Effect of Niobium Doping on Structural Stability and Electrochemical Properties of LiNiO2 Cathode for Li-Ion Batteries

Abstract

LiNiO2, a promising cobalt-free cathode, suffers from poor cyclic stability and inferior rate performance due to structural degradation. A strategy based on the synergistic effect of a strong Nb–O bond (753 kJ mol−1), high valence state (Nb5+), and larger ionic radius (0.64 Å) was developed to improve the properties of LiNiO2. The synergistic effects can effectively improve lattice stability, lower Li+/Ni2+ cation mixing, expand LiO6-slab spaces, enhance the conductivity and inhibit the H2–H3 phase transition, which can enhance the stability of the layered structure, accelerate Li+ diffusion and alleviate mechanical damage. Therefore, LiN0.99Nb0.01O2 exhibits higher capacity retention (91.4% after 100 cycles at 0.5C) and superior rate capability (143 mAh g−1 at 5C). As a comparison, the data of bare LiNiO2 is 69.2% and 127 mAh g−1 under the same conditions. These results further demonstrate the effectiveness of the proposed doping strategy.