Synergistic Modification and Mechanism of Tungsten and Niobium to Enhance the Performance of Nickel-Rich Layered Cathode Materials.

To improve the capacity at a high rate and cycle stability of LiNiCoMnO (NCM811), a simple strategy is developed to synthesize the tungsten/niobium (W/Nb) co-doped cathode material. W/Nb co-doping remarkably reduced the system energy of single W- or single Nb-doping. The co-doping makes the material have a more stable structure, and inhibits the anisotropic volume change caused by H2↔H3 phase transition, thus maintaining the integrity of particles and preventing the formation of microcracks. Moreover, the passivation layer formed by co-doping prevents the occurrence of side reactions as well as the formation of microcracks. The synergistic effect of W and Nb is also conducive to inhibiting the formation of internal oxygen vacancies and surface LiCO. For the W/Nb co-doped sample, the capacity retention of 54.9% after 400 cycles and 52.3% after 500 cycles are maintained even at high currents of 5.0 and 10.0 C, respectively. The strategy of synergistic effect on enhancing co-doping with high valence cations can be spread as a simple and practical method to improve the electrochemical performance of nickel-rich layered cathode materials for lithium-ion batteries at high cut-off voltage.