Comprehensive Study of Ti and Ta Co-Doping in Ni-Rich Cathode Material LiNi0.8Mn0.1Co0.1O2 Towards Improving the Electrochemical Performance.

Abstract

Layered Ni-rich oxides (LiNi1-x-yCoxMnyO2) 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 LiNi0.8Mn0.1Co0.1-x-yTixTayO2 (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 Ti4+ and Ta5+ co-doped cathode LiNi0.8Mn0.1Co0.09Ti0.005Ta0.005O2 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 3rd and 50th cycles are 9.9×10-10 cm2 s-1 and 9.3×10-10 cm2 s-1 respectively, which is higher than that of the pristine cathode (3.3×10-10 cm2 s-1 and 2.5×10-10 cm2 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.