Anion–Diluent Pairing for Stable High-Energy Li Metal Batteries

Rechargeable Li metal batteries (LMBs) have attracted wide attention as promising candidates for the next generation of energy-storage systems. However, limited Coulombic efficiency and unregulated dendrite growth restrict its application. Here, we report a kind of electrolyte by introducing fluorinated aromatic diluents into high-concentration electrolytes (HCEs). Unlike other localized HCEs, the fluorinated aromatic diluents pairing with anions promote the formation of a homogeneous and robust solid–electrolyte interphase (SEI), which endows Li metal with an ultrahigh Coulombic efficiency of ∼99.8%. The Li||LiNi0.8Co0.1Mn0.1O2 battery holds a capacity retention of >80% over 260 cycles even with a thin Li anode (20 μm) and a high cathode loading (3.5 mAh cm–2). A 1.8 Ah Li||NMC811 pouch cell with a lean electrolyte delivers an energy density of 340 Wh kg–1 and a stable cycling life over 200 cycles. The designed electrolytes, which benefit from the synergetic effects of anions and diluents on the SEI, pave the way for the next-generation LMBs.