热处理对La_(0.63)Gd_(0.2)Mg_(0.17)Ni_(3.1)Co_(0.3)Al_(0.1)储氢合金微观组织和电化学性能的影响

Effects of Annealing Treatment on Microstructure and Electrochemical Properties of La_(0.63)Gd_(0.2)Mg_(0.17)Ni_(3.1)Co_(0.3)Al_(0.1) Hydrogen Storage Alloy

在氩气气氛和1173 K保温条件下对La0.63Gd0.2Mg0.17Ni3.1Co0.3Al0.1储氢合金进行不同时间(t=8～168 h)的热处理,采用电感耦合等离子发射光谱(ICP)、X射线衍射(XRD)、电子探针显微分析方法(EPMA)和电化学测试分析方法对比研究了退火时间对合金显微组织演化和电化学性能的影响。研究结果表明,铸态合金组织由Ce2Ni7型、Gd2Co7型、Pr5Co19型、PuNi3型和CaCu5型相组成,其Ce2Ni7型相的丰度为78.9%,随退火时间的延长,退火合金中Ce2Ni7型相的丰度逐渐增加,当退火时间t=168 h时其相丰度达到94.5%,Ce2Ni7型相结构的晶胞参数和晶胞体积随退火时间增加而减小。电化学测试分析表明,退火合金电极的电化学性能与Ce2Ni7型相的丰度有密切关系,退火时间对合金电极的活化性能影响不大,但合金电极放电容量随退火时间的延长逐渐提高,当t=168 h时,合金电极放电容量达到最大值386.8mAh.g-1;退火时间对合金电极循环稳定性的提高和改善有不同程度的影响,当退火时间t=16～168 h时,经100次充放电循环后,其电极容量保持率S100=90.3%～91.5%。热处理能有效改善合金电极电化学反应的动力学性能,但不同退火时间对合金电极的高倍率放电性能影响不明显。

La0.63Gd0.2Mg0.17Ni3.1Co0.3Al0.1 hydrogen storage alloys were annealed with different time （t = 8 - 168 h） at 1173 K in Ar atmosphere. The effect of annealing time on the microstructure and electrochemical properties were investigated by means of inductive- ly coupled plasma （ ICP）, X-ray diffraction （ XRD）, electron probe micro-analysis （ EPMA ） and electrochemical as-cast measurements. The results showed that the alloy mainly consisted of Ce2Ni7-type, Gd2 CoT -type, PrsCo19-type, PuNi3-type and CaCu5-type phase, the phase abundance of Ce2Ni7-type was about 78.9%. The prolonging annealing time led to increase in CezNi7-type phase abundance and the Ce2NiT-type phase abundance was about 94.5% when t = 168 h. Meanwhile, the crystal cell parameters of Ce2 NiT -type phase decreased with increase of annea- ling time. The electrochemical measurements showed that the electrochemical properties of annealed alloys had close relationship with the phase abundance of Ce2NiT-type, the discharge capacity of the alloys increased with the increase of annealing time, the discharge capacity of the alloys reached 386.8 mAh·g-1 when t = 168 h, and the prolonging annealing time could improve cyclic stability of La0.63 Gd0 2 Mgo. iv Ni3 1 Coo.3Alo. 1 alloy electrodes. After 100 charge-discharge cycles, the discharge capacity retention rate Sj0o was 90. 3%- 91.5% when annealing time as 16 - 168 h. In addition, annealing treatment eould improve dynamic performance effectively while had little effect on high rate discharge ability of the alloys.