Study On The Preparation And Electrochemical Properties Of NaVPO₄F Cathode Material For Sodium Ion Battery

In recent years,the performance of lithium-ion battery?LIBs?is much higher than that of sodium-ion battery,so the research of sodium-ion battery has been delayed for a long time.However,recent research results show that the price of lithium metal increases rapidly because of the shortage of lithium resources,which greatly increases the raw material cost of lithium-ion batteries and limits the further research and development of lithium-ion batteries.At this time,sodium ion battery?SIBs?as a new alternative to lithium battery energy storage system gradually entered the eyes of people.Sodium resources are very rich,and sodium and lithium elements belong to the same main group,and have similar chemical properties,which makes the corresponding Na-based electrode materials have good electrochemical properties.Among them,polyanion cathode materials have attracted more and more attention because of their stable crystal structure and high working voltage.In addition,polyanionic materials have the advantages of simple synthesis process,high theoretical capacity and good crystallinity.Of course,polyanionic materials can not be ignored shortcomings,that is,low conductivity.This also limits the further development of polyanionic materials as sodium cathode materials.In order to improve the properties of the materials,carbon-coated or ion-doped materials are usually used to improve the properties of the materials.In this paper,carbon-coated NaVPO₄F composites were synthesized by high-temperature solid-state method.The morphology,structure and electrochemical properties of the composites were characterized,and the materials were studied in depth.The results show that the navpo4f carbon composites have the first turn current density of 122 mAh g^-11 at 0.1 C current density,and the capacity retention rate is 86.9%after 100 cycles.In addition,At the current density of 1 C,the material still exhibits 80 mAh g^-1 capacity.On the one hand,the presence of fluoride ion improves the voltage platform of the material,on the other hand,the coating of carbon elements makes the navpo4f composite have good cycle performance and ratio performance.Of course it can not be denied that NaVPO₄F carbon composites still have a lot of room for improvement.In order to further improve the properties of the materials and optimize the morphology of the materials,the freeze-drying preparation method was designed in this paper.In this paper,two-carbon composite NaVPO₄F composites?NVPF/C/rGO?were successfully designed and prepared by freeze-drying method.Electrochemical tests showed that both PVP and rGO had a certain effect on the improvement of the performance of the material,and the discharge capacity of the first turn increased from 51 mAh g^-1 to 81 mAh g^-1and 82 mAh g^-1,respectively.The double carbon composite NVPF/C/rGO has the best electrochemical performance,and its first discharge capacity is up to 118 mAh g^-1,which indicates that the composite with two carbon sources,PVP and rGO,has the best electrochemical performance,and the first cycle discharge capacity is up to 118 mAh g^-1.The double-carbon composite NVPF/C/rGO still has a specific capacity of 65 mAh g^-1 at a current density of 10 C.In addition,the electrochemical properties of the materials with different contents of PVP and rGO were also compared,and the optimal addition of PVP and rGO was obtained.In addition,the results of EIS and GITT test show that the NVPF/C/rGO material with the best performance also has excellent dynamic properties.