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

Abstract

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. An intensive effort in the development of Li-metal batteries is well underway. Here the authors design a Li salt with an asymmetric molecular structure that distinctly contrasts with conventional salts, enabling high-performance Li-metal batteries with carbonate electrolytes.