| Sodium-ion batteries(SIBs)have become one of the research hotspots in the field of secondary battery due to its abundant sodium resources,good safety and low cost.Sodium vanadate(Na3V2(PO4)3)has become one of the main cathode materials for SIBs due to its high theoretical specific capacity,high working voltage,good structural stability and high sodium ion conductivity.However,the intrinsic electronic conductivity of Na3V2(PO4)3 is low,its electrochemical performance needs to be improved.Carbon coating is proved to be an effective method to improve the sodium storage performance of Na3V2(PO4)3.However,the current preparation methods of Na3V2(PO4)3/carbon composites are complex and poorly controllable.Here,we employ organic phosphonic acids as multifunctional raw materials for constructing nitrogen doped carbon coated Na3V2(PO4)3 with high performance sodium storage properties.The main work as follows:1.In this chapter,we successfully developed a feasible method for preparing Na3V2(PO4)3/N-doped carbon composites by appiying nitrilotrimethylene triphosphonic acid(ATMP)as a multifunctional raw material.Well-defined Na3V2(PO4)3particles are encapsulated in a N-doped carbon matrix,which enables the fast sodium ion and electron transport.Among all the samples,Na3V2(PO4)3/N-doped carbon composite obtained under 850?shows the best sodium storage performance.Its reversible charge/discharge capacities after 100cycle are as high as 101.4/101.6 m Ah g-1 at 1 C,which are maintained at100.5/100.4 m Ah g-1at 5 C.Moreover,it shows attractive long-term cycling performance with a capacity rention of 90.1% after 600 cycles at 5 C.This strategy is expected to facilitate the effective construction of Na3V2(PO4)3/carbon compositrs for large-scale production applications.2.Citric acid-organophosphonic acid is combined with the sol-gel method to prepare an NVP/NC composite material with a 3D interconnected porous framework.Due to the high adhesion and high ductility of citric acid,it can promote the growth of the inorganic NVP phase on the carbon skeleton,and at the same time can improve the compatibility between the active material and the conductive matrix.Moreover,its cross-linking properties during the esterification reaction help the 3D interconnected carbon skeleton tend to be nano/micron.In this chapter,trisodium citrate is used to replace sodium hydroxide to provide the sodium source.In nanostructured NVP/NC composite materials,firstly,nanocrystals can shorten the transmission distance of sodium ions;secondly,it can reduce the transfer barrier of sodium ions and promote structural strain porous framework structure;finally,the continuous carbon framework produces a percolating 3D conductive network.The data shows that the sodium vanadium phosphate synthesized based on ATMP does not have a significant decrease in capacity after 4000 cycles at a rate of 10 C,which is very attractive for its application in large-scale energy storage.3.Organic phosphonic acid and organic cross-linked citric acid combined with spray drying technology to prepare Na3V2(PO4)3/NC composite material with hollow microsphere structure.Scanning images confirmed that the sample with the highest tap density of hollow microsphere morphology was successfully construct.Thanks to the combined effects of multiple modification methods,the overall electrochemical performance of the NVP/NC-800 microsphere electrode is very attractive.First cycle discharge specific capacity is as high as 104.2 m Ah g-1at 10 C,and capacity retention rate of 85.3%after 1000 cycles..It provides a choice for realizing the commercial application of NVP cathode materials in sodium ion batteries. |
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