One-step NH₄F Treatment for Stabilizing Mn³⁺ in Lithium-Rich Manganese-Based Cathodes

Lithium-ion batteries have been widely used in electric vehicles and energy storage facilities as the main source of high-energy storage devices, and with the development of science and technology, higher capacity demands have been raised. In lithium-rich manganese-based cathode materials, trivalent manganese ions (Mn³⁺), as electrochemically active species, contribute to the specific capacity through their own redox reactions. However, it has the disadvantage of instability in layered structures, which can easily lead to dissolution and Jahn-Teller distortion (J-T distortion), resulting in poor material cycling stability. Based on the structural induction effect of ammonium ions (NH₄⁺) on spinel formation and the fluorination effect of fluoride ions (F^-), we designed an experiment to modify lithium-rich manganese-based materials via a one-step ammonium fluoride (NH₄F) treatment, which enabled the in situ formation of a spinel structure on the material surface. This work stabilized Mn³⁺ ions through spinel structure, which can effectively improve the capacity of lithium rich manganese-based electrode materials while stabilizing the cycle performance of electrode materials. The results show that the Mn³⁺ content in the spinel phase of the modified material is greatly increased, the negative effect of instability is suppressed. The electrochemical performance is improved, and the high-capacity advantage is exerted with a slight increase in cycling stability.