Breaking Aggregation State to Achieve Low-Temperature Fast Charging of Lithium Metal Batteries

Abstract

Insufficient ionic conductivity and elevated desolvation energy barrier of electrolytes limit the low-temperature applications of lithium metal batteries (LMBs). Weakly solvating electrolytes (WSEs), with limited lithium salt dissociation capability, are prone to desolvate and drive anion-rich aggregates (AGGs). However, significant AGGs result in increased viscosity and low ionic mobility, contributing to battery failure at low temperatures (≤−20 °C). Here, we propose and achieve a transformation of WSEs’ solvation structures from AGGs to contact ion pairs (CIPs) through modulating the overall solvation capability, thereby achieving the balance between weak Li⁺- solvent interactions and desired ion migration kinetics. Remarkably, CIPs-dominated electrolyte shows a ten-fold increase in ionic conductivity compared to conventional WSEs. The Li||LiFePO₄ (LFP) battery achieves more than 1400 cycles with 86.9 % capacity retention at 5 C. The practical 1.2 Ah LFP pouch cell delivered 69 % of the capacity at 25 °C when cycled at −40 °C. This strategy for solvation structure transformation in WSEs provides a novel approach for the development of electrolytes for low-temperature batteries.