Preparation And Modification Of Cathode Material Na₂Ni₂TeO₆ For Sodium Ion Batteries

Lithium-ion batteries（LIBs）have been widely used in portable electronic devices,owing to their excellent performances.However,limited lithium resource cannot meet the rapid increasing market demand.Thus,rechargeable batteries based on alternative,abundantly available materials need to be developed.Sodium-ion batteries（NIBs）are a promising alternative to LIBs for large-scale energy storage applications,due to high availability of sodium,low cost,and the similarity in the intercalation chemistry of sodium and lithium.Na₂Ni₂TeO₆ and Al₂O₃ modified Na₂Ni₂TeO₆ were prepared by a high temperature solid-state method in the work.Various test methods are applied to characterize the physicochemical properties and electrochemical behaviors of the samples.The main research works are as follow:（1）Na₂Ni₂TeO₆ was prepared using high temperature solid-state method.The cathode material was characterized by X-ray diffraction（XRD）,scanning electron microscope（SEM）and charge-discharge test.The results show that the material sintered at 650℃for 12 h,followed by 900℃for 24 h with stoichiometric sodium content exhibit good crystal structure and excellent electrochemical performance.The cathode delivers a first discharge capacity of 60.1 mAh g^-1 at 0.1C in the range of 3.0⁴.5 V,and the coulombic efficiency is 57.6%.However,the discharge capacity is only 24 mAh g^-1after 30 cycles.These results indicate the sample Na₂Ni₂TeO₆ exhibits a higher initial charge-discharge capacity,but its cycling performances need to be further improved.（2）The properties and electrochemical performances of Al₂O₃ modified Na₂Ni₂TeO₆ were investigated.The structure and electrochemical performances were studied by XRD,SEM,EDX and charge-discharge tests.The results show that Al₂O₃existed only on the surface,and had no effect on the crystal structure.4wt%Al2O3modified Na₂Ni₂TeO₆ exhibits highest discharge capacity and best cycle performance.Its capacity is 40 mAh g^-1 at 0.1C,after 30th cycle,while the capacity of the pristine material is only 24 mAh g^-1.At the same time,the initial charge-discharge capacity of the pristine material is 104.4 mAh g^-1 and 60.1 mAh g^-1 at 0.1C and the first coulombic efficiency is 57.57%.After 4 wt%Al2O3 modification,the charge-discharge capacity is112.2 mAh g^-1 and 76.1 mAh g^-1,and the efficiency is enhanced to 67.8%,The improved-electrochemical performances show the modification amount for the cathode material is crucial to the performance improvement.