| Summary: | 碩士 === 國立中央大學 === 材料科學與工程研究所 === 103 === This study is based on chemical reduction method, using of supercritical carbon dioxide technology to production of tin dioxide and Carbon nanocomposites, and applied as an anode material for the sodium-ion battery. With supercritical high diffusivity, surface tension approaches zero, etc., to improve the dispersibility of tin dioxide on Graphene and observed the electrochemical properties.
The experimental results show that the supercritical prepared of tin dioxide (SnO2-SC) compare the traditional atmospheric synthesis (SnO2-air) has small nanoparticles shows a reversible capacity of 95 mAh/g (at 0.02 A/g). Adding Garphene and Carbon nanotubes as to enhance its electrical conductivity and as the buffer. The carbon nanotubes (SnO2-CNT20wt%-SC) only can up to 149 mA/g. The grapheme (SnO2-G20wt%-SC) shows a clearly higher capacity of 275 mAh/g as same condition, and also enhance the high-rate capacity, it is due to Graphene has high electrical conductivity and surface active position. And with buffer of Graphene can effectively suppress the volume expansion, and uniformly dispersed in supercritical exhibits a capacity retention ratio of approximately 66 % after 100 cycles.
In order to study the added amount of the carbon and the critical temperature (Tp) and critical pressure (Tc) impact electrochemical performance, this study was to use 10 wt.%, 20 wt.%, 35 wt.% different carbon content were analyzed and electrochemical tests.The experimental results that 35 wt.% has better stability, but its reversible capacity were not very high, the amount of 20 wt.% have good reversible capacity and a smaller amount of life decline. Change the Tp and Tc were be relatively close to the supercritical density and it will affect the state of the supercritical fluid. The results shows that high supercritical density have more high solubility, but the diffusion coefficient decreases, the electrochemical results
also show the 145 bar, 80°C has batter capacity and stable cycle performance. iii
Electrolyte were to affect the capacity and stability, in our results show the ionic-liquid has batter cycle stability with a capacity retention of 100% after 100 cycles, but the relatively capacity were small. Although, PC-FEC has the good capacity, but the cycle performance were unstable.
Finally, in order to study the reason of capacity why different to theoretical capacity, we use the Ex-siut EXAFS and Ex-situ XRD to observe the sodiation/desodiation reaction, electrode to charge on 0.01V and analysis by HRTEM. The results shows the conversion reaction was observed. But not form the final Na15Sn4 phase. Therefore, the capacity can’t not be achieved to the theoretical capacity.
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