Multi-dentate, Weakly Coordinating Co-solvents Enabling 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 LiNO 3 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 0.8 Co 0.1 Mn 0.1 O 2 (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 retentions of 83% and 58% relative to 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.