宽温型AB5储氢合金结构及其电化学性能研究

用高频感应熔炼法制备了Mm(NiCoAlMn)5储氢合金,采用模拟电池法测试了合金在238～323 K温度范围内的活化、放电容量和高倍率放电性能.结果表明:制备合金为典型AB5型储氢合金,303K温度条件下吸氢量达到1.38％(质量分数),氢化物生成焓为32.36 kJ ·mol-1H2.合金电极的活化性能、放电容量和高倍率性能受温度影响显著.室温预活化可有效改善电极的低温性能,经室温预活化后合金电极在238 K最大放电容量达到336 mAh·g -1,明显高于未经室温预活化的最大放电容量25 mAh·g-1.Mm(NiCoMn)5贮氢合金电极的高倍率性能随着温度的升高先升高后降低,273和303 K温度条件下合金保持高倍率性能良好,3C放电电流密度条件下容量保持率均高于80％；238 K温度条件下合金的大电流放电性能急剧降低,1C放电电流密度条件下容量保持率仅为10％; 273 K下合金电极的综合性能最佳,最大放电容量达到340 mAh·g-1,300 mA·g-1放电电流密度下的高倍率放电比率为86％.循环伏安法测试证实,在238～323 K范围内,电极的氧化峰峰值电流(Ip)与扫描速度的平方根(v1/2)之间均存在良好的线性关系,整个电极反应受氢原子扩散控制；随着温度的降低氢扩散系数急剧下降,从而导致该合金电极的低温高倍率放电性能变差.由Arrhenius公式计算出合金中的氢扩散活化能为10.56 kJ·mol -1.

Structure Characterization and Electrode Properties of AB5 Hydrogen Alloy Suitable for Wide-Temperature Application

Mm(NiCoAlMn)5 alloy was fabricated in arc-melting furnace under argon atmosphere,and its electrochemical properties,including activation,discharge capacity,cycle stability and high rate discharge(HRD),were investigated using simulated battery.The results indicated that the as-prepared alloy belonged to AB5 type structure,its hydrogen capacity was 1.38%(mass fraction) at 303 K,and the enthalpy change in the formation of hydride was 32.36 kJ · mol-1 H2.The electrochemical properties of the alloy electrodes were mainly affected by temperature.Pre-activation for these samples under room temperature enhanced their low-temperature properties.The maximum discharge capacity of the alloy electrode reached 336 mAh · g-1 at 238 K if an additional pre-activation process was applied,which was evidently higher than that without pre-activation,25 mAh · g-1.The high rate dischargeability fluctuated with increasing test temperature.When tested at 273 and 303 K,both the alloy electrodes exhibited good high rate dischargeabilities,which were more than 80% while the discharge current density of less than 3 C.However,the high rate dischargeability decreased rapidly at 238 K,which was only 10% at discharge current density 1C.A better performance was observed in 273 K,where 340 mAh · g-1 of maximum capacity,86% of high rate discharge(HRD300) was obtained.Cyclic voltammetry tests showed that it had a good linear relationship between the oxidation peak current(IP) and the square of voltage scanning speed(ν1/2),suggesting that electrode reaction was controlled by diffusion process.The hydrogen diffusion coefficient decreased sharply with decreasing temperature,followed by a poor HRD performance at low temperature.The activation energy for hydrogen diffusion in Mm(NiCoAlMn)5 alloy electrodes was calculated to be 10.56 kJ · mol-1H2,using the Arrhenius equation.