Breaking the Solubility Limit of LiNO₃ in Carbonate Electrolyte Assisted by BF₃ to Construct a Stable SEI Film for Dendrite-Free Lithium Metal Batteries

Lithium (Li) metal is regarded as a potential candidate for the next generation of lithium secondary batteries, but it has poor cycling stability with the broadly used carbonate-based electrolytes due to the uncontrollable dendritic growth and low Coulombic efficiency (CE). LiNO3 is an effective additive and its limited solubility (<800 ppm) in carbonate-based electrolytes is still a challenge, as reported. Herein, using BF3 (Lewis acid) is proposed to enhance the solubility of LiNO3 in carbonate-based electrolytes. The dissolved NO3- can be involved in the first solvation shell of Li+, reducing the coordination number of PF6- and EC (ethylene carbonate). In addition, the NO3- is proved to be preferentially reduced on Li metal by differential electrochemical mass spectrometry so that the decomposition of PF6- and EC is suppressed. Therefore, a SEI layer containing Li3N can be obtained, which exhibits high lithium-ion conductivity, achieving even and dense Li deposits. Consequently, the CE of Li||Cu cell with BF3/LiNO3 can be increased to 98.07%. Moreover, the capacity retention of Li||LiFePO4 with a low N/P ratio (3:1) is as high as 90% after 300 cycles (approximate to 1500 h). This work paved a new way for incorporating LiNO3 into carbonate-based electrolytes and high-performance lithium metal batteries.