Marrying a Non-Flammable Phosphate Solvent with Lithium Nitrate: Novel Electrolyte for Intrinsically Safe and High Performance Lithium Metal Batteries

The formation of Li dendrites and deterioration of the mechanical integrity of Nickel (Ni)-rich cathodes directly hinder the commercialization of high-voltage lithium (Li) metal batteries (LMBs) with Ni-rich cathodes. Herein, a novel electrolyte was tailored by combining triethyl phosphate (TEP) solvent with lithium nitrate (LiNO3) as the main salt and fluoroethylene carbonate (FEC) additive. The preferential electrochemical decomposition of LiNO3 and FEC provides robust and conductive solid/cathode electrolyte interphase (SEI/CEI) layer on the surface of the anode/cathode, which can protect both electrodes effectively during long-term cycling. In this study, non-flammable electrolyte based on TEP solvent is proposed for safe operation. More attractively, LiNO3 is an easily synthesized salt, so the total cost of the fabricated electrolyte can be reduced considerably. Benefiting from the synergetic effect of LiNO3 and FEC, NFE-LiNO3 exhibited outstanding performances in the cells with LiNi0.6Mn0.2Co0.2O2 (Li||NMC622) under high voltage (4.3 V), achieving an extremely high average efficiency of 100% with an exceptional capacity retention of 90% after 250 cycles. Furthermore, significantly enhanced performance using NFE-LiNO3 was also realized with various 4 V class cathode materials in LMBs. These results provide useful insights into the rational design of highly efficient, non-flammable, and low-cost electrolyte for long-lasting high-voltage LMBs.