AbstractEngineering liquid electrolytes for lithium (Li)-metal electrodes has been used to control the morphology of deposited Li in Li-metal batteries (LMBs). However, the Li corrosion problem remains unresolved, hindering the design of lean electrolytes for practical LMBs, which require the electrolyte/capacity (E/C) ratio to be 2 g Ah⁻¹ or lower. Here we report a borate–pyran-based electrolyte to address the chronic Li-corrosion problem. We discovered that the borate–pyran electrolyte transforms large LiF crystallites in the solid–electrolyte interphase into fine crystalline or glassy LiF, which enhances the passivity of the Li/electrolyte interface by minimizing the permeation of electrolyte molecules into the solid–electrolyte interphase. LMBs assembled with the borate–pyran electrolyte, a high-nickel layered oxide cathode (3.83 mAh cm⁻²) and thin lithium (20 μm) delivered a high initial full-cell-level energy density (>400 Wh kg⁻¹) and operated for 400 cycles with 70% capacity retention at an E/C ratio of 1.92 g Ah⁻¹, 350 cycles with 73% capacity retention at 1.24 g Ah⁻¹ and 200 cycles with 85% retention at 0.96 g Ah⁻¹.