| With the implementation of the concept of green development,people’s demand for renewable clean energy(such as solar energy,wind energy)keeps rising.In order to improve the utilization rate of these intermittent energy,a large number of energy storage equipment is urgently needed to complete the storage of off-peak energy and the release of stored energy during peak time.Among the numerous energy storage devices,lithium-ion batteries dominate the current market due to their huge performance advantages.However,the market’s demand for energy storage devices is increasing day by day,making it difficult for lithium batteries to meet the demand for large-scale energy storage in the future.Sodium-ion batteries have a similar working principle to lithium-ion batteries.Although the energy density and stability of sodium-ion batteries are not as good as those of lithium-ion batteries,but the huge reserves of sodium on the earth makes sodium-ion batteries have great prospects for large-scale energy storage.As a type of polyanionic cathode material,sodium vanadium phosphate(Na3V2(PO4)3)has a higher theoretical specific capacity(117.5 mAhg-1),a stable charge and discharge platform(3.4V/3.3 V),higher ionic conductivity and good thermal stability,which will make it expected to meet commercial promotion,but the lower electronic conductivity limits its actual rate performance and cycle stability In this thesis,the electrochemical performance of Na3V2(PO4)3 was optimized by means of structural nano modification and carbon coating,and the NVP//NVP symmetrical full battery was successfully constructed.The research results have certain reference significance for promoting the development of sodium ion batteries in the direction of lightness,high safety and high energy density.The main content of the paper is as follows:1.The self-supporting carbon nanofiber network structure was prepared by electrospinning technology,which makes the Na3V2(PO4)3 nanoparticles wrapped in a nitrogen-doped carbon layer and embedded in the carbon nanofibers,thereby obtaining a self-supporting Na3V2(PO4)3 with excellent performance material.This structure improves the electronic conductivity of the material,and the carbon nanofiber network structure as the substrate reduces the quality of the electrode,and also avoids the side reaction between the electrolyte and the metal foil.At the same time,the abundant interstitial network structure increases the penetration of the electrolyte,and also alleviates the volume change during the charging and discharging of the electrode,which effectively improves the energy density,safety and cycle stability of the battery.the reversible capacity of self-supporting Na3V2(PO4)3 positive electrode remains at 102.7 mAhg-1,after 400 cycles at 1 C current density.What is more remarkable is that the average discharge specific capacity of 1000 cycles at 5 C current density can be maintained at about 85 mAhg-1.2.The self-supporting Na3V2(PO4)3 and Na4V2(PO4)3 negative electrode were successfully prepared through the pretreatment process,and the full battery was assembled with self-supporting Na3V2(PO4)3 positive electrode respectively,and showed good electrochemical performance.The capacity retention rate of the Na3V2(PO4)3//Na3V2(PO4)3 symmetrical full battery can be maintained at 82.4%(48.6 mAhg-1)after 100 charge-discharge cycles at 1 C current density,and the average reversible capacity is 45.6 mAhg-1 at 2C current density,both prove that the selfsupporting Na3V2(PO4)3//Na3V2(PO4)3 symmetrical full battery has a good application prospect.In addition,the Na4V2(PO4)3//Na3V2(PO4)3 full battery can also have a high discharge voltage of 3.0 V at a current density of 0.1 C. |
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