Selective TiO₂ Nanolayer Coating by Polydopamine Modification for Highly Stable Ni-Rich Layered Oxides

Ni-rich layered oxides are promising cathode materials for developing high-energy lithium-ion batteries. To overcome the major challenge of surface degradation, a TiO₂ surface coating based on polydopamine (PDA) modification was investigated in this study. The PDA precoating layer had abundant OH catechol groups, which attracted Ti(OEt)₄ molecules in ethanol solvent and contributed towards obtaining a uniform TiO₂ nanolayer after calcination. Owing to the uniform coating of the TiO₂ nanolayer, TiO₂-coated PDA-LiNi_0.6Co_0.2Mn_0.2O₂ (TiO₂-PNCM) displayed an excellent electrochemical stability during cycling under high voltage (3.0–4.5 V vs. Li⁺/Li), during which the cathode material undergoes a highly oxidative charge process. In addition, TiO₂-PNCM exhibited excellent cyclability at elevated temperature (60 °C) compared with the bare NCM. The surface degradation of the Ni-rich cathode material, which is accelerated under harsh cycling conditions, was effectively suppressed after the formation of an ultra-thin TiO₂ coating layer.