Comprehensive Study of Ti and Ta Co-Doping in Ni-Rich Cathode Material LiNi 0.8 Mn 0.1 Co 0.1 O 2 Towards Improving the Electrochemical Performance.

Layered Ni-rich oxides (LiNi 1-x-y Co x Mn y O 2 ) 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 LiNi 0.8 Mn 0.1 Co 0.1-x-y Ti x Ta y O 2 (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 4+ and Ta 5+ co-doped cathode LiNi 0.8 Mn 0.1 Co 0.09 Ti 0.005 Ta 0.005 O 2 exhibits a superior initial discharge capacity of 161.1 mAh g -1 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 rd and 50 th cycles are 9.9×10 -10  cm 2  s -1 and 9.3×10 -10  cm 2  s -1 respectively, which is higher than that of the pristine cathode (3.3×10 -10  cm 2  s -1 and 2.5×10 -10  cm 2  s -1 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.