稀土系过化学计量比贮氢合金Re（NiMMn）_5+X的组织及电化学性能

【作者】 单丹丹；

【导师】 罗永春；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2004， 硕士

【摘要】 为了提高AB₅型贮氢电极合金在市场中的竞争力，满足我国Ni／MH电池产业的发展及贮氢电极合金对更高的性能价格比的要求，本文确定以研究和优化AB₅型低成本无Co贮氢电极合金为目标，采用过化学计量比、高温长时间均匀化退火、合金成分优化的方式对合金相结构及电化学性能的影响规律进行深入的分析和讨论。力求提高合金的综合电化学性能，为开发低成本长寿命稀土系贮氢电极合金奠定基础。根据文献报道[13]，本课题拟选用LaNi_4.75Mn_1.25作研究的基础成分，在该合金成分的基础上，通过采用1273K 168h的退火处理、合金优化、降低合金计量比的办法改善合金的综合电化学性能。并对合金的组织结构的变化，合金元素对电化学性能影响规律做以分析和总结。 LaNi_4.75Mn_1.25高温退火合金及快凝合金的中子衍射及电化学行为表明，Mn元素在晶体结构中通过两种占位方式影响合金电极的循环稳定性；①形成2c哑铃占位②3g位置的占有状况，在一定范围内3g位置占有数增大时有利于合金电极的稳定性。 过化学计量比合金电极的容量主要与过化学计量比大小，3g位置上替代元素的种类和数量有关。一方面计量比增大，合金结构中2e位置哑铃结构数增加，这样会减少氢原子在6m间隙位置的占有数；另一方面，合金优化后由于原子尺寸差异、合金元素电子结构以及合金吸放氢热力及学动力学性能的变化均会对合金电极的容量产生影响。 对合金B端元素的优化结果表明，采用少量的非Co过渡族金属Cu、Fe、Cr、Sn替代LaNi_4.75Mn_1.25合金中的Ni能有效改善合金的电化学循环稳定性但个别合金的电化学容量有所降低。而使用这些元素用来替代合金中的Mn元素会明显降低合金的电化学循环稳定性。但使合金的活化性能及循环初始容量有所改善。采用Ce、Nd、Pr替代LaNi_4.75Mn_1.25合金A端的La元素有助于提高合金综合电化学性能。Ce、Nd在提高基础合金的循环稳定性方面表现突出而Pr在对合金的容量方面影响作用大。 对LaNi_4.68Mn_0.93合金电化学性能的测试表明，降低LaNi_4.75Mn_1.25合金计量比能够提高合金的电化学活化和循环容量。对LaNi_4.48Cu_0.2Mn_0.93合金电化学性能的测试表明，通过降低合金过化学计量比，使用少量B端Cu元素优化的方式可以得到综合电化学性能较好的合金。更多还原

【Abstract】 To improve the competition ability of AB5 type hydrogen storage electrode alloy in the market, meet the need of the Ni/ MH battery industry’s development of our nation and the need for high cost performance of Ni/MH electrode alloy, this paper will lays emphasis on investigating Co-free hydrogen storage alloys and optimizing its composition. By means of over stoichiometry, composition optimization, keeping annealing at high temperature for long time, the effects of the composition on phase structure and electrochemical properties were studied systemically so as to improve the comprehensive electrochemical properties. According to reference [13], LaNi4.75Mn1.25 was choosed to be our basic composition. Through the method of 1273K 168h annealing treatment, composition optimization and reducing stoichiometry ratio of alloys, the feasibility of improving the alloy’s comprehensive electrochemical properties was investigated.Neutron diffraction and electrochemical behavior of LaNi4.75Mn1.25 annealing and quenching alloys showed that the element Mn in the alloy may influence the electrochemical cycle stability of metal hydride electrode by occupying two atom site in the lattice: (1) dumbbells pairs of B-type atoms occupying the atom site 2e (2) occupation of atom site 3g , increase in amount of Mn at 3g site will do good to the cycle stability of metal hydride electrode in some extent.The capacity of over stoichiometric metal hydride electrodes is in relationship with the extent of over-stoichiometry, the atom sort and its amount. On the one hand, the amount of dumbbell pairs of B-type atoms will decreases the amount of H atom occupying interstitial site 6m; on the other hand , the difference of atom size, the influence of electron structure of alloying elements, the variation in thermodynamics and kinetics of absorption and desorption processes will all affect the electrochemical capacity.The experimental result of optimizing B-type elements of the alloy indicated using less transition elements (Cu, Fe, Cr, Sn) to substitute for Ni of alloy LaNi4.75Mn1.25 improved the cycle stability of metal hydride electrode, but some of them suffer from decrease of electrochemical capacity. Meanwhile, when using these alloying elements to substitute for element Mn will reduce the cycle stability of metal hydride electrodes greatly, but increase the maximum cycle capacity of hydride electrodes. The experimental result also indicated when substituting Ce, Pr, Nd.for Ni will improve the comprehensive electrochemical performances. Ce, Nd can benefit the cycle stability of the hydride electrodes, while Pr can improve the electrochemical capacity of hydride electrodes.The result of electrochemical measurement of LaNi4.68Mn0.93 indicated decrease in the stoichiometry of LaNi4.75Mn1.25 can increase the electrochemical capacity. The electrochemical performances of LaNi4.48Cuo.2Mn0.93 indicated that adopting lowerstoichiometry and less B-site element such as Cu substituting for Ni of LaNi4.75Mn1.25 could achieve better comprehensive electrochemical properties.更多还原