Solvent-association regulated electrolyte enables high-rate lithium metal batteries at low-temperature

Abstract

To address the challenges of sluggish kinetics and unstable interfaces in lithium metal batteries under high-voltage, low-temperature, and fast-charging conditions, this work proposes a solvent–solvent association regulation strategy. A weakly competitive solvation electrolyte is designed using a ternary solvent system with LiBF₄/LiDFOB dual salts. In the electrolyte, methyl propionate (MP) forms an intermolecular association with methyl trifluoroacetate (MTFA) through δO⁻⋯δH⁺ bonds, weakening their solvation capability, significantly reducing the desolvation energy barrier of lithium ions. Meanwhile, it works synergistically with fluoroethylene carbonate and dual salts to promote the formation of an inorganic-rich and stable interface. Therefore, under the condition of −30 °C, the NCM811||Li cell (2.5–4.5 V) with this electrolyte delivers a discharge capacity of 137 mAh g⁻¹ at 5C (82.5% of that at room temperature) and maintains a high capacity retention rate of 89.26% after 150 cycles at 3C. Furthermore, the NCM811||Li pouch battery (3.3 Ah) exhibits a discharge capacity of 2.21 Ah at −40 °C.