Research Of Novel Phosphate As Cathode Materials For Sodium Ion Battery

Among energy storage technology, secondary battery is of great significance inenergy storage and conversion. Lithium ion batteries currently occupy the main market forportable mobile electronic devices, and is rapidly developing to the hybrid electricvehicles market, which will lead to greatly increase of the demand of lithium, however,Lithium resources are very limited on the earth. Based on the present situation and thedemand, abundant sodium entered people’s field of vision, lithium and sodium are in thesame group with similar chemical properties. The potential of Na+/Na is2.71V vs. thestandard electrode potential, and theoretical specific capacity of Na is1166mAh/g. S Thecontent of sodium in the earth’s crust is much higher than lithium and the ocean containshuge amounts of sodium, refining of sodium is straightforward. Therefore, sodium ionbatteries will be a very promising energy storage technology.In this article, we chose Na4Co3(PO4)2P2O7and Na3V2(PO4)3as the research object,preparing Na4Co3(PO4)2P2O7/CNTs by a sol-gel method and characterizing itselectrochemical properties when it’s used as a cathode of sodium ion battery. Resultsshowed that carbon nanotubes can from a continuous electrically conductive networkbetween active materials which greatly increased the electrical conductivity ofNa4Co3(PO4)2P2O7. At1C,5C,10C,20C, the reversible capacity was80mAh/g,60mAh/g,40mAh/g,30mAh/g respectively, and exhibited a good cycling performance.We synthesized Na3V2(PO4)3/C by a solid phase method and a soft template method,and explored the influence of synthesis conditions on the morphology ofmaterials. Characterizing structure and morphology by X-ray diffraction (XRD) and Fieldemission scanning electron microscopy (FESEM), the results show that the productprepared at800oC had good crystalline, products obtained at lower temperature or forshorter time had poor crystalline or with impurities. In the template synthesis, we can getNa3V2(PO4)3/C composite material with large porous and three-dimensional carbonskeleton at650oC for12h, this framework structure would collapse when we extended timeto14h or increasd temperature to800oC. We prepared Na3V2(PO4)3/C composite material by a template method, andcharacterized its structure and performance by thermogravimetric analysis (TG), Ramanspectroscopy, Field emission scanning electron microscopy (SEM), transmission electronmicroscopy (TEM), X-ray diffraction (XRD), constant current charge-discharge, cyclicvoltammograms. The results showed that the reversible discharging capacity ofNa3V2(PO4)3/C composite material at1C,2C,5C,10C,20C,50C was113mAh/g,100mAh/g,77mAh/g,70mAh/g,62mAh/g and58mAh/g respectively, and coulombefficiency is close to100%. There was hardly capacity attenuation after100cycles at1Cand2C, which showed excellent cycle stability.