Dual modification of LiNi_0.83Co_0.11Mn_0.06O₂ cathode materials by K⁺ doping and Li₃PO₄ coating for lithium ions batteries

Li₃PO₄@Li_0.99K_0.01Ni_0.83Co_0.11Mn_0.06O₂ (NCM-KP) cathode powders are synthesized via K⁺ doping in calcination processes and H₃PO₄ coating in sol–gel processes. K⁺ precisely enters into the lattice to widen the (003) plane to 0.4746 nm with a lower cationic disordered degree of 1.87%. Moreover, the surface residual lithium salts are treated by H₃PO₄ to generate a uniform Li₃PO₄ coating layer of approximately 11.41 nm, which completely covers on the surface of secondary spherical particles to improve the interfacial stability. At 25 °C, the NCM-KP electrode delivers a discharge specific capacity of 148.9 mAh·g⁻¹ with a remarkable capacity retention ratio of 84.1% after 200 cycles at 1.0C and retains a high reversible specific capacity of 154.4 mAh·g⁻¹ at 5.0C. Even at 1.0C and 60 °C, it can maintain a reversible discharge specific capacity of 114.6 mAh·g⁻¹ with 0.21% of capacity decay per cycle after 200 cycles, which is significantly lower than 0.40% for the pristine NCM powders. Importantly, the charge transfer resistance of 238.89 Ω for the NCM-KP electrode is significantly lower than 947.41 Ω for the pristine NCM one by restricting the interfacial side reactions. Therefore, combining K⁺ doping and Li₃PO₄ coating is an effective strategy to enable the significant improvement of the electrochemical property of high-nickel cathode materials, which may be mainly attributed to the widened diffusion pathway and the formed Li₃PO₄ protective layer, thus promoting Li⁺ diffusion rate and preventing the erosion of HF.