Effect of Nb doping on the behavior of NCA cathode: Enhanced electrochemical performances from improved lattice stability towards 4.5V application

Abstract

Although the Ni-rich LiNi0.8Co0.15Al0.05O2 (N85CA) material has been used as the commercial cathode of electric vehicle battery, the instability of the layered structure and the short lifespan under high voltage cycling prevent its practical application to higher energy density. Herein, Nb-doped N85CA material, with enhanced structural stability and improved cycle stability, is reported to work at 4.5V. In particular, Nb0.5%-N85CA shows the best electrochemical performance, with a discharge capacity of 200.2 mAh/g at 0.1C, and a retention of 94.19% after 100 runs at 0.5 C. As a comparison, the data of the pristine N85CA are 210.2 mAh/g and 69.46%, respectively. Such an obvious increase in the capacity retention is caused by the promoted lattice stability provided by the strong Nb–O bond that inhibits the H2–H3 phase transition in the electrochemical process. The incorporation of Nb5+ ions further increases the interslab thickness that enable a rapid migration of Li ions (2.23 × 10−10 S cm−1 vs. 8.32 × 10−11 S cm−1), and the rate behavior of the cathode is also enhanced. Furthermore, Nb0.5%-N85CA material displays a specific capacity of 156.2 mAh/g at 5 C, while that of the pristine N85CA is 123 mAh/g. The results strongly indicate that such Nb-doped N85CA material has high potential as a cathode candidate, especially for high energy applications.