Polydopamine-assisted coating layer of a fast Li-ion conductor Li_6.25La₃Zr₂Al_0.25O₁₂ on Ni-rich cathodes for Li-ion batteries

Ni-rich cathode materials have promising applications in lithium-ion batteries owing to their high energy density and reasonable cost. The surface stabilization of these materials is vital for achieving excellent electrochemical performance. In this study, a fast ionic conductor, Li_6.25La₃Zr₂Al_0.25O₁₂ (LLZAO), was successfully coated on the surface of LiNi_0.88Co_0.05Mn_0.07O₂ (LNCM) using a polydopamine (PDA) modification method. The abundant catechol groups of the intermediate PDA layer on the Ni_0.88Co_0.05Mn_0.07(OH)₂ (NCM(OH)₂) precursor attracted metal ions in an aqueous solution, and a uniform LLZAO coating layer was formed after calcination under an O₂ flow. The presence of the LLZAO protective film on the surface of LNCM was confirmed using several characterization techniques. The LLZAO-coated LNCM exhibited superior electrochemical properties compared to those of the pristine LNCM. Moreover, the LLZAO-coated LNCM demonstrated excellent electrochemical stability even at a high temperature (60 ℃). The deterioration of the surface structure of LNCM was significantly suppressed by the formation of the LLZAO coating layer, and LLZAO improved the Li⁺ ion transport at the electrode/electrolyte interface.