Watermelon-like solvation structure enables ultra-low-concentration electrolytes for high-rate and low-temperature lithium metal batteries.

Abstract

Electrolyte engineering is crucial for developing high-rate and low-temperature lithium-metal batteries. Conventional carbonate-based electrolytes have achieved broad success in commercial batteries, but their high freezing point, high viscosity, and strong Li+ solvation ability severely limit Li+ transport and interfacial kinetics under high-rate and low-temperature conditions. Herein, we propose an ultra-low-concentration electrolyte featuring a co-solvation shell and a "watermelon-like" solvation structure. In this electrolyte, localized Li+-centered solvation clusters are spatially isolated by a low-viscosity diluent matrix, which improves ionic transport at low temperatures. Meanwhile, the anion- and additive-co-dominated solvation sheath promotes the formation of highly ion-conductive and stable solid electrolyte interphase and cathode electrolyte interphase layers. As a result, Li||LiFePO4 cells using this ultra-low-concentration electrolyte deliver a high discharge capacity of 122.9 mAh g-1 at 5C and retain 77.75% of their capacity after 3000 cycles. Moreover, the cells maintain 98.65% capacity retention after 100 cycles at -30 °C. This work provides a feasible electrolyte design strategy for next-generation lithium-metal batteries with high-rate capability and low-temperature performance.