Comprehensive Study of Ti and Ta Co-Doping in Ni-Rich Cathode Material LiNiMnCoO Towards Improving the Electrochemical Performance.

Layered Ni-rich oxides (LiNiCoMnO) cathode materials are of current interest in high-energy-demanding applications, such as electric vehicles because of high discharge capacity and high intercalation potential. Here, the effect of co-doping a small amount of Ti and Ta on the crystal structure, morphology, and electrochemical properties of high Ni-rich cathode material LiNiMnCoTiTaO (0.0≤x+y≤0.2) was systematically investigated. This work demonstrates that an optimum level of Ti and Ta doping is beneficial towards enhancing electrochemical performance. The optimal Ti and Ta co-doped cathode LiNiMnCoTiTaO exhibits a superior initial discharge capacity of 161.1 mAh g at 1 C, and excellent capacity retention of 87.1 % after 250 cycles, compared to the pristine sample that exhibits only 59.8 % capacity retention. Moreover, the lithium-ion diffusion coefficients for the co-doped cathode after the 3 and 50 cycles are 9.9×10 cm s and 9.3×10 cm s respectively, which is higher than that of the pristine cathode (3.3×10 cm s and 2.5×10 cm s respectively). Based on these studies, we conclude that Ti and Ta co-doping enhances structural stability by mitigating irreversible phase transformation, improving Li-ion kinetics by expanding interlayer spacing, and nanosizing primary particles, thereby stabilizing high-nickel cathode materials and significantly enhancing cyclability.