近年來能源儲存的技術隨著電動車、綠色能源等發展而備受關注，其中以環境友善、成本低廉的商用鎂合金作為陽極，氧氣還原反應為主的空氣電極作為陰極的鎂空氣電池系統也成為研究的焦點之一。但鎂合金陽極在含水的電解質中腐蝕速率過快，放電時的負差效應(negative difference effect)與塊狀效應(chunk effect)造成陽極效率衰減，無法溶解的放電產物造成放電電壓下降等，皆使得鎂空氣電池的發展與應用受到限制。本論文旨在研究不同商用鎂合金作為陽極，以及採用不同的電解質添加劑，來探討鎂合金陽極在鎂空氣電池中的放電行為，並結合其顯微結構的變化來進行機制上的討論。
第一部分的實驗使用AZ31、WE43和LZ91三種常見商用鎂合金來做為鎂空氣電池中的陽極材料，使用3.5 wt%氯化鈉水溶液作為電解質；而第二部分的實驗則使用WE43鎂合金作為鎂空氣電池的陽極材料，以3.5 wt%氯化鈉水溶液及額外添加0.2 M水楊酸鈉或0.05 M磷酸鈉三種不同成分的水溶液作為電解質。透過量測鎂合金陽極在電解質中的開路電位、電化學阻抗圖譜、動態極化掃描曲線、定電流密度放電表現、放電前後重量改變、氫氣析出體積、電解質成分測定等，來定量鎂合金陽極在該電解質中的抗蝕能力及放電時的陽極性能，並結合光學顯微鏡與掃描式電子顯微鏡/能量散布X光光譜等分析，針對鎂合金陽極放電前後的巨觀和微觀顯微結構與其陽極性能做連結。
在第一部份的實驗中我們發現AZ31鎂合金的放電產物較容易崩裂(breakdown)，因而對應到最嚴重的負差效應；WE43鎂合金則因覆蓋於陽極上的放電產物結構過於緻密，而造成最嚴重的陽極電位損失；LZ91鎂合金不均勻的放電表面則導致最嚴重的塊狀效應。在第二部分的實驗中則發現水楊酸鈉的添加不僅可以抑制WE43鎂合金表面放電產物的生成，進而減少陽極電位損失與負差效應，同時也使合金的放電形貌變得更為均勻，藉此來降低塊狀效應的發生。磷酸鈉的添加則會產生大量磷酸鎂(Mg3(PO4)2)放電產物覆蓋於陽極表面，其鬆散易崩裂的特性雖然同樣減少了陽極電位的損失，但與未添加添加劑相比其導致了更為嚴重的負差效應。
我們可以由兩部分實驗的結果得出，薄或鬆散的放電產物有助於降低鎂合金陽極在放電時的陽極電位，藉此提升電池放電電壓，但若其產生嚴重的崩裂，則會加劇負差效應的發生而使得陽極效率下降；而放電形貌越均勻則塊狀效應越不明顯，進而對應到陽極效率的提升。在本論文中使用WE43鎂合金作為鎂空氣電池陽極，在含0.2 M水楊酸鈉添加劑的3.5 wt%氯化鈉電解質中放電，達到63.3%的陽極效率、1331.8 mAh/g的比容量與1338.7 Wh/kg的能量密度，為本實驗中最佳的陽極放電性能。

In recent years, energy storage technology receives lots of attention with the development of electric vehicles and green energy. Hence, magnesium-air battery systems using environmental-friendly and low-cost commercial magnesium alloys as the anode and the oxygen reduction reaction-based air electrodes as the cathode have become one of the promising energy storage systems. However, the fast corrosion rate of magnesium alloy anodes in aqueous electrolytes, the anode efficiency decay caused by the negative difference effect (NDE) and chunk effect (CE), and the anode potential drop caused by the accumulation of insoluble discharge products, limit the development and applications of magnesium-air batteries. The purpose of this thesis is to study the discharge behavior and performance of different commercial magnesium alloys as anodes in 3.5 wt% sodium chloride (NaCl) electrolytes with different additives and discuss the relationship between the discharge mechanism and microstructure.
In the first part of the experiment, we use three common commercial magnesium alloys, AZ31, WE43, and LZ91, as the anodes in the magnesium-air batteries and 3.5 wt% NaCl solution as the electrolyte; while in the second part of the experiment, we use WE43 magnesium alloy as the anode, and 3.5 wt% NaCl solutions with 0.2 M sodium salicylate (SAL) or 0.05 M sodium phosphate (Na3PO4) additives as the electrolytes. We measure the open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, constant current density discharge curves, weight change before and after discharge, the volume of hydrogen evolved from the magnesium alloy anode, and the composition of electrolytes after discharge, to quantify the corrosion resistance and the discharge performance of magnesium alloy anodes in the electrolytes. Combining with optical microscopy (OM) and scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) analysis, we can link the discharge performance and mechanism of magnesium alloy anode to the macroscopic and microscopic microstructures.
In the first part of the experiment, it is found that the discharge products on AZ31 alloy are prone to breakdown, thus corresponding to the most serious negative difference effect. The dense discharge products on WE43 alloy cause serious anode potential drop. And the uneven discharge surface of LZ91 alloy leads to the most serious chunk effect. In the second part of the experiment, it is found that the addition of sodium salicylate can not only inhibit the formation of discharge products on WE43 alloy, reducing the anode potential drop and negative differential effect, but also make the alloy discharge morphology more uniform and reduce chunk effect. On the other hand, the addition of sodium phosphate results in the formation of magnesium phosphate (Mg3(PO4)2) discharge products on the anode surface. Although its loose and easy-to-breakdown characteristics reduce the anode potential drop, it also promotes the negative difference effect.
From the results of the experiments, we can conclude that thin or loose discharge products can reduce the anode potential drop of the magnesium alloy anode during the discharge process, but the breakdown of the discharge products will aggravate the negative difference effect and cause anode efficiency loss. On the other hand, the more uniform the discharge morphology, the less chunk effect, which corresponds to a better anode efficiency. In this thesis, the best anode performance can be achieved by using WE43 alloy as the anode in a 0.2 M sodium salicylate-added 3.5 wt% NaCl electrolyte, the anode efficiency is 63.3%, the specific capacity is 1331.8 mAh/g, and the energy density is 1338.7 Wh/kg.

摘要..................i
Abstract..................iii
誌謝..................vi
目錄..................vii
圖目錄..................ix
表目錄..................xii
第一章 緒論..................1
第二章 文獻回顧..................3
2.1 鎂空氣電池簡介..................3
2.1.1 鎂空氣電池應用與其運作原理..................3
2.1.2 鎂空氣一次電池所遭遇的問題..................5
2.1.3 負差效應..................6
2.1.4 塊狀效應..................8
2.2 合金微結構對鎂合金陽極放電性質的影響..................10
2.2.1 合金元素添加與二次相的效應..................10
2.2.2 結晶取向與晶粒大小的影響..................12
2.3 鎂空氣電池的電解質添加劑..................13
第三章 實驗方法與步驟..................16
3.1 實驗流程..................16
3.1.1 合金微結構對鎂合金陽極放電行為的影響..................16
3.1.2 不同電解質添加劑對鎂合金陽極放電行為的影響..................17
3.2 電化學量測與陽極放電性能測定..................18
3.2.1 鎂合金陽極試片製備..................18
3.2.2 電解質配製..................18
3.2.3 電化學實驗架構..................18
3.2.4 定電流密度放電測試與陽極性能定量..................20
3.2.5 放電期間之負差效應析氫反應定量..................22
3.2.6 放電期間之塊狀效應定量..................24
3.2.7 放電後電解質中離子含量測定..................24
3.2.8 放電前後之電化學阻抗圖譜與分析..................25
3.2.9 鎂合金陽極放電前後之動態極化掃描曲線..................26
3.3 放電後顯微結構觀察..................27
3.3.1 保留放電產物之試片製備及顯微結構觀察..................27
3.3.2 橫截面試片製備及顯微結構觀察..................27
第四章 合金微結構對鎂合金陽極放電行為的影響..................29
4.1 實驗結果..................29
4.1.1 鎂合金陽極放電前的電化學行為..................29
4.1.2 鎂合金陽極放電過程中的電化學行為與放電性能..................32
4.1.3 鎂合金陽極放電後的電化學行為..................36
4.1.4 鎂合金陽極放電後的顯微結構..................38
4.2 實驗結果討論..................42
4.2.1 鎂合金陽極放電前的電化學行為..................42
4.2.2 鎂合金陽極微結構與放電行為的關係..................44
4.2.3 鎂合金陽極放電後的電化學行為..................47
4.2.4 不同鎂合金作為鎂空氣電池陽極的差異..................48
第五章 不同電解質添加劑對鎂合金陽極放電行為的影響..................51
5.1 實驗結果..................51
5.1.1 WE43鎂合金於具有不同添加劑電解質中放電前的電化學行為..................51
5.1.2 WE43鎂合金於不同添加劑電解質放電過程中的電化學行為與放電性能..................55
5.1.3 WE43鎂合金於不同添加劑電解質中放電後的電化學行為..................59
5.1.4 WE43鎂合金於具有不同添加劑電解質放電後的顯微結構..................61
5.2 實驗結果討論..................65
5.2.1 不同電解質添加劑對WE43鎂合金放電前電化學行為的影響..................65
5.2.2 不同電解質添加劑對WE43鎂合金陽極放電行為的影響..................66
5.2.3 不同電解質添加劑對WE43鎂合金放電後電化學行為的影響..................74
5.2.4 不同電解質添加劑對鎂空氣電池性能的影響..................75
第六章 結論..................77
第七章 未來展望..................79
第八章 參考資料..................80

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