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

Abstract

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 (≈1500 h). This work paved a new way for incorporating LiNO3 into carbonate‐based electrolytes and high‐performance lithium metal batteries.

Behavior of NO3−-Based Electrolyte Additive in Lithium Metal Batteries

“…Figure 10k shows that the solubility of LiNO3 with CsF is improved. Solubilizers that use a similar mechanism to improve the solubility of N additives include BF3 [103,104], tris(pentafluorophenyl)borane (TPFPB) [105], and tin(II) [106]. In addition, there are some strategies using a binary electrolyte that facilitate the dissolution of LiNO 3 .…”