镁含量对RE-Mg-Ni系A_2B_7型储氢合金结构与性能的影响

Influence of Magnesium Content on Structure and Performance of A_2B_7-type RE-Mg-Ni Hydrogen Storage Alloys

采用感应熔炼方法制备了La0.8-xGd0.2MgxNi3.1Co0.3Al0.1(x=0,0.1,0.15,0.2,0.25,0.3,0.4)储氢合金,并在氩气气氛和1173 K下进行退火处理.合金相结构分析结果表明,镁含量(x)较低时合金以Ce2Ni7型为主相结构,A2B7型相丰度(Ce2Ni7+Gd2Co7)达到98.8%;镁含量较高时合金相由A2B7型、CaCu5型和PuNi3型物相构成,随着镁含量的增加,PuNi3型和CaCu5型相组成逐渐增多,其晶胞参数随Mg含量的增加而减小,同时合金的吸氢平台也随之升高.电化学测试结果表明,随着合金中Mg含量增加,合金电极的最大放电容量和循环稳定性均呈先增大后减小的规律,其中x=0.15时合金电极具有最高的电化学放电容量(393 mA.h/g)和最佳的循环寿命(S100=92.82%).合金电极的高倍率放电性能(HRD)随Mg含量的增加先减小再增大然后又减小,适量的Mg元素改善了合金电极的动力学性能.

La0.8-xGd0.2MgxNi3.1Co0.3Al0.1（x=0,0.1,0.15,0.2,0.25,0.3,0.4） alloys were prepared by induction melting followed by annealing treatment at 1173 K for 8 h in Ar atmosphere. Phase structure analyses show that main phase is the Ce2Ni7-type phase and the phase abundance of Ce2Ni7- and Gd2CoT-type is 98.8% at the lower Mg content. When x≥0. 25, the alloys are mainly composed of A2BT-type, CaCus-type and PuNi3-type structure. The phase abundance of the PuNi3- and CaCu5-type phase increase with the high content of Mg. The unit cell parameters of main phases decrease and hydrogen absorption plateau rises with the increasing content of Mg. Electrochemical measurements show that as the Mg content increases, the discharge capacity and cyclic stability of alloy electrodes both first increase and then decrease. La0.65 Gd02 Mg0 15＂ Ni3.1CO0 .3A10.1 alloy electrode exhibits the maximum electrochemical discharge capacity （393 mA h/g） and the best cyclic stability（ S100 = 92.82% ）. The high rate dischargeability first decreases then increases and final decreases. The appropriate Mg content improves electrochemical kinetics property of alloy electrodes.