ZrO₂包覆对层状氧化物正极材料储钠性能的改善

Lithium ion batteries have been successfully applied in portable electronic products, the application of lithium ion batteries is expanding to the fields such as large scale energy storage grid and electric vehicles. However, the considerably increased demand of lithium ion batteries might yield problems in the future with the limit of Li resources. Compared with lithium, sodium is abundant in the earth. Based on its resource and cost advantages, sodium ion batteries hold promise for low-cost energy storage and could be key for smart electric-grid of the future. To date, a large variety of cathode materials with satisfactory performance have been proposed. These cathode materials include layered transition metal oxides, Prussian blue analogues, polyanionic-type compounds and organic-based materials. Layered transition metal oxides Na_xMO₂ (M=Mn, Fe, Ni, Co, Ti, V, Cr) have been extensively investigated because of their higher capacities and industrial feasibility. Up to now, layered transition metal oxide NaNi_1/3Fe_1/3Mn_1/3O₂ has been established as a promising cathode materials for practical sodium ion batteries. Many works have also focused their efforts on NaNi_1/3Fe_1/3Mn_1/3O₂ over the years and studied its synthesis method, large scale synthesis, electrochemical reaction mechanism, coating, doping and thermal stability. In this work, ZrO₂ coating NaNi_1/3Fe_1/3Mn_1/3O₂ cathode was prepared by a solid state method, and the coating effect was evaluated by electrochemical measurements as well as morphological, structural, and chemical composition analyses. The results showed that ZrO₂ formed an inert protective layer on the surface of NaNi_1/3Fe_1/3Mn_1/3O₂, which effectively separated the contact between electrolyte and cathode material, alleviated the decomposition rate of electrolyte and inhibited the dissolution rate of metal ions, so as to significantly improve the cycle performance and high temperature performance of the battery. After ZrO₂ coating modification, the cathode material was significantly improved compared with the uncoated cathode material at 55℃, and the capacity retention rate reached 83.6% after 100 cycles, which was higher than 75.2% of the uncoated cathode material. In addition, the stability of the coated NaNi_1/3Fe_1/3Mn_1/3O₂ cathode material was significantly improved after storage in air environment.