Bulk Mg-doping and surface polypyrrole-coating enable high-rate and long-life for Ni-rich layered cathodes

The severe capacity deterioration of Ni-rich oxides (content of Ni ≥ 90%) limits the practical application for high-energy and long-life Li-ion batteries due to structure pulverization and surface parasitic reactions. Herein, a dual-modification tactic of bulk Mg-doping and surface poly-pyrrole (PPy)-coating is applied to enhance layered Ni-rich cathode materials. The as-formed pinning ions of Mg effectively inhibit the anisotropic lattice changes and the Li/Ni disorder, therefore stabilizing the crystal and phase structures. The thin and uniform PPy coating layer physically prevents the detrimental parasitic reactions, and meantime accelerates the charge transfer rate at cathode-electrolyte interface. These two advantages endow the modified Ni-rich oxides with a superior reversible capacity of 213.0 mAh g−1 at 0.2 C and 144.7 mAh g−1 at 10 C. Impressively, the capacity retention can reach 99.2% after 100 cycles at 0.2 C without voltage drop and structure damage. This dual-modification strategy may be further extended to other cathode materials to improve their high-rate and cycling performances.