热处理温度对La-Y-Ni合金相结构和电化学性能的影响

采用磁悬浮感应熔炼法制备了组分为LaY_2Ni_(9.7)Mn_(0.5)Al_(0.3)的合金,在不同温度(1 073～1 373 K)下对合金进行热处理,利用X射线衍射法(XRD)、电子探针(EPMA)和电化学性能测试等方法,系统地研究了热处理温度对合金相结构和电化学性能的影响。结果表明,热处理可以显著提高合金的相均匀度,随着热处理温度的升高合金中的主相Ce_2Ni_7相先增加后减少。电化学研究表明,合金电极的最大放电容量、倍率性能和循环稳定性随着热处理温度的升高均呈现先升高后降低的趋势,与Ce_2Ni_7相含量的变化一致。电化学压力-组成-温度(P-C-T)测试表明,合金具有2个放氢平台,且随着热处理温度的升高合金的放氢坪台压增加。当热处理温度为1 273 K时,合金的Ce_2Ni_7相含量最高为86.53%(w/w),电化学性能最佳,最大放电容量为386.80 mAh·g~(-1)(60mA·g~(-1)),在电流密度为900 mA·g~(-1)时的高倍率性能HRD_(900)=89.45%,循环300周后的容量保持率S_(300)=72.18%(300 mA·g~(-1))。

Effect of Annealing Temperature on Structure and Electrochemical Properties of La-Y-Ni Alloy

The LaY₂Ni_9.7Mn_0.5Al_0.3 alloy was prepared by magnetic suspension induction melting method. It was annealed at different temperatures from 1 073 to 1 373 K. The effect of annealing temperature on the phase structure and the electrochemical properties was systematically investigated by X-ray diffraction (XRD), electron probe micro analysis (EPMA), and electrochemical measurements. It was proved that the heat treatment significantly improved the phase uniformity of the alloy. The content of the main phase Ce₂Ni₇-phase increased first and then decreased with the annealing temperature. At the same time, the maximum discharge capacity, high rate discharge-ability and the cyclic stability of the alloy electrodes all increased first and then decreased, which were consistent with the change of the content of Ce₂Ni₇ phase. The electrochemical pressure-content-temperature (P-C-T) curves of the alloy electrodes had two hydrogen desorption platforms, and their pressures both increased with the annealing temperature. When the annealing temperature was 1 273 K, the Ce₂Ni₇ phase content of the alloy was 86.53%(w/w), and the electrochemical properties were the best. The maximum discharge capacity reached to 386.80 mAh·g^-1 (60 mA·g^-1), the high rate discharge-ability at current density of 900 mA·g^-1 (HRD₉₀₀) was 89.45%, and the maximum capacity retention after 300 cycles (S₃₀₀) was 72.18% (300 mA·g^-1).