AB_(3.8)型La_(0.75)Mg_(0.25)Ni_(3.3)Co_(0.5)储氢合金颗粒度对其电化学性能的影响

Effects of Particle Size of AB_(3.8)-type La_(0.75)Mg_(0.25)Ni_(3.3)Co_(0.5) Alloy on Its Electrochemical Performances

采用筛分法测试了La0.75Mg0.25Ni3.3Co0.5储氢合金粉的粒度分布。结果表明,随着合金颗粒度减小,相应颗粒度的合金含量(质量分数)几乎呈线性增加,从合金颗粒度为58μm时的21%增加到38μm时的29%。同时,选用不同颗粒度的La0.75Mg0.25Ni3.3Co0.5合金粉制备了储氢合金电极,研究了合金颗粒度对储氢合金电极的活化性能、最大放电容量、放电特性以及循环稳定性的影响规律与机制。研究表明,合金颗粒度的大小对合金电极的活化性能基本无影响,合金电极均具有好的活化性能,经1至2个循环后达到最大放电容量。随着合金颗粒度的减小,合金电极的最大放电容量持续增加,从合金颗粒度为58μm时的332.5 m Ah·g-1增加到38μm时的最大值342.9 m Ah·g-1;放电中值电位先降低后升高,由合金颗粒度为58μm时的1.0302 V减小到45μm时的0.9825 V,然后增加到38μm时的1.0141 V;容量衰减速度呈现出先变慢后加快的变化规律。综合比较,在合金颗粒度为48μm时,La0.75Mg0.25Ni3.3Co0.5储氢合金电极展示了最佳的综合电化学性能,电化学性能的改善主要归因于合金电极电荷转移速度的加速和内阻的减小。

The particle size distribution of La0.75Mg0.25Ni3.3Co0.5 alloy was measured by means of sieving method. The re- sults show that the content of alloy （ weight percentage） for the corresponding particle size almost increases linearly with the decreasing of particle size for La0.75Mg0.25Ni3.3Co0.5 alloy powders,and the content of alloy increases from 21% to 29 % when the particle size ranges from 58μm to 38 μm. Moreover, the La0.75Mg0.25Ni3.3Co0.5 metal hydride electrodes were prepared with alloy of different particle sizes. The effects of particle size on the activation performance, maximum discharge capacity, discharge potential characteristic and cycle stability of the alloy electrodes were investigated. The mechanisms of the effects of the particle size on the electrochemical properties of electrodes were also discussed in detail. The results indicate that the particle size has no effect on the activation performance of the electrode. All alloy electrodes have excellent activation capabilities, and the maximum discharge capacities can be obtained within only one or two cycles. The maximum discharge capacity increases continuously with the decreasing of particle size. And the maximum discharge capacity increases from 332.5 mAh · g^-1 （58 μm） to 342.9 mAh · g^-1 （38μm）. The middle voltage in discharge curve firstly decreases and then increases. The middle voltage in discharge curve decreases from 1.0302 V （58 μm） to 0.9825 V （45 μm） ,and then increases to 1. 0141 V （38 μm）. The velocity of decay for discharge capacity firstly decelerated and then accelerated. Overall, the alloy with particle size of 48 μm exhibits the best electrochemical properties. The improvements of the electrochemical properties are attributed to the increase of the charge - transfer reaction rate on the alloy and the decrease of the internal resistance of the electrode.