Effect of niobium doping on the structure and electrochemical performance of LiNi0.5Co0.2Mn0.3O2 cathode materials for lithium ion batteries
Key issues including poor rate capability and limited cycle life span should be addressed for the extended application of LiNi0.5Co0.2Mn0.3O2 cathode. The suppressed Li+/Ni2+ site exchange, enlarged LiO2 inter-slab space and reduced impedance, which could facilitate the structure stability, were achieved by controlled Niobium (Nb) doping and contributed to enhanced performance even at elevated temperature (55 °C). The detailed role of the doped Nb was investigated thoroughly and systematically with the help of XRD, SEM, XPS and related electrochemical tests. The full and accurate results demonstrate that the Li(Ni0.5Co0.2Mn0.3)0.99Nb0.01O2 sample with appropriate Nb doping amount possess high capacity retention of 93.77% after 100 cycles at 1.0 C and improved rate performance with 125.5 mA h g−1 at 5.0 C, which are much better than that of the LiNi0.5Co0.2Mn0.3O2. Moreover, at high temperature of 55 °C, Nb doping shows more remarkable effect on stabilizing the structure and 88.63% of the initial reversible capacity could be retained, which is ~20% higher than the LiNi0.5Co0.2Mn0.3O2. This study intensively determines that controlled Nb doping could be effectively maintain the structure stability of advanced LiNi0.5Co0.2Mn0.3O2 cathode and promote the development of high energy density lithium ion batteries.