Designing an asymmetric ether-like lithium salt to enable fast-cycling high-energy lithium metal batteries

Conventional carbonate-based electrolytes with high corrosion towards Li metal result in massive dendrite growth and limited cycling life, particularly true for practical Li-metal batteries with high cathode loading (>3.5 mAh cm−2). Herein we design an asymmetric Li salt, lithium 1,1,1-trifluoro-N-[2-[2-(2-methoxyethoxy)ethoxy)]ethyl] methanesulfonamide (LiFEA) that possesses a pseudo-crown ether-like, folded molecular geometry. It enables carbonate electrolytes with a large apparent donor number and Li+ transference number and drives a self-cleaning mechanism for solid–electrolyte interphases, enhancing compatibility with Li-metal anodes even at high current densities. LiFEA-based carbonate electrolytes notably improved fast-cycling performances of Li | |NCM811 cells. Pouch cells of 310 Wh kg−1 achieved ~410 W kg−1 power density at the discharging current density of 6.59 mA cm−2. Under fast-cycling conditions (charging: 1.46 mA cm−2, discharging: 3.66 mA cm−2), pouch cells maintained 81% capacity after 100 cycles. Our work provides insights into the interplay between the molecular structure of Li salts, their physicochemical properties and electrochemical performances.