Effect Of Y Substitution And Annealing Treatment On Electrochemical Performance Of The La-Mg-Ni System Hydrogen Storage Alloy

Due to possessing a higher electrochemical capacity, La-Mg-Ni system hydrogenstorage alloy with the multiphase structure has become to be one of Ni/MH cellcandidate anode materials, but its cycle stability remains to be further improved. In thispaper, we use thermal treatment to prepare the alloy, and the phase structure of the as-cast and annealed alloys are analyzed by means of X-ray diffraction. Then weinvestigate the electrochemical performances and kinetic characteristics by usingadvanced electrochemical measure method. On the premise of guarantee highcapacity，the results of the study has provided a reliable experimental basis in order tofurther improve the La-Mg-Ni alloy electrochemical performances. And it hasimportant guiding significance for solving the cycle stability from the perspective ofheat treatment.In this thesis, the phase structure and electrochemical properties of La0.8-xYxMg0.2Ni3.35Al0.15(x=0~0.4) and La0.7-xCe0.1YxMg0.2Ni3.35Al0.15(x=0~0.2) system hydrogenstorage alloys with Y partial substation for La and annealed at1173K were investigated.The results of the analyzed phase structure showed that all the alloys consisted of multi-phase structures containing LaNi5,(La, Mg)2Ni7main phases.When Y alternative alloygenerated Ni2Y, Ni3Y phase. The alloy had excellent activation characteristic, and themaximum discharge capacity of the Y added alloys first increased then decreased. Thedischarge capacity of La0.6Y0.2Mg0.2Ni3.35Al0.15、 La0.55Ce0.1Y0.15Mg0.2Ni3.35Al0.15was362.4、396.6mAh·g–1in their respective serious alloys. The Y added had improved thecapacity of retention ratio. Similarly, with the increment of replacement, the dynamiccharacteristics of alloys, such as high rate discharge(HRD) performance and Ac impedancespectroscopy, exchange current density, limit current density and the hydrogen diffusion alsowereroughly rising.According to the electrochemical performance of alloy after alloying element Y,selecting the optimum discharge capacity alloy La0.6Y0.2Mg0.2Ni3.35Al0.15、La0.55Ce0.1Y0.15Mg0.2Ni3.35Al0.15to be treated by annealing. The effects of annealingtechnology on the microstructure and electrochemical performances of the alloys werestudied. The microstructure of alloy still hold multiphase structure after beingannealed，heat treatment can hardly influence the phase structure of alloy, but thediffraction peak intensity of residual phase had reduced. After annealing alloys showed excellent activation performance, the maximum discharge capacity, electrochemicalcycling stability and HRD of the alloy first declined and then elevated with theannealing temperature rising, and the kinetic characteristics had been improvedeffectively. By comparing the electrochemical performance of various temperatureannealed alloys, the appropriate annealing temperature of La0.6Y0.2Mg0.2Ni3.35Al0.15、La0.55Ce0.1Y0.15Mg0.2Ni3.35Al0.15selected1273K and1173K.