Study On The Microstructure And Electrochemical Properties Of La_2-xPr_xMg₁₆Ni(x=0.1⁰.4) Hydrogen Storage Alloys Composited With Ni And Graphene

La-Mg-Ni hydrogen storage alloy has a large discharge capacity and is widely used as a negative electrode material for nickel-hydrogen batteries,but its poor cycle stability is a key problem that needs to be solved.The electrochemical performance of La-Mg-Ni alloys can be improved through element substitution,mechanical ball milling,and catalyst addition.In this paper,Pr is used to partially replace La in La₂Mg₁₆Ni alloy,La_2-xPr_xMg₁₆Ni(x=0.1,0.2,0.3,0.4)hydrogen storage alloys were prepared by vacuum induction melting,the alloy powder was ball milled with 100 wt.%Ni and different proportions of graphene at different times to obtain ball milled alloys.Analyze the phase composition and microstructure of alloy by XRD/TEM,and the surface morphology and element distribution of the alloys were analyzed by SEM/EDS.The CT2001A electrochemical tester was used to test the discharge capacity,cycle life,and high-rate discharge performance of the alloy.The P4000Princeton electrochemical workstation was used to test the open circuit potential,potential polarization,AC impedance,and hydrogen diffusion coefficient kinetic properties of the alloy.La_2-xPr_xMg₁₆Ni(x=0.1,0.2,0.3,0.4)hydrogen storage alloy as the base alloy,adding 100 wt.%Ni and 5 wt.%graphene ball milling for 10 hours to obtain La_2-xPr_xMg₁₆Ni(x=0.1,0.2,0.3,0.4)+100 wt.%+5 wt.%Graphene ball milled alloys.The effect of different substitution amounts of Pr on the microstructure and electrochemical properties of the alloys was studied.The research results show that each alloy is composed of Ni phase and La₂Mg₁₇ phase,as the amount of Pr substitution increases,the alloy particles are refined.When the substitution amount of Pr is 0.3,the maximum discharge specific capacity of the alloy is 108.4 m Ah/g;when the substitution amount of Pr is 0.4,the cycly stability is 76.13%.In terms of kinetics,as the amount of Pr substitution increases,high rate discharge(HRD),limiting current density and hydrogen diffusion coefficient show the law of first increasing and then decreasing.When the substitution amount of Pr is 0.3,the high-rate discharge performance is the best,the charge transfer resistance on the surface of the alloy electrode is the smallest,the limiting current density is 1834 m A/g,and the hydrogen diffusion coefficient is 1.33×10^-10 cm²/s.The effects of different amounts of graphene on the microstructure and electrochemical properties of La_1.7Pr_0.3Mg₁₆Ni+100 wt.%Ni+y wt.%graphene(y=0,3,5,10)alloys were studied.The research results show that the alloy is composed of Ni phase and La₂Mg₁₇ phase,with the increase of graphene content,the diffraction peak of La₂Mg₁₇ phase gradually broadens,which promotes the formation of nanocrystals.When the graphene is 10 wt.%,the maximum discharge specific capacity of the alloy is 114.7 m Ah/g.Adding an appropriate amount of graphene can improve the dynamic performance of the alloy.When the graphene is 5 wt.%,the electrochemical impedance of the alloy surface is the smallest.The HRD₁₅₀₀,the limiting current density and the hydrogen diffusion coefficient all reach the maximum.Finally,the influence of different ball milling time on the microstructure and electrochemical properties of La_1.7Pr_0.3Mg₁₆Ni+100 wt.%Ni+10 wt.%graphene alloys were studied,the milling time was 10 h,20 h,and 30 h,respectively.The results show that the main phase of the alloys is the Ni phase,as the milling time increases,the La₂Mg₁₇ phase disappears and the Mg₂Ni phase is produced.Ball milling time from10 h to 30 h,the maximum specific discharge capacity of the alloys increases from114.7 m Ah/g to 174 m Ah/g,and the capacity retention rate increases from 66.87%to80.17%.After 30 hours of ball milling.The HRD₁₅₀₀,the limiting current density and hydrogen diffusion coefficient reach the maximum:36.61%,2940 m A/g and9.20×10^-11 cm²/s,respectively.