Ta/Ti Codoped Concentration Gradient High-Ni Cathodes for Long-Life Li-Ion Batteries

Abstract

Full concentration gradient nickel-rich ternary materials (GNCM) demonstrate cost-effectiveness and higher discharge capacity as lithium-ion battery (LIB) cathodes. However, unsatisfactory rate performances of GNCM are recognized as a limitation caused by concentration gradient elimination and surface Mn enrichment during the calcination process. To address this issue, a Ta/Ti codoping approach is developed, showing that Ta⁵⁺ can upgrade the surface of the primary particle to mitigate element diffusion at the grain boundaries, and meanwhile, Ti⁴⁺ can stabilize Ni–O to weaken Ni²⁺ migration. Such impacts on GNCM bring in significant advantages in terms of structure and performance to prevent irreversible phase transitions from the layered to the rock-salt structure and accelerate the diffusion kinetics of Li⁺ and electrons with increased electric conductivity. Consequently, the Ta/Ti codoped GNCM (labeled as GNCM-TaTi) delivered a high reversible capacity of 210.9 mAh/g at an initial rate of 0.1C and maintained 106.8 mAh/g even at a high rate of 10C. The capacity retentions can remain 98.2 and 94.7% after 100 cycles at 0.5 and 3C, respectively. Further evaluations of GNCM-TaTi in a pouch cell show a capacity retention of 90.3% at 3C after 500 cycles. The presented Ta/Ti codoping validates an effective route to strengthen the LIB performance of the high-Ni NCM with a full concentration gradient structure.