Study On The Microstructure And Electrochemical Properties Of The La_2-xSm_xMg₁₆Ni(x=0.1?0.4) Hydrogen Storage Alloys Composite With Ni And Graphene

The problem of environmental pollution has become more and more serious,so the country has begun to vigorously develop new energy.La₂Mg₁₆Ni hydrogen storage alloy has the advantages of no pollution and high capacity.It has become a candidate material for the negative electrode material in the new energy Ni-MH battery,but it has defects in electrochemical performance.In this paper,the electrochemical performance and dynamic performance of La₂Mg₁₆Ni alloy are improved by the methods of element substitution,addition of additives,and mechanical ball milling multiple modifications.First,La_2-xSm_xMg₁₆Ni(x=0.1?0.4)alloy was smelted in an intermediate frequency vacuum induction melting furnace,La_2-xSm_xMg₁₆Ni(x=0.1?0.4)alloy were added with100 wt.%Ni powder and 5 wt.%graphene,and then ball milled for 10 hours to make a composite hydrogen storage alloys.The microstructure of the composite hydrogen storage alloy was analyzed by XRD and SEM.It is found that the main phase of the composite hydrogen storage alloy is the Ni phase,and the secondary phases are the La₂Ni₃ and La₂Mg₁₇phases.The composite hydrogen storage alloy powder has obvious agglomeration.Tests on the electrochemical and dynamic properties of the alloy show that the substitution of the Sm element can improve the electrochemical and dynamic properties of the alloys.When the substitution amount of Sm is 0.3,the maximum discharge specific capacity of the alloy is 88.7mAh/g,and the capacity retention rate S₅₀ of the alloy is 73.63%.With the increase of Sm element substitution,the high-rate discharge,limiting current density I_L,and hydrogen diffusion coefficient D of the composite hydrogen storage alloy electrode increase first and then decrease.When the substitution amount of Sm x=0.3,the maximum values are:HRD₁₅₀₀=28.55%,I_L=1754mA/g,D=1.86*10^-10cm²,and the minimum charge transfer resistance Rct in EIS is 0.791?.Secondly,the microstructure,electrochemical performance and dynamic performance of the composite hydrogen storage alloy prepared after 10h ball milling of La_1.7Sm_0.3Mg₁₆Ni+100 wt.%Ni+y wt.%graphene(y=0,3,5,10)hydrogen storage alloy were studied.The results show that the addition of graphene does not change the phase composition of the alloy.The alloy phases are Ni,La₂Ni₃ and La₂Mg₁₇ phases.At the same time,after EDS surface scanning analysis,it was found that graphene was attached to the surface of the alloy particles.In addition,TEM analysis found that the addition of graphene which hinders the amorphization process during the ball milling process.When the amount of graphene added is 10 wt.%,the maximum discharge specific capacity of the alloy is 100.6mAh/g,and the maximum limiting current density I_L is 2002mA/g.The capacity retention rate of the alloy increases first and then decreases with the addition of graphene.It is the largest when the addition amount of graphene is 5 wt.%,S₅₀=73.62%.The alloys high rate performance,charge transfer resistance Rct and hydrogen diffusion coefficient D are best when the graphene content is 5 wt.%.Finally,the effects of different milling times(10h,20h,30h)on the microstructure,electrochemical properties and kinetic properties of the hydrogen storage alloy La_1.7Sm_0.3Mg₁₆Ni+100 wt.%Ni+10 wt.%graphene were studied.The results show that with the increase of ball milling time,the alloy particles begin to be refined and accompanied by agglomeration.Increasing the ball milling time is helpful to the amorphization of the alloy.The performance of the alloy is improved with the increase of ball milling time.When the ball milling time is 20h,the alloy has the best electrochemical and dynamic properties.The maximum discharge specific capacity is182.5mAh/g,and the S₅₀ capacity retention rate is 70.05%.With the increase of ball milling time,the charge transfer resistance Rct of the alloy decreases sharply,and the charge transfer resistance Rct is 0.259?at 20h.At the same time,the limiting current density I_L,hydrogen diffusion coefficient D,and high rate discharge performance of the alloy reached the best after 20 hours of ball milling,respectively:I_L=2370mA/g,D=1.34*10^-10cm²/s,HRD₁₅₀₀=34.31%.