Analyzing the Doping Mechanism of High-Valence Element in Ni-Rich Cathode Materials

Layered cathode materials, LiMO 2 (M=Ni, Co,Mn, or Al), with a high nickel content are promising cathode materials owing to their near-theoretical specific capacity. However, the inherent chemical and structural instabilities of Ni-rich cathodes lead to several problems, including rapid capacity fading, thermal instability, gas evolution, and safety concerns. 1 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. 2 However, high-valence elements are likely to be insoluble in the crystal structure, resulting in accumulation along the interparticle boundaries. 3 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 LiNiO 2 (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. 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. References: [1] N.-Y. Park, G.-T. Park, S.-B. Kim, W. Jung, B.-C. Park, Y.-K. Sun, ACS Energy Lett. 2022 ,7, 2362. [2] X. Ou, T. Liu, W. Zhong, X. Fan, X. Guo, X. Huang, L. Cao, J. Hu, B. Zhang, Y. S. Chu, G. Hu, Z. Lin, M. Dahbi, J. Alami, K. Amine, C. Yang, J. Lu, Nat. Commun. 2022 ,13, 2319. [3] G.-T. Park, D. R. Yoon, U.-H. Kim, B. Namkoong, J. Lee, M. M. Wang, A. C. Lee, X. W. Gu, W. C. Chueh, C. S. Yoon, Y.-K. Sun, Energy Environ.Sci. 2021 ,14, 6616.