Preparation Of Na₃（VOPO₄）₂F Electrode Materials And The Application On Energy Storage Devices

In recent years,room temperature sodium ion storage devices have attracted widespread attention due to the abundant sodium resources,low cost and similar chemical/electrochemical properties to lithium.It is one of the important development directions for the next-generation low-cost,large-scale energy storage.Sodium vanadium fluorophosphate is a typical Na-superionic conductor（NASICON）structure cathode material with high operating voltage（>3.7V）and large theoretical capacity(128mAh g^-1),but low electronic conductivity limits its application in practice.In this thesis,the Na₃（VOPO₄）₂F@rGO composite material was successfully prepared by in-situ compounding with graphene oxide（GO）,which greatly improved the rate performance of the material,and then selected the appropriate anode material and electrolyte to assemble high energy density and power density sodium ion battery.The specific research contents include the following points:（1）Proposed the synthesis strategy of interfacial redox self-assembly,in-situ prepared Na₃（VOPO₄）₂F@rGO composite by hydrothermal method and determined the most optimized GO additions.The effects of the addition of GO on the final synthesized product were studied by X-ray photoelectron spectroscopy（XPS）,infrared spectroscopy and ultraviolet spectroscopy.It was proved that with the increase of GO addition,the product gradually changed from Na₃（VPO₄）₂F₃ to Na₃（VOPO₄）₂F while GO is reduced to rGO.Electrochemical tests showed excellent rate performance(40C,80 mAh g^-1)and cycle stability（1200 cycles,81%）.（2）Using Na₃（VOPO₄）₂F@rGO as the positive electrode,full batteries were assembled with the commercial activated carbon and the sodium titanate array negative electrode,respectively.Since the activated carbon negative electrode exhibits a lower initial coulombic efficiency and poor rate performance,the assembled sodium ion hybrid capacitors’performance is not very good and needs further optimization.The performance of the sodium titanate array is optimized by both carbon coating and usage of ether electrolytes.The test results showed that the rate and cycle performance（over 10,000 cycles）of both Na₃（VOPO₄）₂F@rGO positive electrode and sodium titanate negative electrode in the ether electrolyte NaPF₆/DIGLYME have been greatly improved.The assembled full battery exhibited high energy density(166.3 Wh kg^-1),high power density(7166.4 W kg^-1)and good cycle stability（90%after 1100 cycles）.