Anion-diluent synergistic strategy for improved interfacial stability in lithium metal batteries

Recently, high-voltage Li metal batteries (LMBs) have shown great potential as high-energy-density energy storage devices. However, current electrolytes struggle to form stable interfacial films on both the Li anode and high-voltage cathode simultaneously, leading to unsatisfactory cycling stability in high-voltage LMBs. Here, lithium bis(oxalate)borate (LiBOB) with a large π conjugate structure and fluorine-rich hydrofluoroether (HFE) are co-introduced into conventional ether electrolyte to balance dipole-dipole interactions. This results in the formation of an elastic F- and B-O-rich anodic interfacial layer and a robust boron-rich cathode-electrolyte interphase (CEI), leading to superior cycling ability. Consequently, the Li||Cu cell shows an extremely long cycle life of 9500 h under 1 mA cm⁻² and 1 mAh cm⁻², which is the best as reported so far. The Li||LiCoO₂ cells exhibit a superior capacity retention of ∼82.32% under 4.5 V after 160 cycles, with an average CE of > 99.9%. The correspondent Li||NCM811 pouch cells (5 Ah, 400 Wh/kg; 3.3 Ah, 434 Wh/kg) could stably cycle at 0.5 C for 200 cycles and 130 cycles, respectively. This work offers a novel and effective strategy to commercialize ether-based electrolytes for high-energy-density and long-life LMBs.