简介概要

La_0.8-xRE_xMg_0.2Ni_3.2Co_0.6储氢合金的结构及电化学性能

来源期刊：中国有色金属学报2005年第7期

论文作者：唐睿刘丽琴柳永宁于光朱杰武刘晓东

文章页码：1057 - 1061

关键词：镍氢电池；储氢合金；稀土；放电容量

Key words：nickel-metal hydride battery; hydrogen storage alloy; rare earth; discharge capacity

摘要：通过感应容炼制备了La_0.8-xRE_xMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0 ≤x ≤ 0.3) 合金。采用X射线衍射分析了该合金的晶体结构，并研究了其电化学性能。结果表明: 该合金是由LaNi₅主相和LaNi₃第二相构成; 随着Sm(Dy)取代La量的增加，合金主相单胞体积线性收缩，合金储氢量和放电容量减小，当Sm(Dy)取代量分别为0.1、 0.2、 0.3时，合金容量由380 mA·h/g分别减小到370(362)、 355(334)、 329(295) mA·h/g，但高倍率放电能力和循环稳定性得到改善， 100次循环后的容量损失率由20%分别降低到18%(17%)、 16%(14%)、 13%(11%)。

Abstract: La_0.8-xRE_xMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3) alloys were prepared by inductive melting. The crystal structure of the alloys was determined by X-ray powder diffractrometry and the electrochemical properties were investigated. The results show that the alloys are composed of LaNi₅ as matrix and LaNi₃ as secondary phase. With the increasing Sm (Dy) substitution for La, the unit cell volume of matrix of the alloys shrinks linearly and both the hydrogen storage capacity and discharge capacity decrease. When the Sm (Dy) substitution (x value) is 0.1, 0.2 and 0.3, the discharge capacity decreases from 380 mA·h/g to 370(362), 355(334) and 329(295) mA·h/g, respectively. However, the rate performance and cycle stability is improved. After 100 cycles, the capacity loss decreases from 20% to 18%(17%), 16%(14%) and 13%(11%).

文章编号: 1004-0609(2005)07-1057-05

La_0.8-xRExMg_0.2Ni_3.2Co_0.6储氢合金的结构及电化学性能

唐睿¹, 刘丽琴¹, 柳永宁¹, 于光¹, 朱杰武¹, 刘晓东²

(1. 西安交通大学金属材料强度国家重点实验室, 西安 710049;

2. 陕西省锅炉压力容器检测所, 西安 710049)

摘要: 通过感应容炼制备了La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0 ≤x ≤ 0.3) 合金。采用X射线衍射分析了该合金的晶体结构, 并研究了其电化学性能。结果表明: 该合金是由LaNi₅主相和LaNi₃第二相构成; 随着Sm(Dy)取代La量的增加, 合金主相单胞体积线性收缩, 合金储氢量和放电容量减小, 当Sm(Dy)取代量分别为0.1、 0.2、 0.3时, 合金容量由380mA·h/g分别减小到370(362)、 355(334)、 329(295)mA·h/g, 但高倍率放电能力和循环稳定性得到改善, 100次循环后的容量损失率由20%分别降低到18%(17%)、 16%(14%)、 13%(11%)。

关键词: 镍氢电池; 储氢合金; 稀土; 放电容量中图分类号: TG139.7

文献标识码: A

Structure and electrochemical properties of La_0.8-xRExMg_0.2Ni_3.2Co_0.6 hydrogen storage alloys

TANG Rui¹, LIU Li-qin¹, LIU Yong-ning¹, YU Guang¹, ZHU Jie-wu¹, LIU Xiao-dong²

(1. State Key Laboratory for Mechanical Behavior of Materials, Xian Jiaotong University, Xian 710049, China;

2. Shaanxi Measurement Institute for Boiler Pressure Vessel, Xian 710049, China)

Abstract: La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3) alloys were prepared by inductive melting. The crystal structure of the alloys was determined by X-ray powder diffractrometry and the electrochemical properties were investigated. The results show that the alloys are composed of LaNi₅ as matrix and LaNi₃ as secondary phase. With the increasing Sm (Dy) substitution for La, the unit cell volume of matrix of the alloys shrinks linearly and both the hydrogen storage capacity and discharge capacity decrease. When the Sm (Dy) substitution (x value) is 0.1, 0.2 and 0.3, the discharge capacity decreases from 380mA·h/g to 370(362), 355(334) and 329(295)mA·h/g, respectively. However, the rate performance and cycle stability is improved. After 100 cycles, the capacity loss decreases from 20% to 18%(17%), 16%(14%) and 13%(11%).

Key words: nickel-metal hydride battery; hydrogen storage alloy; rare earth; discharge capacity

以储氢合金作为负极活性材料的镍氢电池由于具有能量密度高、高倍率放电能力强、循环寿命长、无记忆效应以及无环境污染等诸多优点, 近年来发展很快。目前达到产业化水平的储氢电极合金主要是AB₅型稀土镍系合金, 文献报道的容量一般为300~330mA·h/g, 经300周次充放电循环后可保持最大容量的70%~80%^[1-3]。与AB₅型稀土镍系合金相比, Zr系合金、 Mg基合金以及V基固溶体合金具有更高的容量, 但他们都存在着各自的缺点: Zr系合金的活化性能较差, 且成本较高; Mg基合金及V基固溶体合金的循环寿命很低, 一般几十次循环后容量就已衰减殆尽。最近, 一类新型的稀土镁镍系合金, 如La_0.7Mg_0.3Ni_2.8Co_0.5、 La_0.8Mg_0.2Ni_3.2Co_0.6等, 引起了人们的关注, 其放电容量高达380~410mA·h/g, 但循环稳定性较差^[4-16], 因而还不能作为镍氢电池的负极活性材料。目前, 通过调整上述新型合金中的稀土组成, 用Ce、 Pr或Nd等原子半径较小的稀土元素部分取代La, 可减轻合金充放电循环时的粉化, 其中用Ce部分部分取代La还可减轻合金在碱液中的腐蚀, 从而改善了合金电极的循环稳定性^{[17, 18]}。然而, Pr或Nd的加入对合金循环稳定性的改善有限^[17], Ce的加入虽然改善效果显著, 但由于在碱液中合金电极表面会形成一致密且不溶的CeO₂钝化膜, 使得电极放电容量有较大减少^{[17, 18]}。为了兼顾合金电极的放电容量与循环稳定性, 本文作者选用原子半径更小且氧化物在碱液中可溶的Sm、 Dy部分取代La_0.8Mg_0.2Ni_3.2Co_0.6合金中的La, 并对新合金的结构和电化学性能进行了研究。

1 实验

La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金采用氩气保护下感应熔炼的方法制得, 所用的单质金属纯度均在99.9%以上。将熔炼好的合金取出后, 机械粉碎并过筛(孔径〈106μm)。

合金的相结构采用D/max-3A型X射线衍射仪(Cu Kα辐射)来测试。

取10g合金粉放入Sievert仪器中, 先进行3次吸、放氢循环使其充分活化, 然后测试合金的压力—容量—温度(p—c—T)曲线。

取0.5g合金粉, 加入2%(质量分数)乙炔黑并混合均匀, 然后加入5%PVA溶液, 搅拌均匀后涂抹到泡沫镍(3cm×4cm)上, 于353K下真空(1×10^-2Pa)干燥, 最后滚压成0.5mm厚的工作电极极片。正极采用广东江门长顺化工有限公司所产Ni(OH)₂粉末, 制造工艺流程与工作电极相同, 只是粘接剂采用30%聚四氟乙烯溶液。正极的设计容量为工作电极的4倍, 电解液采用6mol/L KOH溶液。合金电化学性能的测试在DC-5电池性能测试仪上进行。充、放电制度为: 活化及放电容量测试, 100mA/g充4h, 然后以100mA/g电流放电至截止电位1.0V; 倍率放电能力测试, 100mA/g充4h, 然后分别以100、 300、 600、 900和1200mA/g电流放电至截止电位1.0V; 循环性能测试, 300mA/g充1.3h, 然后以300mA/g电流放电至截止电位1.0V; 每次充、放电结束后均停止20min。

2 结果与讨论

2.1 La_0.8-xRExMg_0.2Ni_3.2Co_0.6合金的晶体结构

图1所示为La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金的X射线衍射谱。从图1可看出, 这些合金具有相同的相组成, 它们都是由具有CaCu₅型结构的LaNi₅主相和具有PuNi₃型结构的LaNi₃第二相构成。合金主相的单胞尺寸如表1和图2所示。随着Sm(Dy)取代La量的增加, 合金主相单胞沿a轴和c轴都产生线性收缩, 单胞体积也呈线性减小, 这是由于Sm(Dy)的原子半径小于La的原子半径而造成的; 然而, 由于单胞沿c轴的收缩要小于沿a轴的收缩, 因而使单胞轴比c/a呈线性增加。从表1和图2还可看出, Dy对合金单胞尺寸的影响大于Sm, 这是因为其原子半径比Sm更小。

图1 La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金的X射线衍射谱

Fig.1 XRD patterns of La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3) alloys

图2 La_0.8-xRExMg_0.2Ni_3.2Co_0.6

Fig.2 Unit cell dimensions for matrix of La_0.8-xRExMg_0.2Ni_3.2Co_0.6

表1 La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金主相的晶体学数据

Table 1 Crystallographic data for matrix of La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3) alloys

2.2 La_0.8-xRExMg_0.2Ni_3.2Co_0.6合金的气相储氢特性

图3所示为La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金在室温(298K)下的吸放氢p—c—T曲线。从图3可看出, 随着Sm(Dy)取代La量的增加, 合金的储氢量减小, 当Sm(Dy)取代量分别为0.1、 0.2、 0.3时, 合金的储氢量由1.6%(质量分数)分别减小到1.57%(1.55%)、 1.53%(1.5%)、 1.48%(1.43%)。然而, 合金吸放氢的平台压力却呈现上升趋势, 这是由于Sm(Dy)取代La导致合金主相的单胞体积减小所致。研究表明^[19]: 储氢合金单胞体积的减小将增大合金吸放氢过程中的晶格体积变形和晶格应变能, 从而使合金吸放氢反应的平台压力增加。

图3 La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金的吸放氢 p—c—T 曲线

Fig.3 p—c—T curves of La_0.8-xRExMg_0.2Ni_3.2Co_0.6

2.3 La_0.8-xRExMg_0.2Ni_3.2Co_0.6合金的电化学性能

图4所示为La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金电极放电曲线。随着Sm(Dy)取代La量的增加, 电极放电容量减小, 当Sm(Dy)取代量分别为0.1、 0.2、 0.3时, 电极容量由380mA·h/g分别减小到370(362)、 355(334)、 329(295)mA·h/g, 这是由于它们的储氢量减小所致。

图4 La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金放电曲线

Fig.4 Discharge curves of La_0.8-xRExMg_0.2Ni_3.2Co_0.6

图5显示了La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金电极的倍率放电能力(用电极在不同放电电流下的放电容量与在100 mA/g下的容量之百分比来表示)。随着Sm(Dy)取代La量的增加, 电极高倍率放电能力提高, 当Sm(Dy)取代量分别为0.1、 0.2、 0.3时, 电极在放电电流为1200mA/g时的高倍率放电能力由38%分别提高到40%(42.5%)、 44%(46%)、 49%(53%)。由于Sm(Dy)取代La导致合金主相的单胞体积减小, 从而使合金放氢的平台压力身高, 合金氢化物的稳定性减小, 放氢过程变得更加容易, 因而合金电极的高倍率放电能力得到改善。

图5 La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金电极放电能力

Fig.5 Rate discharge ability of La_0.8-xRExMg_0.2Ni_3.2Co_0.6

图6所示为La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金电极的循环稳定性。随着Sm(Dy)取代La量的增加, 电极循环稳定性提高, 当Sm(Dy)取代量分别为0.1、 0.2、 0.3时, 100次充放电循环后的容量损失率由20%分别降低到18%(17%)、 16%(14%)、 13%(11%)。一般认为, 在合金电极循环过程中, 合金氢化而引起的体积变化与吸氢量成正比。由于Sm(Dy)取代La导致合金吸氢量减少, 使得合金氢化时的体积变化减小, 从而减轻了合金的粉化, 改善了合金电极的循环稳定性。

图6 La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金电极循环稳定性

Fig.6 Cycle stability of La_0.8-xRExMg_0.2Ni_3.2Co_0.6

3 结论

1) La_0.8-xRExMg_0.2Ni_3.2Co_0.6(RE=Sm, Dy, 0≤x≤0.3)合金是由LaNi₅主相和LaNi₃第二相构成。随着Sm(Dy)取代La量的增加, 合金主相单胞沿a轴和c轴都产生线性收缩, 单胞体积也呈线性减小, 但单胞轴比(c/a)线性增加。

2) 随着Sm(Dy)取代La量的增加, 合金储氢量和放电容量减小, 当Sm(Dy)取代量分别为0.1、 0.2、 0.3时, 容量由380mA·h/g分别减小到370(362)、 355(334)、 329(295)mA·h/g, 但高倍率放电能力和循环稳定性得到改善, 100次循环后的容量损失率由20%分别降低到18%(17%)、 16%(14%)、 13%(11%)。

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收稿日期: 2004-12-22; 修订日期: 2005-04-18

作者简介: 唐睿(1976-), 男, 博士.

通讯作者: 唐睿, 博士; 电话: 029-82669071; 传真: 029-82663453; E-mail: cqhj@mail.xjtu.edu.cn

(编辑陈爱华)

简介概要

详情信息展示

La_0.8-xRExMg_0.2Ni_3.2Co_0.6储氢合金的结构及电化学性能

Structure and electrochemical properties of La_0.8-xRExMg_0.2Ni_3.2Co_0.6 hydrogen storage alloys

相关论文

相关知识点

简介概要

详情信息展示

La0.8-xRExMg0.2Ni3.2Co0.6储氢合金的结构及电化学性能

Structure and electrochemical properties of La0.8-xRExMg0.2Ni3.2Co0.6 hydrogen storage alloys

相关论文

相关知识点

La_0.8-xRExMg_0.2Ni_3.2Co_0.6储氢合金的结构及电化学性能

Structure and electrochemical properties of La_0.8-xRExMg_0.2Ni_3.2Co_0.6 hydrogen storage alloys