Improving the electrochemical performances and structural stability of ultrahigh-Ni cathodes by using multi-element co-doping methods

Multi-element co-doping and its impact on the stability of the ultrahigh-Ni cathodes during extended cell cycling have not yet been fully established. Synergistic mechanisms still need to be thoroughly understood, and there is potential for further enhancing the structural stability and electrochemical performance of layered cathode materials. In this work, an Nb and Mg co-doped ultrahigh-Ni cathodes (LiNi0.92Co0.06Mn0.02O2) is prepared by solid-state synthesis methods. The effect of Nb and Mg dopants on the microstructure and electrochemical properties are systematically investigated. It is found that the Nb dopant can overcome the main shortcomings provided by Mg doping, including increasing the unit cell volume, suppress harmful phase transformation and enhancing lithium-ion diffusion kinetics. The cathode materials with optimized amounts of Nb and Mg dopants are demonstrated with excellent electrochemical performances. They reveal a specific capacity of 191 mAh g-1 at 1 C with a good capacity retention of 92.8% after 500 cycles and a rated capacity of 141 mAh g-1 at 10 C. It is also found that excessive Nb doping could lead to a decrease in rhombohedral ordering for crystal lattices, resulting in reduced structural stability and cyclability. This work investigates the strategy of Nb and Mg co-doping for enhancing electrochemical performances of ultrahigh-Ni cathodes, and the results obtained from this work can provide insights into improve the cyclability of these materials.