微量Mg替代La对低钴快淬AB_5贮氢合金性能的影响

Effects of small amount of Mg substitution for La on properties of low-Co AB_5-type quenched hydrogen storage alloys

用单辊快淬法制备了La0.62-xCe0.27Pr0.03Nd0.08Mgx(Ni0.81Co0.06Mn0.07Al0.06)5.2贮氢合金,采用X射线衍射光谱法(XRD)、场发射扫描电子显微镜(FESEM)、夹片式模拟开口电池测试体系研究了合金的相结构及电化学性能。XRD分析表明,微量Mg(x=0.03)替代La后,合金主相仍为CaCu5型六方结构,同时出现了极微量的A2B7型第二相;使合金的结晶度有所提高,主相晶胞体积V从0.08807nm3降低到0.08792nm3,c/a轴比从0.8082增加到0.8112。电化学性能测试显示,Mg替代La后合金的最大放电容量从329.4m Ah/g(x=0.00)依次降低到313.2m Ah/g(x=0.03),而循环寿命从146周期(x=0.00)明显增加到245周期(x=0.03),主要缘于晶胞c/a轴比增大使吸氢体积膨胀减小进而合金抗粉化能力提高、结晶度提高使合金抗腐蚀能力提高,以及相对较小的贮氢量引起小的晶胞体积膨胀使合金粉化驱动力减小。

The quenched La0.62-xCe0.27Pr0.03Nd0.08Mgx（Ni0.81Co0.06Mn0.07Al0.06）5.2 hydrogen storage alloys were prepared by single-roll rapid quenching.Phase structure and electrochemical properties of these alloys were investigated by means of XRD,FESEM,and ＂sandwich open-air cell＂ testing system.The XRD analysis show that,with Mg substitution for La by 0.03,the trance A2B7-type second-phase appears and the alloy crystallinity is improved,the cell volume V of CaCu5-type main-phase decreases from 0.088 07 nm3（x=0.00） to 0.087 92 nm3（x=0.03） and c/a increases from 0.808 2（x=0.00） to 0.811 2（x=0.03）.The electrochemical results exhibit that maximum discharge capacity Cmax reduces form 329.4 mAh/g（x=0.00） to 313.2 mAh/g（x=0.03）,and cyclelife is extended from 146 cycles（x=0.00） to 245 cycles（x=0.03）.The improvement in cyclelife is attributed to the increased c/a ratio,improved crystallinity,and less hydrogen storage capacity.