Cosolvent-Regulated Weakly Solvating Locally Concentrated Ionic Liquid Electrolyte for Long-Life Lithium Metal...

Lithium metal batteries (LMBs) are attractive next-generation high-energy-density systems, but their operation at low temperatures is hindered by sluggish ion transport and unstable interfaces, which trigger dendrite formation and poor Coulombic efficiency. Herein, we introduce monofluorobenzene (FB) as the weakly solvated cosolvent to modulate the liquidity and microstructure of locally concentrated ionic liquid electrolytes to address these challenges. The weak interaction between FB and Li⁺ as well as organic cations not only weakens the strong coordination of Li⁺-anion but also loosens the dense ionic aggregation structure, enabling fast Li⁺ transport in both the bulk and interface. Simultaneously, it drives preferential anion decomposition at the interface, yielding a robust inorganic-rich solid electrolyte interphase. The optimized electrolyte enables stable lithium plating/stripping for 4000 h with low overpotential and achieves outstanding cycling performance in Li||NCM93 cells, maintaining stable cycling for over 500 cycles at -20°C. This work establishes a practical electrolyte design strategy for enabling long-cycling, low-temperature LMBs.