元素替代对Zr基AB₂型贮氢合金相结构与电化学性能的影响

【作者】 张思方；

【导师】 刘开宇；

【作者基本信息】 中南大学 ， 应用化学， 2008， 硕士

【摘要】 Zr基AB₂型贮氢合金具有放电容量高、循环寿命长等优点,具有较好的应用前景,作为Ni/MH电池的负极材料一直受到广泛的关注。本文首先对贮氢合金的贮氢原理以及对Zr基AB₂型贮氢合金贮氢性能的影响因素做了较为全面的综述。并在此基础上确定以多元合金化为技术路线,利用XRD、SEM、EDX和电化学测试等手段研究替代元素对合金电化学性能的影响及其作用机理。采用元素Ti替代合金ZrCr_0.4Mn_0.4Ni_1.2中的Zr时发现,合金的相结构为C15型Laves相和C14型Laves相以及少量Zr₉Ni₁₁相组成的多相结构。当x=0.1时,合金中C15相的含量达到最大,并随着Ti的掺杂量的增加,C15相逐渐向C14相转变,合金中的非Laves相逐渐减少,并在x=0.4时消失。Ti的掺入有利于C15型Laves相向C14型Laves相转变,并且抑制非Laves相的产生。电化学测试结果表明,加入少量Ti有利于合金活化性能和放电容量的提高,当x=0.1和0.2时,合金电极的活化性能最好,当x=0.1时,合金具有最大放电容量为274mAh/g,并且Ti的掺入有利于合金循环稳定的提高。线性极化、阳极极化、恒电位阶跃和交流阻抗测试表明,随着Ti的掺入量的增加,合金电极的交换电流密度与极限电流密度都是先增加后减小,x=0.1时,合金电极具有最大的交换电流密度和极限电流密度,同时交流阻抗测试也表明,在x=0.1时,合金电极的电化学反应阻抗最小,说明少量Ti的加入有利于合金电极动力性能的提高。在上述研究的基础上,选择综合电化学性能最好的Zr_0.9Ti_0.1Cr_0.4Mn_0.4Ni_1.2为研究对象,采用元素V替代合金中的Cr,系统研究了V的替代对合金Zr_0.9Ti_0.1V_xCr_0.4-xMn_0.4Ni_1.2（x=0～0.3）的电化学性能的影响,结果发现随着V的替代量的增加,合金的活化性能逐渐降低,合金的放电容量则逐渐提高,当x=0.3时,合金具有最大放电容量为314.8 mAh/g。V替代Cr提高了合金的循环稳定性,同时降低了合金的高倍率放电性能。通过P-C-T测试可以看出,随着V替代量的增加,合金的放氢平台压呈下降趋势,合金的放氢容量逐渐增大。线性极化和阳极极化测试结果可以看出,随着V替代量的增加,合金的交换电流密度和极限电流密度按V₀＞V_0.2＞V_0.3＞V_0.1的次序递减,恒电位阶跃测定氢在合金中的扩散系数的变化规律与其一致。通过交流阻抗测试可以看出,随着V替代量的增加,合金电极的反应电阻逐渐增大。更多还原

【Abstract】 Zr-based AB₂ type Laves phase hydrogen storage alloys have been extensively investigated as Ni/MH battery anode material which have good application prospects, because of its much higher discharge capacity and longer life. In this paper, the principle of hydrogen storage alloy and the factors affecting properties of hydrogen storage alloys have been comprehensively reviewed. Based on the review above, multi-component alloying was chosen to research the effect to the properties of hydrogen storage alloys by substituting elements and its mechanism by means of XRD、SEM、EDX and electrochemical methods et al.The effects of substituting Ti for Zr on the phase structures and the electrochemical properties of ZrCro.4Mn_0.4Ni_1.2 have been investigated. The phase structures mainly include C15 Laves phase and C14 Laves phase, with a little second phase Zr₉Ni_<sub>11 in it. When x=0.1, the content of C15 Laves phase reaches maximum. With the content of Ti increasing, C15 Laves phase gradually converts to C14 Laves phase, while the second phase gradually decreasing. When x=0.4, the second phase disappears. The addition of Ti is propitious to convert C15 Laves phase into C14 Laves phase, and inhibit the formation of the second phase. The electrochemical test results show that it is conducive to the activating performance and discharge capacity increase by adding a small amount of Ti in the alloy. When x=0.1 or 0.2, the alloy has best activating properties. When x=0.1, the alloy exhibits the maximum discharge capacity 274 mAh/g. The addition of Ti can elevate the discharge cycle stability of the hydrogen storage alloys. The linear polarization, the anode polarization, the constant potential step and the EIS test show that the exchange current density and the limiting current density first increase then decrease with the content of Ti increasing. When x=0.1, the hydrogen storage alloy electrode exhibit the maximum exchange current density and limiting current density. The EIS test show that the reaction impedance is the minimum among the alloys when x=0.1, which notes that the addition of a small amount of Ti in the alloy electrode is conducive to the improvement of dynamic performance.Choosing Zr_0.9Ti_0.1Cr_0.4Mn_0.4Ni_1.2 alloy as the research object which possesses the best comprehensive electrochemical properties based on the study above. Cr in the alloy was partly substituted by V, and the effect to the electrochemical properties of Zr_0.9Ti_0.1V_xCr_0.4-xMn_0.4Ni_1.2（x=0～0.3）alloys by substitute V for Cr are investigated. It is found that the discharge capacity increases while the activate properties improved with the content of V. When x =0.3, the alloy exhibits the maximum discharge capacity 314.8 mAh/g. It improves the discharge cycle stability by substituting Cr for V, which decreases the high rate discharge ability at the same time. The pressure platform of P-C-T curves decreases during the hydrogen discharge, while the hydrogen discharge capacity increases as the content of V increased. It is found that the exchange current density and the limiting current density descends by V₀> V_<sub>0.2> V_0.3> V_0.1 as the linear polarization and the anode polarization result indicating. The diffusion coefficient tested by the constant potential step basically follows the trends above. The reaction impedance increases with the content of V increasing in the alloy that can be seen from the EIS test.更多还原