Propelling lithium transport kinetics and inhibiting Al corrosion by high-coordination-strength anion for low-temperature lithium-metal batteries

The deployment of high-voltage lithium metal batteries (LMBs) under low-temperature conditions holds considerable importance for the advancement of fast charging technologies. Nevertheless, such deployment necessitates electrolyte designs with contradictory requirements, most notably in the realm of solvation structure. Principally, the lithium salts with weakly coordinated anions facilitate the rapid Li⁺ transport due to large population of solvent separated ion pairs (SSIPs) and low energy of de-anion process at low temperatures. However, such salts corrode aluminum (Al) foil and worsen the battery stability at high voltages. Herein, this fundamental conflict has been unified through surface electric field and interface compositions. The strongly coordinated anions exhibit higher negative charge density due to its high electron constraining capability, as demonstrated with electron localization function (ELF) and nuclear magnetic resonance (NMR). Such characteristic drives them to exhibit faster migration towards the against direction of Li⁺ under un electric field and hence facilitate the Li⁺ de-coordination. Meanwhile, the X-ray photoelectron spectroscopy (XPS) demonstrated that the strongly coordinated anions benefit the formation of Li₂CO₃ and Li₂O in solid electrolyte interface (SEI), which exerts a stronger attraction on the Li⁺ of solvation structure, thereby assisting the Li⁺ de-coordination process. The contradiction between Li⁺ transport kinetics and Al corrosion can be unified with high-coordination-strength anion at low-temperature. This formulated electrolyte enables stable operation of high-voltage LMBs even at low temperatures, demonstrating a practical guiding principle for extreme-condition batteries.