium metal batteries

Abstract

The trade-off between rapid Li⁺ transport in the bulk electrolyte and facile desolvation at the electrode interface poses a fundamental challenge for lithium metal batteries (LMBs) operating at subzero temperatures. Herein, we present a synergistic solvation engineering strategy that reconciles this dichotomy by pairing a multidentate solvent (trimethyl orthoformate, TMM) with a weakly coordinating co-solvent (1,3-dioxolane, DOL), further reinforced by LiNO₃ as an anion-participating additive. This formulation deliberately shifts the solvation equilibrium from a solvent-separated ion pair (SSIP)-dominated state toward a co-dominant SSIP/contact ion pair (CIP) configuration. The resulting electrolyte simultaneously achieves enhanced salt dissociation, reduced Li⁺–solvent binding strength, and preferential anion-derived inorganic-rich solid-electrolyte interphase (SEI) formation. Consequently, Li∥LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cells exhibit remarkable low-temperature performance: discharge capacities of 149.22 mAh g⁻¹ at −20 °C and 103.68 mAh g⁻¹ at −40 °C, with capacity retention values of 83% and 58% relative to those at room temperature, respectively. Notably, 83.9% capacity retention is achieved after 500 cycles at −20 °C. This work establishes a generalizable design principle—decoupling ion transport from desolvation kinetics via targeted solvation structure modulation—paving the way for extreme-environment energy storage.