Mechanism of Doping with High-Valence Elements for Developing Ni-Rich Cathode Materials

Abstract

Introducing additional elements into Ni-rich cathodes is an essential strategy for addressing the instability of the cathode material. Conventionally, this doping strategy considers only the incorporation of additional elements into the bulk structure of the cathode in terms of fortifying the crystal structure. However, high-valence elements such as Nb5+, Ta5+, and Mo6+ are likely to be insoluble in the crystal structure, resulting in accumulation along the interparticle boundaries. Herein, a new mechanism for doping high-valence elements into Ni-rich cathodes and their effects on the morphology and crystal structure are investigated by calcining LiNiO2 (LNO) and X-doped LNO cathodes (X = Al, Nb, Ta, and Mo) at various temperatures. Operando X-ray diffraction analysis reveals that the temperature at which the content of Li-X-O compounds declines is higher for the dopants with high oxidation states, reinforcing segregation at the grain boundary and widening the calcination temperature range. Thus, the highly aligned microstructure and high crystallinity of the LNO cathode are maintained over a wide calcination temperature range after doping with high-valence elements, enhancing the electrochemical performance. As next-generation dopants, high-valence elements can fortify not only the crystal structure, but also the microstructure, to maximize the electrochemical performance of Ni-rich cathodes.