退火温度对La0．8Mg0．2Ni3．3Co0.2Six(x=0、0．1)合金电化学贮氢性能的影响

Influence of annealing temperature on the electrochemical hydrogen storage characters of the La_(0.8)Mg_(0.2)Ni_(3.3)Co_(0.2)Si_x(x=0,0.1) alloys

采用真空感应熔炼制备了La0.8Mg0.2Ni3.3Co0.2Si x(x=0、0.1)电极合金,并将铸态合金进行真空退火处理,退火温度为900、950、1000和1050℃,保温时间为8h。用XRD分析了铸态及退火态合金的相结构,测试了铸态及退火态合金的电化学贮氢性能。结果表明,铸态及退火态合金均具有多相结构,包括两个主相(La,Mg)2Ni7和LaNi5以及一个残余相LaNi3。退火处理未改变合金的相组成,但使两个主相的含量发生明显改变。合金主相的晶格常数及晶胞体积随退火温度的增加而增加。铸态及退火态合金均具有良好的活化性能,第1次循环即可达到最大放电容量。退火处理明显改善了合金的电化学循环稳定性,合金的放电容量随退火温度的升高先增加后减小。合金的高倍率放电性能(HRD)、电化学交流阻抗谱(EIS)以及氢扩散系数(D)的测试表明,合金的电化学动力学随退火温度的升高先上升后降低。

The La0.8Mg0.2Ni3.3Co0.2Six（x=0、0.1） electrode alloys were prepared by using a vacuum induction furnace, immediately, a part of the as-cast alloys was annealed at 900, 950, 1000 and 1050℃ in vacuum for 8h. The phase structures of the as-cast and annealed alloys were checked out by XRD, what was more, the electro- chemical hydrogen storage characteristics of the as cast and annealed alloys were also examined. The results in- dicate that the as-cast and annealed alloys have a muItiphase structure, involving two maior phases of （La, Mg）2Ni7 and LaNi5 as well as a residual phase of LaNi3. There was not any change on the phase composition af- ter annealing treatment, which was opposite to the content of the two major phases, changing a lot. Mean- while, the lattice constants and cell volumes mount up with the growing of the annealing temperature. The as- cast and annealed alloys have a well activation properties, which reaches the maximum discharge capacity at the first cycle. The electrochemical cycle stability was markedly improved by annealing treatment, however, the discharge capacity first mounts up and then goes down with the annealing temperature rising. Which adjust well to the values of electrochemical kinetics by the tests of HRD, EIS and H diffusion coefficient.