Abstract
以AB2置換型鋯錳鎳基合金作為鎳氫電池負極材料，具有優異的放電容量。但是實驗發現，經過多次的充放電後，其循環壽命會衰減得很嚴重。在本實驗中藉由添加少量的鉻、鈷來研究並改善電化學行為。此外，由ZrMn0.6V0.2Co0.1Ni1.2合金的第二相和經熱處理的表面鍍鎳層，研究其對電化學充放電特性的影響。合金以電弧法熔煉製得，其錠塊以機械法粉碎，部份合金粉末(-100進行恆溫氣相吸放氫P-C-T實驗，另一部份粉末(<325 mesh)先予以表面無電鍍鎳，而後加入約3%鐵弗龍(PTFE)黏結劑，鋪在鎳網上冷壓成負極板。另外，以氫氧化鎳Ni(OH)2為正極板，尼龍不織布(nonwoven nylon cloth)為分隔層，在電解液30%KOH+1%LiOH中進行充放電實驗。由實驗結果發現:添加少量的鉻或鈷合金仍具有C15型式立方結構，其中添加鉻可得較佳充放電壽命，但會使氣相平衡氫氣壓上升，使得電容量減少。若在合金中添加鈷，可得穩定的電化學行為；以鈷取代部份的鎳，除可保持高電容量外，循環壽命會有一些改善。合金的第二相藉由強酸的侵蝕後，在電化學實驗中，需要較長的活化循環次數，來達到穩定電容量，因此合金中的第二相可幫助電極的活化。本實驗亦發現，鎳在充放電過程中大量的被溶解出來，藉由表面鍍鎳層熱處理方式，對充放電循環壽命的改善助益不大，且處理溫度愈高放電容量愈差。The cyclelife of AB2 metal hydride electrode based on Zr(Mn-Ni)system is usually less than that of the Cd electrode used forNi/Cd batteries. In this study, an alloy ZrMn0.6V0.2Co0.1Ni1.2modified with Cr and Co was investigated. In addition, theeffect of secondary phases and Ni coating layer on theelectrochemical characteristics was also examined. XRDpatterns, SEM and OM morphologies, the P-C-T curves, and theelectrochemical characteristics were established. It was foundthat the alloys substituted or added with some Cr or Co couldimprove their cycle life. Corrosion/oxidation and dissolutionof the electrode caused the degradation of the electrochemicalperformance. Besides, some Ni was dissolved from the Nicoating on ZrMn0.6V0.2Co0.1Ni1.2. Heat treatment was conductedto reduce the degree of dissolution of Ni. However, the cyclelife was not improved much. Therefore, corrosion/oxidation wasthe main cause for the decay of ZrMn0.6V0.2Co0.1Ni1.2electrode. Secondary phases are dispersed in the ZrMn0.6V0.2Co0.1Ni1.2 alloy matrix. In the electrochemical test,activation process was related to the presence of thesesecondary phases. Furthermore, pretreatment with acid did notreduce the activation time, because newly oxidized surface wasformed after the pretreatment.