【作者】 张彦辉；

【导师】 袁华堂；

【作者基本信息】 南开大学 ， 材料物理与化学， 2009， 博士

【摘要】 Co-非金属化合物,如Co-BN和CoB等在碱液中表现出良好的电化学性能,但该类型材料的电化学反应机理尚不清楚;Mg基储氢合金具有储氢量高、资源丰富和成本低廉等优点是Ni-MH电池潜在的负极材料之一,但合金中Mg的腐蚀导致其电化学循环稳定性较差。针对以上问题和研究现状,本论文研究了Co-非金属化合物Co-Si和Mg基储氢合金两类材料。均匀混合法制备了Co-Si系列材料,考察了它们的结构和电化学性能。研究发现,Co-Si材料中的Co和Si保持着各自原有的晶体结构和形貌;相对于Co和Si,Co-Si材料的电化学性能良好,且Co与Si质量比为4:1时最佳,25mA/g放电电流密度下,最大放电比容量为419.9mAh/g,经过50次充放电循环放电比容量保持在352.2 mAh/g,相应的容量保持率S₅₀为83.9%。熔炼法制备的Co-Si材料分别为Co₂Si、CoSi和CoSi₂合金相,合金的首次放电比容量较低,活化周期较长,但循环稳定性较好,活化后Co₂Si、CoSi和CoSi₂最大放电比容量分别为192.9 mAh/g、173.6mAh/g和176.4mAh/g,经115次充放电循环容量保持率S₁₁₅分别为87.9%、94.8%和92.1%。探讨了CO₂Si合金电极的电化学反应机理,初步推断出合金电极的电化学反应存在吸放氢和氧化还原两个过程,活化前电极存在吸放氢反应,随着循环的进行,合金中的Si慢慢溶解,合金的结构逐渐被破坏,同时Co溶出并发生氧化还原反应,完全活化后电极过程以Co的氧化还原为主。采用机械球磨将机械合金化法制备的CoSi与MgNi合金进行复合制备了MgNi-CoSi复合合金材料,研究并优化了制备条件。结果表明,复合合金为非晶态结构;相对于MgNi合金,复合合金循环稳定性得到提高,并且复合时间为10h,MgNi与CoSi质量比为100:10时达到最佳,经过30周充放电循环容量保持率比MgNi合金提高了35.4%。采用机械球磨将化学还原法制备的NiP和CoP分别与MgNi合金进行复合制备了MgNi-NiP和MgNi-CoP复合合金材料,研究并优化了制备条件。结果表明,复合合金为非晶态结构;相对于MgNi合金,复合合金循环稳定性得到提高;对于MgNi-NiP,复合时间为10h,MgNi与NiP质量比为100:10时其循环稳定性最佳,经过50周充放电循环容量保持率比MgNi合金提高了31.1%;对于MgNi-CoP,复合时间为20h,MgNi与CoP质量比为100:5时其电化学性能最佳,经过50周充放电循环容量保持率比MgNi合金提高了17.2%。机械合金化法成功制备了MgTi_0.1Al_0.1-xPd_xNi（x=0.02-0.08）系列合金,研究了其结构和电化学性能。发现,系列合金主相均为非晶态结构,合金颗粒的形貌和粒径分布相似;当Pd的量为0.06时,合金具有最佳的循环稳定性,25 mA/g放电电流密度下,首次放电比容量为365.2 mAh/g,经过100周充放电循环放电比容量为214.1mAh/g,相应的保持率S₁₀₀为58.6%。更多还原

【Abstract】 The Co-nonmetal composites, such as Co-BN and CoB and so on, have good electrochemical behaviors in alkaline solution, but the electrochemical reaction mechanism of the materials is not understood clearly; Mg-based hydrogen storage alloys is a kind of promising candidate as negative material for Ni-MH batteries because of high capacity, sufficient mineral sources and low cost. However, the practical application is limited because of their rapid degradation during cycle in the electrolyte, which is related to the corrosion of Mg in the alloy. Emerging as the situation requires, the materials Co-Si and Mg-based hydrogen storage alloy were studied in the dissertation.The Co-Si materials were prepared through mixing Co with Si homogeneously. The structural and electrochemical properties of the materials were investigated. It was found that the structures of Co and Si in the Co-Si materials were the same as that of pure Co and Si. Compared with Co and Si, the Co-Si materials had good electrochemical properties, and the Co-Si（4:1） performed the best, at the discharge current density 25 mA/g, whose maximum discharge capacity was 419.9 mAh/g, at cycle 50 the capacity was 352.2 mAh/g and the retention rate was 83.9%. The Co-Si materials prepared by arc-melting were Co₂Si、CoSi and CoSi₂ alloy, respectively. Each alloy had low initial discharge capacity and a long term activation process. After activation, the maximum discharge capacity of Co₂Si、CoSi and CoSi₂ was 192.9 mAh/g、173.6 mAh/g and 176.4 mAh/g, respectively. The alloys showed good cycle stability, the capacity retention rate of which was 87.9%、94.8% and 92.1% at cycle 115, respectively. The electrode reaction mechanism was discussed of the Co₂Si alloy. It was found that the reactions of hydrogen absorption/desorption and Co/Co（OH）₂ coexisted before activation of the alloy, after activation the faradic reaction of Co/Co（OH）₂ was dominant.The MgNi-CoSi composite was prepared by ball milling MgNi with CoSi and the preparation conditions of which were optimized. The results showed that the composite had amorphous structure. Compared with MgNi alloy, the cycle stability of the composite was improved. When the ball milling time was 10 h, the weight ratio of MgNi with CoSi was 100:10, the composite performed the best, at cycle 30 the capacity retention rate was 35.4% higher than that of MgNi.The MgNi-NiP and MgNi-CoP composites were prepared by ball milling MgNi with NiP or CoP synthesized by chemical reduction method and the preparation conditions were optimized. The results showed that the composites had amorphous structures. Compared with MgNi alloy, the cycle stabilities of the composites were improved. For the MgNi-NiP, when the ball milling time was 10 h, the weight ratio of MgNi with NiP was 100:10, the composite performed the best, at cycle 50 the capacity retention rate was 31.1% higher than that of MgNi; For the MgNi-CoP, when the ball milling time was 20 h, the weight ratio of MgNi with CoP was 100:5, the composite showed the best electrochemical behavior, the capacity retention rate of which was 17.2% higher than that of MgNi at cycle 50.The MgTi_0.1Al_0.1-xPd_xNi （x = 0.02 - 0.08） alloys were prepared successfully by mechanical alloying method. The structural and electrochemical properties of the alloys were investigated. The results showed that the main phases of the alloys were amorphous and the images of the alloys were similar. When x = 0.06, the alloy showed the best cycle stability, whose maximum discharge capacity was 365.2 mAh/g, at cycle 100 the discharge capacity was 214.1 mAh/g and the capacity retention rate S₁₀₀was 58.6%。更多还原