Explore the effect of Co Doping on P2-Na0.67MnO2 prepared by hydrothermal method as cathode materials for sodium ion batteries

Sodium-ion battery is considered to be one of the most promising candidates for energy storage systems. However, the energy density, rate performance, and cycle stability of sodium-ion batteries are still limited by cathode materials. To improve its electrochemical performance, we adopted doping Co at the Mn site to increase the proportion of Mn4+, suppressing the P2-P2 ' distortion generated by Mn3+. Here, layered oxides P2-Na0.67Mn1-xCoxO2 (x = 0, 0.1, 0.2) prepared by hydrothermal method. The prepared cathode materials have the characteristics of uniform dispersion and obvious layered structure. The XRD refinement results show that the lattice parameters a of Co-doped material is reduced, but the layer spacing d is enlarged, which can be conducive to the diffusion of Na+ and the improvement of rate performance along with firstprinciples calculations has been used to characterize the charge storage mechanism. Moreover, electrochemical performance tests show that NCM2 has superior electrochemical performance. At the ampere density of 2 C, the material still has 88.7% capacity retention rate combined with excellent cycle stability after 200 cycles.