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

High-nickel LiNixMnyCo1-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, LiNi0.5Mn0.3Co0.2O2 (NMC532) and LiNi0.8Mn0.1Co0.1O2 (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.