Bulk Al-doping effect on structure and electrochemical performance of NCM811 cathode materials

Bulk doping of aluminum ions (Al3+) is promising to solve the problems of poor safety and short cycling life of nickel-rich cathodes. A crucial chelating agent of sodium lactate is found here to realize the best co-precipitation of Al3+ with other transition-metal ions at an atomic level for the first time. The discharge capacity of this cathode is increased by 13.17% at 1 C, while its cycle retention is promoted by 12.76% compared to a commercial counterpart. Additionally, the amount of chelating agent complexed with Al3+ is optimized, and the gradient directions of Al-doping for the full concentration gradient materials are also investigated. It is found that the gradually increased Al3+ concentration from core to shell can integrate the surface coating and bulk doping, improving the electrochemical performance. Its discharge capacity is 149.3 mAh/g at a high rate of 5 C. An approach for bulk Al-doping and synthesis of commercial NCA cathode materials is provided.