Non-Corrosive Methide-Based Lithium Salt for Stabilizing Ni-Rich NMC Cathodes

High-nickel LiNi_xMn_yCo_1-x-yO₂ (NMC) cathodes are promising for next-generation lithium-ion batteries (LIBs) due to their high energy density, but their performance is limited by interfacial instability with conventional electrolytes. While lithium hexafluorophosphate (LiPF₆) is widely used, its chemical instability (e.g., generating HF) undermines battery performance. Lithium imides such as lithium bis(trifluoromethanesulfonyl)imide (LiNTf₂) improve chemical stability but corrode aluminum current collectors above 3.7 V, motivating the development of non-corrosive alternatives. Herein, we report a non-corrosive methide-based lithium salt, lithium bis(trifluoromethanesulfonyl)methide (LiCTf₂), in which the central nitrogen of LiNTf₂ is replaced by a methine (─CH─) moiety, modulating the electronic structure of the CTf₂ ^- anion to promote the formation of low-solubility Al³⁺ complexes and thus suppress corrosion, while enhancing coordination with Li⁺ to reinforce solvation structures and establish denser interphase. This design realizes interfacial stabilization, as evidenced by electrochemical and microscopic characterization. Consequently, LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532) and LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cycled in LiCTf₂-based electrolyte exhibit enhanced cycling stability compared with LiNTf₂ and LiPF₆. Notably, the excellent performance of LiCTf₂ is achieved without any film-forming additives, highlighting its intrinsic interfacial engineering capability. These results provide valuable insights into optimizing electrolyte formulation, offering a promising approach to enhancing the electrochemical stability and cycling performance of NMC cathodes and beyond.