A Synergistic Modification of Surface Coating and TM/Li Layer Doping by Li_1.2Zr_1.9Mg_0.1(PO₄)₃ to Improve the Structural and Cycling Stability of LiNi_0.90Co_0.05Mn<sub>0.05</s

Enhancing the surface and structural stability has been a research focus of nickel-rich layered cathode materials in lithium-ion batteries (LIBs). This work introduced a dual-functional modification strategy. LZMP is coated on the LiNi0.90Co0.05Mn0.05O2 (NCM90) particle surface to protect the cathode particles from erosion by air and acidic electrolyte, suppressing side reactions between the cathode and H2O, CO2, and HF, and hence enhances the stability of the cathode–electrolyte interphase film. Meanwhile, NCM90 is doped with Zr4+ and Mg2+, which substitute for Ni3+ in the lattice transition metal layer and Li+ in the lithium layer, respectively. Zr4+ forms a stronger Zr–O bond, while Mg2+ performs as a pillar ion, suppressing variations of the lattice parameters and maintaining the layered structure during cycling. The enhanced surface and bulk structural stabilities improve the cycling and rate performances of the cathode material. At 25 °C, 1C, and 2.7–4.3 V, the initial discharge specific capacity and the capacity retention after 200 cycles of 1%LZMP–NCM90 were 180.9 mAh g–1 and 86.0%, respectively, exceeding those of NCM90 (172.7 mAh g–1 and 76.4%). In summary, the LZMP modification synergistically alleviates the surface and bulk structure deterioration, thus preserving the electrochemical performance and improving the structural and cycling stability of NCM90.