Abstract: The nanoparticles of Na_0.67Mn_0.67Ni_0.33O₂ and Co-Na_0.67Mn_0.67Ni_0.33O₂ are prepared by co-doping multi-metal Ni and Co with Na_0.91MnO₂ though the simple hydrothermal combined calcination method, and their electrochemical properties are optimized as cathode electrode materials for sodium ion batteries. The prepared particles with the size about 300 nm have been the uniform composition and uniform morphology. As the cathode for sodium ion batteries, the initial charge and discharge capacity of Na_0.67Mn_0.67Ni_0.33-xCo_xO₂ are above 160 mA·h·g^-1at 0.1C, and the capacity remained at 120 mA·h·g^-1 after 200 cycles. It shows that the Ni and Co ions are located in the transition metal sites could improve the specific capacity of nanoparticles (Ni) and increase the sodium ion diffusion of electrode materials (Co). The synergetic effects of Co and Ni substitution could effectively improve the specific capacity, rate and cycle performance of the cathode for sodium ion batteries.

Key words: sodim manganate, multi-metal substitution, sodium ion battery, cathode material, sodium ion diffusion