Bidirectional Interphase Modulation of Phosphate Electrolyte Enables Intrinsic Safety and Superior Stability for High-Voltage Lithium–Metal Batteries

Developing advanced high voltage lithium–metal batteries (LMBs) with superior stability and intrinsic safety is of great significance for practical applications. However, the easy flammability of conventional carbonate solvents and inferior compatibility of commercial electrolytes for both highly reactive Li anodes and high-voltage cathodes severely hinder the implementation process. Hence, we rationally designed an intrinsically nonflammable and low-cost phosphate electrolyte toward stable high-voltage LMBs by bidirectionally modulating the interphases. Benefiting from the synergistic regulation of LiNO3 and DME dual-additives in the 1.5 M LiTFSI/Triethyl phosphate electrolyte, thin, dense and robust electrodes/electrolyte interphases were well constructed simultaneously on the surfaces of Li anode and Ni-rich cathode, dramatically improving the stability and compatibility between electrodes and electrolyte. Consequently, boosted kinetic and high Coulombic efficiency of 98.6% for Li metal plating/stripping over 400 cycles and superior cycling stability of exceeding 4,000 h in Li symmetric cell is achieved. More importantly, the Li∥LiNi0.6Mn0.2Co0.2O2 cell assembled with a thin Li anode and high mass-loading cathode at a high cutoff voltage of 4.6 V retains a 98.4% capacity retention after 500 cycles at 1C. This work affords a promising strategy to develop nonflammable electrolytes enabling the high safety, good cyclability, and low cost of high-energy LMBs.