Nonafluorobutane‐1‐Sulfonic Acid Induced Local High Concentration Additive Interface for Robust SEI Formation of High‐Voltage (5 V‐Class) Lithium Metal Batteries

Abstract To optimize anode and cathode degradation issues in high‐voltage (5 V‐class) lithium metal batteries (LMBs), robust solid–electrolyte interfaces (SEI) on the surface of both anode and cathode are highly desired. Here, a nonafluorobutane‐1‐sulfonic acid (NFSA) additive is introduced to assist in the formation of the more stable and robust SEI to protect both anode and cathode. Typically, local high concentrations of lithium nonafluorobutane‐1‐sulfonate (NFSALi) and nonafluorobutane‐1‐sulfonate anion (NFSA⁻) could be achieved at the surface of anode and cathode respectively, through spontaneous chemical processes. The lowest unoccupied molecular orbital energy of NFSALi is lower and the highest occupied molecular orbital (energy of NFSA⁻ is higher than electrolyte solvents. Thus, conformal and dense SEI passivation films are generated on the surface of both anode and cathode derived from electrochemical decomposition of NFSALi and NFSA⁻, respectively. Consequently, stable operation of Li metal anode and high‐voltage cathode are realized. The LiNi_0.5Mn_1.5O₄(LNMO)//Li LMBs with NFSA‐containing electrolyte show great cycling stability with 93% capacity retention after 400 cycles and more stable Coulombic efficiency. This work specifies the double functions of NFSA as an interfacial layer forming additive to solve the degradation problems of high‐voltage (5 V‐class) LMBs, enabling high‐energy LMBs with significantly improved battery performance.