Enhancing the Cycling Stability of Ni-Rich LiNi0.6Co0.2Mn0.2O2 Cathode at a High Cutoff Voltage with Ta Doping

Ni-rich cathode materials have attracted wide attention on account of their high specific capacity. However, the poor cycle retention of Ni-rich cathode materials, especially at high voltage or high temperature, is recognized as the main obstacle for extensive commercialization. In this research, we propose a new strategy of doping NCM622 (LiNi0.6Co0.2Mn0.2O2) with Ta5+ to improve the structural stability due to the high Ta-O dissociation bond energy. XRD refinement results indicate that almost all Ta5+ are located in Li sites to play a pillar role and cation mixing is inhibited. Electrochemical impedance spectroscopy results show that the increase of charge transfer impedance during the cycling process is controlled. Owing to the stable structure, NCM622 with 0.25% Ta doping exhibits a capacity of 148.1 mAh g(-1) with retention reaching 83.6% at 1 C over 3.0-4.5 V after 100 cycles, whereas the bare NCM622 only delivers 143.4 mAh g(-1) with a retention of 80.1%. The above results signify that moderate Ta doping is a facile yet effective strategy to develop high-performance Ni-rich cathode materials.