ZrO2包覆对层状氧化物正极材料储钠性能的改善

层状氧化物正极材料具有良好的结构稳定性和较高的充放电比容量，是一类理想的钠离子电池正极材料。本工作研究了层状氧化物正极材料NaNi1/3Fe1/3Mn1/3O2表面修饰对其电化学性能的影响，采用固相球磨法在正极材料表面包覆一层纳米ZrO2，采用形貌、结构、电化学方法等研究了包覆后性能改进机理。研究结果表明，ZrO2在NaNi1/3Fe1/3Mn1/3O2表面形成一层惰性保护层，有效隔开了电解液与正极材料的接触，缓解了电解液的分解速度，抑制了金属离子的溶出速度，从而显著改善了电池的循环性能以及高温性能。在ZrO2包覆修饰后，55℃下正极材料相比于未包覆的正极材料有明显提升，100次循环后容量保持率达到83.6%，高于未包覆的75.2%。此外，包覆后的NaNi1/3Fe1/3Mn1/3O2正极材料在空气环境存储后，稳定性得到明显提高。

Improved sodium storage performance of layered oxide cathode materials via ZrO2 coating

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 NaxMO2 (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 NaNi1/3Fe1/3Mn1/3O2 has been established as a promising cathode materials for practical sodium ion batteries. Many works have also focused their efforts on NaNi1/3Fe1/3Mn1/3O2 over the years and studied its synthesis method, large scale synthesis, electrochemical reaction mechanism, coating, doping and thermal stability. In this work, ZrO2 coating NaNi1/3Fe1/3Mn1/3O2 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 NaNi1/3Fe1/3Mn1/3O2, 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 NaNi1/3Fe1/3Mn1/3O2 cathode material was significantly improved after storage in air environment.