Dual modification of phosphate toward improving electrochemical performance of LiNiO₂ cathode materials

Lithium nickel oxide (LiNiO₂) cathode materials are featured with high capacity and low cost for rechargeable lithium-ion batteries but suffer from severe structure and interface instability. Bulk doping together with surface coating has been proven to be an efficient approach to improve the inner structure and interfacial stability of the LiNiO₂ cathode material. Nevertheless, the role of anion doping seems to be quite different from that of cation doping, and a deep insight will be desirable for the structure design of the LiNiO₂ cathode material. In this paper, PO₄^3--doped and Li₃PO₄-coating of dual modification of LiNiO₂ are achieved via a facile approach. It is demonstrated that the PO₄^3- anions are doped into the tetrahedron vacant sites of the crystal structure, alleviating the phase transition and improving the reversibility of crystal structure. Besides, the Li₃PO₄ coating layer ameliorates the interface stability to restrain the side reactions. Therefore, the dual modification enhances overall structural stability of the material to provide excellent performance. Moreover, the consumption of the Li residues by the formation of Li₃PO₄ coating layer, and the enlarged interlayer spacing of the crystal structure by PO₄^3- doping can facilitate the Li⁺ ions diffusion, resulting in a superior rate capability.