Semiconductor Material ZnO-Coated P2-Type Na2/3Ni1/3Mn2/3O2 Cathode Materials for Sodium-Ion Batteries with Superior Electrochemical Performance

The P2-type layered oxide Na-2/3[Ni1/3Mn2/3]-O-2 cathode material is considered a promising material for sodium-ion batteries because of its high capacity and operating voltage together with a simple synthesis process. However, unfavorable electrochemical performance degradation during cycling is an obstacle to its practical application. Because ZnO has excellent electrical conductivity as a semiconductor material, it was selected for the coating modification study in this experiment. Transmission electron microscopy and energy-dispersive spectroscopy showed a uniform ZnO-coating layer on the surface of the particles with a thickness of 5 nm. When comparing the scanning electron microscope and X-ray diffraction (XRD) results of the electrodes before and after the cycle, we found that ZnO can inhibit the exfoliation phenomenon, and the morphology as well as the structure stability of the electrode were excellently maintained. In addition, according to the XRD refinement, part of Zn2+ entered the transition-metal oxides (TMO2) layer, which improves the stability of the crystal structure. On the basis of the synergistic effect between the ZnO coating and Zn2+ doping, the battery exhibited excellent cycle and rate performance. After 200 cycles at 0.5C (1C = 273 mA g(-1)), the battery still maintained a capacity of 70 mA h g(-1) and a capacity retention rate of 75%. Therefore, we believe that ZnO coating can effectively improve the electrochemical performances of batteries.