Improving the Cycle Stability of LiNiO₂ through Al³⁺ Doping and LiAlO₂ Coating

In this study, we addressed the poor cycling and rate performance of LiNiO₂, a material with ultrahigh nickel content considered a strong contender for high-energy-density lithium-ion battery cathodes. We introduced nano-Al₂O₃ during the lithiation process to achieve dual modified material through bulk phase element doping and in situ LiAlO₂ coating. Comparison revealed notable improvements in the modified materials. In particular, LiNi_0.99Al_0.01O₂ maintained a capacity retention rate of 73.1% after 300 cycles in a long-cycle test at 0.5C current density, outperforming the undoped material. In rate performance tests, the doped samples consistently exhibited higher discharge-specific capacities than that of the undoped counterpart. Notably, at a high current density of 5C, LiNi_0.99Al_0.01O₂ exhibited a discharge-specific capacity of 101.75 mAh g^-1. The results indicate that an appropriate amount of Al doping can effectively stabilize the layered structure of the cathode material and delay the irreversible phase transition from H2 to H3. Further, Al doping facilitates the formation of a LiAlO₂ coating on the surface of the particles. This coating acts as a fast-ion conductor, enhancing the transport of lithium ions and reducing the erosion of the active material by the electrolyte.