Study On Preparation And Modification Of Na_0.67MnO₂ Cathode Material For Sodium-ion Batteries

As the most promising cathode materials for sodium-ion batteries,layered manganese oxide exhibits high theoretical specific capacity,low cost and environmental friendliness.However,it undergoes different degrees of phase transitions during the charging and discharging process,resulting in poor electrochemical performance.In addition,due to the hydration reaction,the surface structure degrades when it is stored in humid air.Therefore,storage conditions are extremely harsh.To address these problems,this study investigates the process of preparing pure phase materials.Elemental doping and surface functionalization are used to suppress the phase transition and improve the storage stability.The pure phase Na_0.67MnO₂ cathode material was prepared by sol-gel method.The influence of solution ambient p H on the electrochemical performance of the material was investigated in detail.With the increase of p H,the material transformed from irregular block stacking to regular hexagonal flake stacking,which effectively exposed the dominant crystal surface of sodium ion deintercalation.It has the best electrochemical performance at p H6.It has a discharge specific capacity of 93.8 m Ah g^-1 at5 C and a capacity retention rate of 79.95%after 100 cycles at 1 C.The Na_0.67Mn_1-x-yCu_xFe_yO₂ modified samples were prepared by the sol-gel method.The optimum elemental doping amounts were x=0.04 as well as y=0.04.The elemental doping effectively disrupts the ordered arrangement of Na⁺/vacancies in the material,smooths the charge/discharge curve,and suppresses the transition of the crystal structure from P2 to OP4 phase in the highly desodium state,which effectively improves the structural and cyclic stability.Thanks to the synergistic effect of copper and iron,the Na_0.67Mn_1-x-yCu_xFe_yO₂ sample exhibits a capacity retention rate of 94.35%after 100 cycles at 1 C.In addition,it has a discharge specific capacity of 91.8 m Ah g^-1 at 10 C.On this basis,surface functionalization was used to improve the poor storage stability.After 28 days of storage in humid air,the surface-functionalized sample effectively inhibited the hydration reaction and has a capacity retention of 92.22%after 100 cycles at 1 C.It also maintains a good crystal structure and surface morphology.