Salt–solvent synchro-constructed robust electrolyte–electrode interphase for high-voltage lithium metal batteries

Abstract

Pairing a high-voltage nickel-rich cathode with a high-capacity lithium metal anode potentially realizes a battery energy density beyond 500 W h kg⁻¹. However, there is lack of suitable electrolytes that are compatible with both the lithium metal anode and high-voltage cathode. Herein, we report an electrolyte design for high-voltage lithium metal batteries (LMBs) by using lithium difluoro(oxalato)borate salt (LiDFOB) and 1,2-ethylene sulfite solvent (ES) whose oxidation and reduction potentials are close to each other, respectively. This special salt–solvent combination induces a synergistic effect to synchro-construct a thin yet robust inorganic–organic interlocking protective film on both the cathode and anode, which is remarkably different from the conventional protective film that usually shows an inner inorganic–outer organic configuration. With a simple formula of “single salt single solvent” and a dilute salt concentration of 1 M (mol L⁻¹), this electrolyte effectively alleviates various challenges faced by high-voltage LMBs, such as lithium dendrite growth, self-discharge, gas evolution and transition metal dissolution, and achieves the stable operation of an NCM622‖Li full cell (2.5 mA h cm⁻², N/P = 4) at a high voltage up to 4.6 V. The capacity retention reaches ∼90% in 200 cycles with an average coulombic efficiency of 99.5%. In addition, this electrolyte demonstrates high ionic conductivity and stability in a wide temperature range, enabling high-voltage LMBs to charge and discharge at temperatures from −30 to 60 °C.