Stable Li Metal Anode with “Ion–Solvent-Coordinated” Nonflammable Electrolyte for Safe Li Metal Batteries

Li metal batteries have recently attracted extensive attention due to the pursuit of high-energy-density batteries for electric vehicles. However, safety and low cycling Coulombic efficiency (CCE) hinder the development of high-energy Li metal secondary batteries due to the high reactivity of Li metal with present electrolytes. Here, we investigate the reductive stability of nonflammable electrolytes with a wide salt to solvent ratio range and demonstrate that an ion–solvent-coordinated (ISC) nonflammable electrolyte–lithium bis­(fluorosulfonyl)­imide (LiFSI)-triethylphosphate (TEP) enables dendrite-free Li metal plating/stripping on the Cu electrode with a high CCE of 99.3% up to 350 cycles. Understanding of the fundamental electrochemistry tells us that the decrease of solvent activity in ISC electrolyte can improve the reductive stability of the solvent on Li metal anodes. The fundamental concept of ISC electrolyte developed in this work provides new perspectives for the development of highly stable and safe Li metal batteries.