Dual-Functional Surface Engineering of Single-Crystal NMC Cathodes via Residue-to-Coating Conversion for Enhanced...

Nickel-rich layered oxides, such as LiNi_0.83Mn_0.06Co_0.11O₂ (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 (LiH₂PO₄) is presented. A wet impregnation procedure is used to transform the residual surface contaminants (LiOH, Li₂CO₃) into an advantageous surface coating (Li₃PO₄) 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 Li₃PO₄ 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.