錳鐵氧化物有機超高電容器之製備與分析

Abstract

摘要 藉由計時電位法、循環伏安法和X光吸收光譜，研究分析了錳鐵氧超高電容器在有機電解質中的電化學性質。結晶相的錳鐵氧與碳黑的複合電極在LiPF6有機溶液中可表現出具有120 F/g-MnFe2O4的比電容量。同時，此電容器可以穩定操作在電壓範圍為1.8 V 到 4.2 V(相較於Li/Li+)之間。當工作電壓低於1.8 V時，電容量的衰退速率將會快速增加。從X光吸收光譜的分析來看，衰退機制可能可以歸因於錳鐵氧材料內不可逆的電子結構變化。 在論文的後續部份，分析了一種利用鋰錳氧和錳鐵氧為電極材料的新式混合超高電容器在有機電解質中的特性。結果顯示此系統可表現出良好的電容特性。並且藉由與電池型電極的搭配，使得相較於傳統對稱式電容器，不論在比電容量或是自放電速率皆獲得大幅改善。這樣的混合系統將有助於開發實際應用。

Abstract Electrochemical properties of MnFe2O4 pseudocapacitors in organic electrolytes have been studied via chronopotentiometry, X-ray absorption spectroscopy (XANES) and cyclic voltammetry analysis. Crystalline MnFe2O4 and carbon black composite electrode shows a specific capacitance at least 120 F/g- MnFe2O4 in LiPF6 organic solution. And the capacitor can be safely operated in a potential window between 1.8 V and 4.2 V (vs. Li/Li+). As the working voltage is lower than 1.8 V, the fading rate of the capacitance will rapidly increase. From XANES analysis, the fading mechanism may attribute to the irreversible electronic configuration changes in the ferrite material. At the follow-up part of the thesis, a new hybrid surpercapacitor using LiMn2O4 and MnFe2O4 as the electrode materials in the organic electrolytes is also studied. The results show that this system exhibits good capacitor behavior. By matching with the battery-type electrode, the specific capacitance and self-discharge rate are both improved a lot than symmetric capacitor system. This hybrid system is helpful for developing the practical application.