Layered lithium mixed-transition-metal oxides (NCM: LiNi1-x-yCoxMnyO2) with high nickel content (i.e., Ni-rich NCM) offer high electrochemical storage capacity, high operating potential, low toxicity, and relatively low cost. These compounds, however, exhibit poor structural and electrochemical stability. Zirconium, which has been studied as a substitutional element for transition metal in the layered NCM cathode materials, can stabilize the layered structure and improve the cyclability. However, the fundamental mechanism of the Zr-dopant is still unclear, especially in Ni-rich NCMs.
In this research, we synthesized Zr-doped LiNi0.8Co0.1Mn0.1O2 (Zr-NCM811) with a variety of dopant concentrations and systematically examined their structure, composition, phase, morphology, chemical state and electrochemical performance using XRD, ICP, SEM, TEM, and XPS. The 1 at.% Zr-NCM811 [Li(Ni0.8Co0.1Mn0.1)0.99Zr0.01O2] achieved the most stable cycling performance and the best high-rate capability with 165.2 mAh×g-1 at 2C (400 mA×g-1) cycling and 83.1% of retention after 60 cycles in contrast to 163.8 mAh×g-1 and 71.4% for the un-doped NCM811. The excellent high-rate performance of Zr-NCM811 can be attributed to the enhanced lithiation/delithiation kinetics, evidenced by conductivity and diffusivity measurements on the Zr-NCM811 materials.