Oriented Gradient Doping of Zirconium in Ni-Rich Cathode to Achieve Ultrahigh Stability and Rate Capability.

Ni-rich layered oxide materials exhibit great prospects for practical applications in lithium-ion batteries due to their high specific capacity. However, the poor cycling performance and suboptimal rate performance have caused obstacles for their widespread application. Herein, we developed a gradient Zr element doping method based on the bulk gradient concentration of Ni-rich layered oxide material to reinforce the cycle stability and rate performance of the cathode. In particular, the orientations of the gradient Zr doping were achieved via coprecipitation in a positive or negative correlation between the concentrations of Zr and Ni, and it was revealed that the material behaves better when the Zr content is abundant in the core. The gradient doping of Zr decreases the content of Ni and mitigates the mixing degree of Li and Ni, implying the superior performance of doped cathode material. Compared with the bare sample (70.7%, 121.4 mAh g), the Zr-doped sample delivered a higher capacity retention of 85.6% after 300 cycles at 1C (1C = 180 mA g) and exhibited a considerable rate performance of 122.5 mAh g at 20C. In particular, the Zr-doped cathodes performed dramatically on high rate cycling at 10C, with an initial capacity of 143.6 and 103.9 mAh g after 300 cycles. Furthermore, the Zr-doped cathode delivered significant stability at a high potential of 4.5 V with a capacity retention of 72.1% after 300 cycles, while that of the bare sample was only 37.4%. The concept of gradient doping strategies during coprecipitation offers new insight into the design of advanced cathodes with excellent cycling stability and rate capability.