Study On Preparation And Modification Of Sodium Vanadium Phosphate Cathode Material

In this study,sodium vanadium phosphate/carbon/carbon composite,sodium vanadium phosphate/nitrogen-carbon/carbon composite and sodium vanadium phosphate/carbon/carbon nanotube composite were modified to synthesize sodium vanadium phosphate/carbon cathode materials.Flexible composite electrodes and soft-coated sodium ion batteries were prepared.The synthesis mechanism,composition and structure of the cathode materials were studied.The influence of electrochemical properties and ion transport mechanism.Specific research contents are as follows:First,sol-gel method was used to synthesize vanadium phosphate/carbon cathode material by carbon coating.The effects of calcination temperature and carbon content on the composition,structure and electrochemical properties of NVP were investigated.The results show that the electrochemical performance of sodium vanadium phosphate/carbon cathode material is the best at the ratio of 750^oC and V:citric acid=2:2.At the current density of 0.1C,the discharge specific capacities are 97.94 mAh g^-1 and 96.24 mAh g^-1,respectively,which are better than those of other contrast samples.By scanning electron microscopy analysis,the surface of sodium vanadium phosphate is porous,which is conducive to the electrolyte into the internal of sodium vanadium phosphate,promote its ion transport,and improve its ion conductivity.Although the synthesis process of organic carbon coating on sodium vanadium phosphate is simple,it has limited influence on the electrochemical performance of sodium vanadium phosphate.To further improve its electrochemical performance,other modification measures are needed.Study on Sodium Vanadium Phosphate/Carbon/Carbon Flexible Composite Electrode and its Full Battery.Sodium vanadium phosphate/carbon/carbon flexible composite cathode was prepared by compounding the above synthesized sodium vanadium phosphate/carbon with filter paper.The effects of different temperature and electrolyte additives on its electrochemical performance were investigated.On the basis of sodium vanadium phosphate/carbon/carbon flexible composite cathode semi-battery,the soft-packed full battery was assembled with graphene/SiC/carbon composite negative electrode,and the growth process of SEI membrane of soft-packed full battery was discussed.The results show that sodium vanadium phosphate/carbon/carbon flexible composite electrode with a thickness of 150 um and 5%FEC in the electrolyte has the best electrochemical performance.The battery exhibits excellent flexibility and electrochemical performance.At a current density of 50 C and 1250 cycles,the capacity of the positive electrode remains at 49.43 mAh-1.This shows that the capacity attenuation rate is 0.0098%at high current density of 150 C.The energy density of FSIFB reaches234.1 Wh kg^-1 at 5C.After 1000 cycles at high current rate of 50C,the specific discharge capacity of FSIFB can still be displayed at 30 mAh g^-1.Sodium vanadium phosphate/carbon/carbon flexible composite electrode exhibits excellent electrochemical performance,which is attributed to its three-dimensional porous structure.As an electronic channel between external circuit and sodium vanadium phosphate powder,it enlarges the contact area with cathode materials.Its resistance is reduced and its conductivity is improved.In addition,the practical application of flexible full battery is also explored.After 1600 bends,the battery still discharges.By exploring the AC impedance at different cycles,the growth law of SEI film was obtained,which laid a foundation for the study of electrochemical reaction kinetics of flexible full cell.Study on sodium vanadium phosphate/nitrogen-carbon/carbon flexible composite electrode and its battery.Using ATP as phosphorus source,sodium source and carbon source,and carbon cloth as carrier,a carbon cloth supported sodium vanadium phosphate/nitrogen-carbon/carbon flexible composite cathode with good electrochemical performance was prepared by hydrothermal treatment and in-situ reaction.Compared with other composite cathodes,the nitrogen-doped sodium vanadium phosphate/carbon composite cathode synthesized on carbon cloth using ATP as template exhibits excellent electrochemical performance.At 0.2C current density,the discharge specific capacity is115.204 mA h g^-1 at 50C current density,and the discharge specific capacity remains at30.00 mA h^-1 after 2000 cycles,and the attenuation rate is only-0.028/cycle.A flexible full cell was made up of three-dimensional hard carbon/carbon composite negative electrode.The electrochemical reaction kinetics of the flexible full cell was studied.The flexible full cell had excellent ionic and electronic conductivity at 0.5C.The specific discharge capacity is 117.6 mA h g^-1.Even after 5000cycle,the capacity fading ratio of0.0055%per cycle.In practical applications,by charging the mobile phone for 8 minutes,the possibility of its application in the mobile phone is tested,which shows that the flexible full battery has important practical application value.Study on Sodium Vanadium Phosphate/Carbon/Carbon Nanotube Flexible Electrode.NVP/C/CNTS composite cathode was prepared by vacuum filtration using sodium vanadium phosphate/carbon as cathode material and carbon nanotubes as carrier.Compared with sodium vanadium phosphate/carbon cathode,the composite cathode has fast charge-discharge performance.At charge-discharge rate of 20C,the specific discharge capacity is 100.359 mAh g^-1,and after 300 cycles,the capacity of the composite cathode does not decrease.The three-dimensional conductive network structure of the film is conducive to electron conduction,rich pore structure is conducive to the diffusion of electrolyte,and can accelerate the diffusion of sodium ions to the surface of the electrode.Therefore,the composite has excellent electrochemical properties.The integrated design of NVP/C/CNTS composite electrodes,no binder and conductive agent are conducive to sodium ion diffusion,which provides a new idea for the development of flexible sodium ion batteries.