Multifunctional electrolyte additive for high power lithium metal batteries at ultra-low temperatures

Ultra-low temperature lithium metal batteries face significant challenges, particularly sluggish ion transport and uncontrolled lithium dendrite formation, especially under high power. An ideal electrolyte requires high carrier ion concentration, low viscosity, rapid desolvation, and stable interfaces. However, harmonizing these attributes remains a formidable task. Here, we designed and synthesized a multifunctional additive, perfluoroalkylsulfonyl quaternary ammonium nitrate (PQA-NO₃), which features both cationic (PQA⁺) and anionic (NO₃^-) components. PQA⁺ reacts in situ with lithium metal to form an inorganic-rich solid-electrolyte interphase (SEI) that enhances Li⁺ transport through the SEI film. NO₃^- creates an anion-rich, solvent-poor solvation structure, improving oxidation stability at the cathode/electrolyte interface and reducing Li⁺-solvent interactions. This allows ether-based electrolytes to achieve high voltage tolerance, increased ionic conductivity, and lower desolvation energy barriers. The Li (40 µm)||NMC811 (3 mAh cm^-2) cells with the developed electrolyte exhibited stable cycling at -60 ℃ and a 450 Wh kg^-1 pouch cell retained 48.1% capacity at -85 ℃, achieving a remarkable energy density of 171.8 Wh kg^-1. Additionally, the pouch cell demonstrated a high discharge rate of 3.0 C at -50 ℃, reaching a power density of 938.5 W kg^-1, highlighting the electrolyte's potential for high-rate lithium metal batteries in extreme low-temperature environments.