Active fluorobenzene diluent regulated tetraglyme electrolyte enabling high-performance Li metal batteries

Electrolytes with superior compatibility with Li metal anodes and high-voltage cathodes are crucial for high-voltage Li metal batteries. Herein, tetraglyme (G4) with both high oxidation stability and reduction stability is employed to design localized high concentration electrolyte (G4-FB) regulated by active diluent fluorobenzene (FB) via active diluent-anion synergy strategy. FB possesses high activity for generating LiF and cooperates with anions to construct robust LiF-rich solid electrolyte interphases (SEIs) and cathode-electrolyte interphases (CEIs), effectively enhancing the interfacial stability of Li metal anodes and LiNi_0.8Mn_0.1Co_0.1O₂ (NCM811) cathodes. G4-FB enables high-efficiency (99.7 %), long-term (1439 h) and dendrite-free cycle of Li||Li cells and Li||Cu cells. Parasitic interface reactions and structural damages of NCM811 are significantly suppressed by the robust LiF-rich CEIs. G4-FB markedly boosts the performance of NCM811||Li cells even under harsh conditions, including high voltage (4.5 V), high temperature (60 °C), high cathode loading (3.6 mAh cm⁻²) and thin Li metal anode (50 μm), which display a high capacity retention of 86.3 % after 300 cycles. The powerful diluent effect of FB remarkably decreases viscosity, increases ionic conductivity and enhances wettability of G4-FB. This work presents a promising design strategy of highly efficient electrolytes for Li metal batteries.