Structure and Electrochemical Properties of La-Y-Ni Based A2B7-type Hydrogen Storage Alloys with Magnesium Doping
Mg-containing La1.9-xYxMg0.1Ni6.48Mn0.32Al0.2(x=0～1.8)and Mg-free La0.8Y1.2Ni6.48Mn0.32Al0.2 A2B7-type al-loys were prepared by powder metallurgy sintering,the effects of Mg doping and Y content on the phase consti-tutes,crystal structure and electrochemical properties of the alloys were investigated.The results show that an appropriate increase of Y content is beneficial to the formation of single phase with 2H-Ce2Ni7 type for the Mg-containing alloys.Mg and Y atoms preferentially occupy the[A2B4]subunit,the cell parameters a,c,and Vcell of the 2H-Ce2Ni7-type main phase and the volume difference ΔVd between the V[[A2B4]and V[AB5]units volume grad-ually decrease with increasing Y content,however,the Vcell and ΔVd of 2H-Ce2Ni7 type phase for x=1.8 and Mg-free alloys are relatively high.The reversible hydrogen release performance and electrochemical properties of the alloys are closely related to the Y content and ΔVd.The electrochemical properties of the Mg-containing alloys are better than those of the Mg-free alloy with the same Y content,where x=1.0～1.2 Mg-containing alloys have smallerΔVd and the best electrochemical properties,resulting in the maximum discharge capacity of 375 mAh·g-1,with remaining capacity retention rate S100 of 91％after 100 charge/discharge cycles,and the high rate discharge per-formance HRD900 is～80％at a discharge current density of 900 mA·g-1.Thus,the electrochemical properties of La-Y-Ni system A2B7 type alloys can be significantly improved by doping Mg and optimizing Y content.
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