Stabilizing the cathode–electrolyte interphase and enhancing Na+ kinetics by a boron-based anion receptor additive†

Layered metal oxides (NaNi_1/3Fe_1/3Mn_1/3O₂, NFM) hold tremendous commercial potential within the domain of sodium-ion batteries. However, the irreversible phase transitions and interfacial side reactions result in the degradation of cycling performance and poor rate performance, which poses significant obstacles to their commercialization. Herein, tris(2,2,2-trifluoroethyl)borate (TTFEB) is applied as an electrolyte additive to boost the interface stability of the NFM cathode. As an anion acceptor, TTFEB exhibits strong interaction with ClO₄⁻, and the TTFEB–ClO₄⁻ complex accumulates on the surface of NFM during the charging process and decomposes to form a thin and stable cathode–electrolyte interface (CEI), thereby improving interface stability. Meanwhile, the strong interaction between TTFEB and ClO₄⁻ promotes the dissociation of NaClO₄, thereby facilitating the transfer and diffusion of Na⁺ and improving the rate performance of NFM. Consequently, after 200 cycles at 1C, the NFM||Na cell using the 2%TTFEB-containing electrolyte exhibits a superior capacity retention (83.63%) compared to the cell with the baseline electrolyte (73.04%). Moreover, after 400 cycles at 5C, the capacity retention of the cell with the 2%TTFEB-containing electrolyte is 13.02% higher than that with the baseline electrolyte. This study offers a new idea for enhancing the stability of the cathode–electrolyte interface through the utilization of electrolyte additives.