Influence Of Microstructure And Electrochemical Properties Of La-Gd-Y-Ni System A₅B₁₉ Type Hydrogen Storage Alloy

As a new generation of nickel-hydrogen battery negative electrode materials,La-Y-NiAB_3-4 superstructure hydrogen storage alloys have greater advantages in discharge capacity and rate discharge compared to traditional AB₅ hydrogen storage alloys.However,the complex stacking structure of the superstructure hydrogen storage alloy also brings about the problem of insufficient cycle stability.Therefore,how to improve the electrochemical cycling life of the superstructure hydrogen storage alloy has become a key issue for its application in high-capacity nickel-hydrogen batteries.Element substitution is considered to be the most economically effective method to improve the performance of hydrogen storage alloys.Previous studies have shown that partial substitution of Gd element in La-Mg-NiA₂B₇ hydrogen storage alloy can significantly improve the electrochemical performance of the alloy,especially in terms of cycle stability.A₅B₁₉ hydrogen storage alloy has more[AB₅]stacking structure units than A₂B₇ hydrogen storage alloy,thus its theoretical structure stability is better.However,so far,there have been no reports on the effect of Gd substitution on the hydrogen storage performance of magnesium-free La-Y-NiA₅B₁₉ hydrogen storage alloy,especially the mechanism of the effect of Gd substitution on the cycle stability of the alloy is not clear.In this paper,hydrogen storage alloys of annealed ANi_3.33Mn_0.17Co_0.2Al_0.1（A=La,Gd,Y）,La_xY_yGd_1-x-yNi_3.33Mn_0.17Co_0.2Al_0.1（0.2≤x≤0.4,0≤y≤0.8）,and La_0.3Gd_0.5Y_0.2Ni_3.43-xCo_0.2Mn_0.17Al_x（x=0.1,0.2,0.3）were prepared to investigate.the effects of the microstructure,hydrogen storage properties and electrochemical properties of the La-Gd-Y-Nisystem A₅B₁₉ type hydrogen storage alloys were investigated.The research results are as follows:（1）Based on ANi_3.33Mn_0.17Co_0.2Al_0.1（A=La,Gd,Y）hydrogen storage alloys,it was found that the cell volume and cell parameters of the alloy increased with the increase of the atomic size of A-side elements.Among them,the Gd alloy showed excellent inherent corrosion resistance,and its capacity almost did not decay during the cycling process,with a cycling stability of S₁₀₀=98.8%.Gas-phase hydrogen storage tests showed that the maximum discharge capacity of the Gd alloy was only 266.3 m Ah/g due to the influence of the high hydrogen absorption and release plateau.（2）The previous work of the research group showed that Lawith a large atomic size can significantly reduce the hydrogen absorption and release plateau pressure of the hydrogen storage alloy,and Y with a light molar mass can effectively improve the specific capacity of the alloy.By synergistic effects of La,Y,and Gd on the A-side,La_xY_yGd_1-x-yNi_3.33Mn_0.17Co_0.2Al_0.1（0.2≤x≤0.4,0≤y≤0.8）hydrogen storage alloys were prepared.The study found that Lasubstitution for Gd was beneficial to improve the mass fraction of the A₅B₁₉ phase in the alloy,while Y substitution for Gd reduced the mass fraction of the A₅B₁₉ phase in the alloy.At the same time,the cell parameters and subunit volumes of all phases in the alloy increased with the increase of A-side atomic size,Lasubstitution exacerbated the occurrence of powdering and hydrogen-induced amorphization in the alloy,while Y substitution slowed down the hydrogen-induced amorphization tendency in the alloy.Laand Y partially substituting for Gd significantly improved the comprehensive electrochemical performance of the alloy.Lawith a large atomic size significantly reduced the electrode hydrogen absorption and release plateau pressure,thereby improving the electrochemical capacity of the alloy.Y,as a light rare earth element with a low molar mass,significantly improved the specific capacity of the alloy.However,as the substitution amount of Laand Y increased,the cycling stability of the alloy electrode decreased.Among them,La_0.3Gd_0.5Y_0.2Ni_3.33Mn_0.17Co_0.2Al_0.1 showed the best comprehensive electrochemical performance:C_max=354.2 m Ah/g,S₁₀₀=91.8%,HRD₉₀₀=80.6%.（3）In order to further reduce the hydrogen absorption and desorption plateau pressure of the alloy and improve its cycle stability,La_0.3Gd_0.5Y_0.2Ni_3.43-xCo_0.2Mn_0.17Al_x（x=0.1,0.2,0.3）hydrogen storage alloys were prepared by partially substituting Al for Ni.It was found that with the increase of Al content in the alloy,the AB₅ type phase appeared in the alloy phase,and the change in phase composition deteriorated the comprehensive electrochemical performance of the alloy.The maximum discharge capacity of the alloy decreased from 354.2 m Ah/g for the x=0alloy to 325.2 m Ah/g for the x=0.3 alloy.Meanwhile,affected by the alloy pulverization and intrinsic corrosion resistance,the cycle stability of the alloy increased first and then decreased with the increase of Al content.