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 first-principles 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.