探討錳鐵氧化物超高電容器在有機系電解液中的速率表現

Study on Rate Performance of MnFe2O4 with Organic Li-Ion Electrolyte

錢人豪(Jen-Hao Chien)

指導教授 ： 吳乃立

國立臺灣大學/工學院/化學工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201602172

摘要

無資料

關鍵字

超高電容器 ； MnFe2O4 ； 有機系電解液 ； 速率表現 ； 能量密度 ； 稀釋

並列摘要

An increasing number of metal oxides exhibiting pseudocapacitive behaviors have been investigated in recent years. We have discovered a nanocrystalline oxide material having the formula of MnFe2O4 that have so far been the only oxide electrode showing pseudocapacitance in both aqueous and organic Li-ion electrolytes. The discovery of this material has opened up the possibility of setting up a high voltage pseudocapacitors of substantially enhanced energy density over the state-of-the-art organic supercapacitors.
In the first part of the thesis, MnFe2O4/CB composite materials have been synthesized via coprecipitation method and followed with a thermal calcination. The electrodes of that composite were tested for the capacitive behaviors in aqueous NaCl solution. For different calcination temperatures, the electrode using MnFe2O4/CB which calcined at 350°C exhibits 63.1 F/g-composite under 10 mV/s scan rate and possesses the largest capacitance compared to the others.
Second, we have explored the spinel-based nanocrystalline ferrite electrodes with various transition metal compositions in organic Li-ion electrolyte. The results indicated that an increment in specific capacitance could be observed with increased concentration of manganese ion. Moreover, an enhanced energy density of MnFe2O4/CB supercapacitor could be obtained by applying the organic Li-ion electrolyte. It displays a substantially higher energy density of 59.6 Wh/kg at a power density of 413 W/kg. Even at a high power density of 16809 W/kg, it still delivers an energy density of 24.3 Wh/kg. The relationship between capacitance and potential window had also been examined and it was found out that more lithium ions could react with the inner surface of manganese ferrite with broader voltage window and thus resulted in a relatively larger pseudocapacitance.
Enhanced rate performance was derived by diluting the concentration of transition metals. The capacitance retentions of MnFe2O4/carbon electrodes are found to be above 60% under 100 mV/s. The superior capability of delivering rather high capacitance under high-power conditions is attributed to the spinel structure formed after lower temperature calcination. Based on our previous study, the pseudocapacitance is predominantly arising from the charge-transfer reaction at the tetrahedral sites of the spinel, balanced by the insertion of cations from the electrolyte.
Besides, the operation voltage window was carefully determined in view of leakage current for the upper voltage limit. On the other hand, the lower voltage limit was selected to maximize the energy density of the spinel oxide electrode.

並列關鍵字

Supercapacitor ； MnFe2O4 ； Organic Li-ion electrolyte ； Rate performance ； Energy density ； Diluted concentration

參考文獻

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