镁含量对La1-xMgxNi2．8Co0.7合金性能与结构的影响

Influence of Magnesium Content on Performance and Structure of La_(1-x)Mg_xNi_(2.8)Co_(0.7)(x=0.10～0.25) Alloys

采用XRD分析了La1-xMgxNi2.8Co0.7(x=0.10,0.15,0.20,0.25)合金的晶体结构,研究了合金的气固相储氢特性和电化学性能。结果表明,合金由Ce2Ni7型结构的A2B7主相和少量的具有CaCu5结构的AB5相构成,随Mg含量的增加,合金中AB5相相应减少。合金在吸放氢过程中的熵变ΔS和焓变ΔH与AB5型合金的数值相当。合金的电化学容量随Mg含量的增加,先增大后减小,当x=0.2时合金的容量最大为389.1 mAh.g-1。应当特别指出的是,该类合金表现出良好的低温性能,在温度为233 K时,放电量容量仍有室温时的50%以上。

The effect of Mg content on the crystal structure, thermodynamics and electrochemical prop erties of La1-xMgxNi2.8Co0.7（x = 0.10, 0.15, 0.20 and 0.25） alloys was studied. The phase structures were identified by X-ray diffraction （XRD）. The results showed that all these alloys consisted of two phases： the main phase was the La2Ni7 phase with the Ce2Ni7-type structure and others were LaNi5 with CaCus-type structure. The quantity of the LaNi5 phase decreased with the increasing content of Mg. The properties of hydrogen absorption and desorption weredetermined by pressure-composition isotherms （P-C-T）. The results revealed that the enthalpy change （△H） and entropy change （△S） of these alloys were similar to that of the AB5 systems. The discharge capacity of the alloys first increased and then decreased with increasing x from 0.10 to 0.25. The maximal discharge capacity of the alloys was 389.1 mAh·g^-1 for Mg content of x = 0.2. The low-temperature discharge （LTD） ability of this type alloys was preferable, for example, the discharge capacity of this alloys at 233 K was more than half of that at 293 K.