| 摘要: | 由於鋁資源豐富、便宜易得、對環境友善、低燃燒性等優點，使得可充放電式鋁電池近年來的研究蓬勃發展。但是常用的鋁電池電解液卻對水氣高度敏感同時又較強的腐蝕性。為了解決以上的問題，本研究利用 4-ethylpyridine形成 4-ethylpyridine/AlCl3離子液體作為鋁電池的電解液。實驗系統地研究了不同莫耳比例下的AlCl3與4-ethylpyridine形成的電解液對於電極的充放電性能的影響，在 25 mA/g下，石墨電極的最大電容量為 95 mAh/g，經過 1000 圈循環充放電之後，電容量維持在初始值的 85%左右。另外， 4-ethylpyridine/AlCl3 離子液體對於常見的 Al、 Cu、 Ni、碳纖維紙基材都展現了較低的腐蝕性。當將電池暴露於空氣環境下，電池的充放電電容量只略微低於在 N2氛圍手套箱中的數值，在 100 圈後，電容維持率有 75%。
實驗的第二部分主要針對軟碳、硬碳、活性碳以及有序中孔碳 CMK-8對於 AlCl4?離子的儲能進行討論，系統地研究了不同碳材的結晶度、 比表面積以及孔洞尺寸對於儲能機制的影響。由於軟碳以及硬碳為非理想的石墨結構並且比表面積較小，因此具有較差的充放電性質，其中軟碳的結晶性高於硬碳，所以電化學性能略高於硬碳。而比表面積較大的活性碳以及 CMK-8 在 300 mA/g 下的電容值分別為 59.0 以及 100.5 mAh/g。孔洞的大小以及
幾何結構在電化學行為中也扮演者十分重要的角色。 CMK-8 的骨架不僅可
以提供電子的傳導路徑，同時相互貫穿的三維開放結構也提供了電解液以及 AlCl4?離子的轉移路徑，因此具有較好的電容值以及循環壽命。研究也通過穿透式電子顯微鏡、能量色散 X 射線譜、X 光粉末繞射以及循環伏安法等分析指明 CMK-8的儲能機制為，在陰離子嵌入嵌出的電化學行為中既有電容效應也有擴散效應。
自放電現象對於電池的實際應用有非常重要的影響，因此實驗的第三部分主要針對鋁電池的自放電現象進行討論，通過對不同的石墨材料自放電行為的研究，即自放電後的平台以及電容量損失， 12 小時後天然石墨的電壓可以維持在 2.16 V，而膨脹石墨只有 2.07 V。 由於膨脹石墨的層間較大
且比表面積較大， 雖然有利於電池的電容值提升但是卻也因此而在高電壓
時難以維持 AlCl4?離子插層，造成較嚴重的自放電現象。無論何種石墨材料，以上平台優先自放電，且幾乎可逆。 本實驗通過 in-situ XRD、 SEM mapping以及 Al 負極的腐蝕現象對自放電機制進行推測。;Rechargeable aluminum batteries (RABs) are extensively developed due to their cost-effectiveness, eco-friendliness, and low flammability and the earth abundance of their electrode materials. However, the commonly used RAB ionic liquid (IL) electrolyte is highly moisture-sensitive and corrosive. To address these problems, a 4-ethylpyridine/AlCl3 IL is proposed. The effects of the AlCl3 to 4-ethylpyridine molar ratio on the electrode charge–discharge properties are systematically examined. A maximum graphite capacity of 95 mAh/g is obtained at 25 mA/g. After 1000 charge–discharge cycles, 85% of the initial capacity can be retained. In situ synchrotron X-ray diffraction is employed to examine the electrode reaction mechanism. In addition, low corrosion rates of Al, Cu, Ni, and carbon-fiber paper electrodes are confirmed in the 4-ethylpyridine/AlCl3 IL. When opened to the ambient atmosphere, the measured capacity of the graphite cathode is only slightly lower than that found in a N2-filled glove box; moreover, the capacity retention upon 100 cycles is as high as 75%. The results clearly indicate the great potential of this electrolyte for practical RAB applications.
The chloroaluminate ion storage properties of various carbonaceous electrodes, namely soft carbon (SC), hard carbon (HC), activated carbon (AC), and ordered mesoporous carbon CMK-8, are investigated. The effects of carbon crystallinity, surface area, and pore size are systematically examined. Due to their non-ideal graphitic structures, the charge-discharge capacities of SC and HC electrodes are unfavorable for practical applications, although SC, with its relatively high crystallinity, outperforms HC. The high-surface-area AC and CMK-8 exhibit reversible capacities of 59.0 and 100.5 mAh/g, respectively, at 300 mA/ g. Pore size and geometry play important roles in determining the electrochemical properties. The CMK-8 framework not only serves as an electronic conduction pathway but also provides interpenetrating three-dimensional open channels for electrolyte accessibility and complex AlCl4 anion transport. The charge storage mechanism of the CMK-8 electrode, confirmed by electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry, has a capacitive contribution and a diffusion-controlled intercalation/deintercalation contribution. Based on this unique mechanism, great rate capability, and excellent cyclability of the CMK-8 electrode are demonstrated.
Self-discharge plays as a critical subject for RABs industrial application. In this work, in order to investigate the phenomenon of RAB self-discharge, two different kind of graphite was used as positive material for comparison. Variations in open-circuit potential of natural graphite and expanded graphite electrode have been investigated as a function of the storage time. The OCP of the natural graphite showed a plateau at about 2.16 V after 12 h, while expanded graphite only maintained at 2.07 V. EG, possessing larger d spacing and higher surface area, will result in more channel, high utilization and thus high specific capacity of electroactive sites, however it is difficult for holding AlCl4 anion at high potential, leading to more serious self-discharge. Almost the self-discharge capacity loss attributed to the upper plateau capacity fading and it could be recovered. The self-discharge mechanism of the graphite electrode was confirmed by electron microscopy, energy-dispersive X-ray spectroscopy, in-situ XRD, and corrosion test of Al anode. |
