Multifunctional Doping Strategy to Develop High-Performance Ni-Rich Cathode Material

Abstract

A high fraction of reactive Ni4+ ions at the cathode–electrolyte interfaces lead to capacity fading of Ni-rich cathodes. Therefore, a core–shell (CS) design encapsulating the Ni-rich region by a Ni-less shell is an effective approach for improving the cycling stability of the cathodes. However, with increasing average Ni content to increase the capacity, the thickness of the shell should be reduced or the Ni fraction of the shell will be inevitably higher, making it susceptible to interdiffusion, which flattens the concentration gradient during the lithiation process. Herein, the limit of the average Ni composition in the CS-type cathode is pushed to 94% via Ta doping, which suppresses interdiffusion by segregating the Ta-rich phases at the particle boundaries. Ta doping allows the maintenance of the highly aligned microstructure and the ordered intermixing structure of Li and transition metal ions, as well as the concentration gradient, over a wide lithiation temperature range. The Ta-doped CS-type cathode retains 92.6% of its initial capacity after 1000 cycles and exhibits resistance to damage from fast charging. Multifunctional Ta doping in the CS-type cathode provides a simple and all-around solution to maximize the electrochemical performance of Ni-rich cathodes, providing flexibility in the lithiation process.