XRD study on the electrochemical hydriding/dehydriding behavior of the La–Mg–Ni–Co-type hydrogen storage alloys
XRD study on the electrochemical hydriding/dehydriding behavior of the La–Mg–Ni–Co-type hydrogen storage alloys
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DOI：
10.1016/j.jallcom.2005.04.195
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发表时间：
2005-11
影响因子：
6.2
通讯作者：
Yongfeng Liu;H. Pan;M. Gao;Y. Lei;Qidong Wang
中科院分区：
文献类型：
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作者：
Yongfeng Liu;H. Pan;M. Gao;Y. Lei;Qidong Wang
采用X射线衍射（XRD）分析方法系统研究了由PuNi 3型菱方结构的（La，Mg）Ni 3相和CaCu 5型六方结构的LaNi 5相组成的La-Mg-Ni基合金La 0. 7 Mg 0. 3（Ni 0. 85 Co 0. 15）3. 5的电化学充放氢行为。结果表明，合金的PuNi 3型菱方结构和CaCu 5型六方结构在放氢/脱氢过程中仍保持不变。对于所研究的合金，LaNi 5相由于良好的表面电化学活性而首先被分解，并且在非常初始的电化学充电过程中为（La，Mg）Ni 3相提供氢。此外，可以清楚地注意到，对于（La，Mg）Ni 3相和LaNi 5相，在包埋/放氢过程中，α相和β相之间的晶胞体积膨胀存在很大差异，即，离散的晶胞体积膨胀，其覆盖了总晶胞体积膨胀的大部分。因此，离散的电池体积膨胀而不是总电池体积膨胀被认为是形成缺陷结构和随后的合金颗粒的粉碎所必需的，这导致在电化学充电/放电循环期间较大的容量劣化。提出了一个示意性模型，详细描述了脱氢/脱氢过程中的α-到β-相变。
Electrochemical hydriding/dehydriding behavior of the La–Mg–Ni-based alloy La0.7Mg0.3(Ni0.85Co0.15)3.5consisting of a (La,Mg)Ni3phase with the PuNi3-type rhombohedral structure and a LaNi5phase with the CaCu5-type hexagonal structure was systematically investigated by means of X-ray diffraction (XRD) analyses. The results indicate that the PuNi3-type rhombohedral structure and the CaCu5-type hexagonal structure of the alloy are still preserved during hydriding/dehydriding process. For the alloy studied, the LaNi5phase was first hydrided due to good surface electrochemical activity for decomposing water and provides hydrogen to the (La,Mg)Ni3phase in the very initial electrochemical charging process. Moreover, it is clearly noted that, for both the (La,Mg)Ni3phase and LaNi5phase, there is a large difference in the cell volume expansion between the α- and β-phase during hydriding/dehydriding process, that is, a discrete cell volume expansion, which covers most of the total cell volume expansion. Therefore, the discrete cell volume expansion rather than the total cell volume expansion is believed to be essential for the formation of defect structures and, subsequently, for the pulverization of the alloy particles, which leads to the larger capacity degradation during electrochemical charge/discharge cycling. A schematic model is proposed to illustrate in detail the α- to β-phase transition during hydriding/dehydriding process.