| 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 MgTi0.1Al0.1-xPdxNi (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%。... |
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