Research progress on the stability of layered cathode materials for sodium-ion batteries

The layered cathode materials of NaxMeO2 (Me=Ni, Co, Fe, Mn and other elements) for sodium-ion batteries hold the advantages of high energy density, high redox potential, and abundant resources. However, the layered cathode materials were unstable in air and during the charge-discharge process, which seriously affects the composition and structure of the materials, and deteriorates the electrochemical performance of the battery, leading to the restrictive commercial application of sodium-ion batteries. In recent years, based on the stability of layered cathode materials, the chemical reaction process in the air have reported, and the destabilization mechanism were analyzed. Different strategies have been adopted to improve the stabilization characteristics, then promote the applications of layered cathode material in sodium-ion batteries. This word summarized the research progress on the stability of layered cathode materials for sodium-ion batteries. The reaction process of NaxMeO2 with H2O and CO2 in the air to generate NaOH, Na2CO3, NaHCO3 were reviewed, and the phase transformation of NaxMeO2 cathode materials during the charging and discharging process were discussed. The research progress of element doping, theoretical calculation and detection methods in the investigation of stability characteristics for layered cathode materials are analyzed. Finally, the application of layered cathode materials in Na-ion batteries was prospected.