Element Substitution and Electrochemical Performance of La-Mg-Ni Based Hydrogen Storage Alloys for Automotive Batteries
A kind of hydrogen storage alloy of La0.7R0.1Mg0.2Ni3.35Al0.15(R=La/Nd/Sm)was synthesized with induction melting method,and the effect of La substituted with rare earth element Nd/Sm on the phase structure,microstructure,and electrochemical performance of the hydrogen storage alloy was explored.The results show that the substitution of Nd or Sm for La doesn't change the phase composition of the hydrogen storage alloy,which is still composed of LaNi5,(LaMg)2Ni7,and(LaMg)5Ni19 phases,but leads to higher abundance of LaNi5 and(LaMg)5Ni19 phases,and lower abundance of(LaMg)2Ni7 phase in the hydrogen storage alloy.The hydrogen storage alloy,with La,Nd and Sm as R,deliver the maximum discharge capacities of 377 mAh/g,382 mAh/g and 376 mAh/g,respectively,after the second charge-discharge cycle.With La substituted with Nd or Sm,the hydrogen storage alloy has its high-rate discharge capacity,the charge retention rate after 24 hours,and capacity retention rate after 100 cycles all improved to some extent,among which the hydrogen storage alloy with Nd as R is the best in all corresponding performance.Moreover,the substitution of La with Nd or Sm can make the hydrogen storage alloy with higher exchange current density and higher coefficient of hydrogen diffusion.Its high-rate discharge performance,exchange current density and hydrogen diffusion coefficient are all in in the same trend,indicating that high-rate discharge performance of the hydrogen storage depends on both exchange current density and hydrogen diffusion coefficient.
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