Abstract
AB2型Laves phase合金具有優異的儲氫量及吸氫速率等特性，適合作為鎳氫二次電池的負極材料。本實驗將實驗計劃法得到的 Ti0.35Zr0.65Ni0.6V1.4 以Mn置換部分V並適當調整比例，希望找到具單純結構和優異電容量的合金組成，藉無電鍍鎳表面處理改善合金抗腐蝕能力及提高合金高速放電容量，並探討無電鍍鎳對電極電化學性質的影響。從合金性質的實驗結果的分析，我們發現添加Mn有助於合金結構的純化，使合金具有C14型式六方(hexagonal)結構。將Ni化學計量提高至1.0和1.2，Mn化學計量定為0.2和0.4，我們找到較佳的負極材料Ti0.35Zr0.65Ni1.2Mn0.2V0.6 其放電容量在310mAh/g附近，放電時電壓保持平穩，並且合金具有相當優異的放氫能力。經由表面無電鍍鎳處理後合金會保有高電容量的原有特性，且具有優異的高速放電能力及抗腐蝕能力。鎳鍍層良好抗腐蝕能力能有效增長電池循環壽命並且在過放電期間提供良好防護能力使電極免於過度氧化所造成的電容量損失。此外，我們發現電極高速放電能力與電極表面催化活性有關：電極催化活性（交換電流值）愈高，其高速放電能力愈佳。相對於 Ni-P鍍層而言，純Ni鍍層能提供電極較佳的催化活性。但合金粉末在純Ni電鍍期間，由於在鹼性環境中合金活性表面產生氧化層，造成電極需要相當長的活化過程。而Ni-P鍍層合金所需活化次數較少，但其高速放電能力較純Ni鍍層合金差。在合金粉末上先施以Ni-P表面無電鍍處理再鍍上純Ni鍍層能兼具兩種鍍層之長而互補其短；即保有純Ni鍍層合金優異的高速放電能力和具有Ni-P鍍層合金快速的的活化能力。The P-C-T curves and electrochemical properties of Laves phase(AB2) hydrogen storage alloy based on Ti0.35Zr0.65Ni0.6V1.4alloy by partial substitution or addition with Mn wereexamined. Besides, the electrochemical performances of AB2-type hydrogen storage alloy (Ti0.35Zr0.65Ni1.2V0.6Mn0.2)modified by electroless Ni-P and Ni coatings in acidhypophosphite and hydrazine baths, respectively, have beeninvestigated . It was found that the addition of Mn into theoriginal alloy contributed toward the uniformity of alloyexhibiting a C14 hexagonal structure. Based on theexperimental results, the composition Ti0.35Zr0.65Ni1.2V0.6Mn0.2 with large hydrogen storage and good reversibility forhydrogen desorption is recommended. We also found thatelectrochemical properties of the modified electrodes includinghigh rate dischargeability, cycle life, retaining ability fordischarge capacity during overdischarge, and electrocatalyticactivity for hydrogen electrode reaction were improved bysurface modification. The high rate dischargeability of thealloy coated with Ni in the hydrazine bath was better than thatcoated with Ni-P in the acid hypophosphite bath, but theactivation cycles needed for reaching maximum capacity of theNi coated electrode were four times as long as those coatedwith Ni-P. A compound nickel coating method was thereforedeveloped. The compound nickel coated alloy ( i.e., alloyfirst coated with Ni-P and then with Ni ) retained thecharacteristics of better high rate dischargeability but neededfewer activation cycles when compared with Ni coated alloy.