錳氧化物超高電容器循環穩定性之研究

本研究主要以定電流充放電、電化學交流阻抗法和感應耦合電漿原子發射光譜法，分析錳氧化物超高電容器之循環穩定性，從實驗結果發現錳氧化物超高電容器之電量衰退隨著電流增加而增加。但當黏著劑含量增加時，此電容在高速充放電下循環一千圈，衰退範圍從原本約30 % 減少到低於5 %，此法可以有效的抑制電量衰退。此外，有兩種機制會造成電量隨著循環次數而衰退。第一種機制是當電極中黏著劑含量較少時，在高速充放電下會造成電極結構的鬆脫。在循環過程中，金屬氧化物與碳黑之間的接觸逐漸惡化，使得電極的電阻逐漸增加，而導致電量的衰退。第二種機制是電極在慢速的充放電下，其界面傳遞的阻力隨著循環次數增加而增加，因而造成電量衰退。在本研究中，有兩種方法可以有效抑制錳氧化物超高電容器在高速充放電循環下的電量衰退。其中一種是將黏著劑含量提高以鞏固電極的結構。另ㄧ種方法是利用SBR去取代PVdF，此乃由於鍵結於金屬氧化物中的SBR可以承受金屬氧化物在循環時的體積變化，使得黏著劑與粒子間的界面不會有過多的應力，因而改善電極結構鬆脫的問題，使錳氧化物超高電容器之循環穩定性大幅提升。

關鍵字

電容；二氧化錳；循環穩定性；水系；氯化鈉

並列摘要

Cycle stability of MnO2·nH2O electrochemical capacitors has been studied by using chronopotentiometry tests, electrochemical impedance spectroscopy (EIS), and inductively coupled plasma-atomic emission spectrometer (ICP-AES). The extent of capacity fading, ranging from ~30 % to < 5 % in 1000 cycles, increases with current-rate and is markedly reduced with increasing binder content. Two fading mechanisms have been identified. With low binder content and at high current-rate, capacity fading occurs in conjunction with appreciable increase in transmission resistance, suggesting progressively deteriorating electric contacts among the pseudocapacitve oxide particles and conductive carbon. The mechanical failure of the electrode structure may arise from the cyclic volumetric variation of the pseudocapacitive oxide particles. On the other hand, increasing interfacial charge-transfer resistance upon cycling has been found to play an important role in capacity fading at low current-rate. In addition, there are two effective ways to suppress capacity fading under high specific charge/discharge current density. One is to use plenty of binder to strengthen the overall structure of the electrode. The other is to use Styrene-butadiene rubber (SBR) to replace Polyvinylidene difluoride (PVdF) as binder component. SBR binder bonded between the oxide particles is rapider to deform in response to the volume change of the oxide particles without introducing excessive stress at the binder-particle interface. Hence, the cycling stability of MnO2·nH2O electrochemical capacitors can be enhanced.

並列關鍵字

capacitor ； MnO2 ； cycling stability ； aqueous ； NaCl

參考文獻

1. R. Kötz and M. Carlen, “Principles and applications of electrochemical capacitors”, Electrochim. Acta, 45, 2483-2498 (2000).

3. B. E. Conway, “Transition from “supercapacitor” to “battery” behavior in electrochemical energy storage”, J. Electrochem. Soc., 138, 1539-1548 (1991).

4. A. J. Bard and L. R. Faulkner, Electrochemical methods: fundamentals and applications, 2nd ed., Wiley, New York (2001).

5. E. Frackowiak and F. Béguin, “Carbon materials for the electrochemical storage of energy in capacitors”, Carbon, 39, 937-959 (2001).

6. B. E. Conway, V. Birss, and J. Wojtowicz, “The role and utilization of pseudocapacitance for energy storage by supercapacitors”, J. Power Sources, 66, 1-14 (1997).

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錳氧化物超高電容器循環穩定性之研究

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