Dual‐Functional Surface Engineering of Single‐Crystal NMC Cathodes via Residue‐to‐Coating Conversion for Enhanced Interface Stability

Nickel‐rich layered oxides, such as LiNi _0.83 Mn _0.06 Co _0.11 O ₂ (NMC), are among the most promising cathode materials for high‐energy‐density lithium‐ion batteries. However, their practical implementation is limited by surface instability and the presence of residual lithium compounds, which degrade performance and complicate scalability. In this study, a dual‐functional surface modification strategy using lithium dihydrogen phosphate (LiH ₂ PO ₄ ) is presented. A wet impregnation procedure is used to transform the residual surface contaminants (LiOH, Li ₂ CO ₃ ) into an advantageous surface coating (Li ₃ PO ₄ ) on single crystal nickel‐rich (SCNMC) cathode materials rather than directly eliminating them through solvent washing process., as confirmed by titration and in situ Gas Chromotography‐Mas (GC‐MS), while the resulting ≈4 nm Li ₃ PO ₄ layer enhances structural stability, suppresses nickel migration, and mitigates electrolyte‐induced side reactions. Electrochemical tests reveal significantly improved cycling stability (72.96% capacity retention after 100 cycles at 0.2C compared to 18.25% for pristine SCNMC) and enhanced rate capability, supported by improved Li ⁺ diffusion kinetics. Synchrotron X‐ray Absorption Spectroscopy (XAS) and post‐mortem analyses further confirm the preservation of Ni oxidation states and reduced cross‐talk effects.