| As the most common negative electrode material for MH/Ni batteries,capacity,cycle and dynamic performance of AB5-type rare earth-based hydrogen storage alloys have been a hot spot to research for years.In the purpose of improving capacity,this paper mainly studies the performance of 80VFe/AB5 type rare earth based hydrogen storage composite alloys(i.e.matrix alloy)by a vacuum arc melting method.And XRD,SEM and electrochemical testing are also used to characterize the properties of the hydrogen storage alloys.After the cycling tests at 0.2C,1C,3C and 5C,it is clear that the maximum capacity of 3#alloys electrode(compositing with 3%80VFe)reaches 326.8 mAh/g at 0.2C,higher than that of matrix alloy 1#(without 80VFe)by 7.8 mAh/g.When discharge to 0 V at 0.2C,the maximum capacity of 3#alloys electrode reaches 402.7 mAh/g,higher than that of matrix alloy 1#by 22.6 mAh/g.With the increasing of discharge ratio,the improving degree of 80VFe's content to the capacity of the alloy battery gradually decreases.Study on the different rates of the battery capacity fading rate show that when composite with 3%80VFe,the cycle stability of the material is better,from 0.92 mAh/(g·cycle)at 0.2C increases to 1.18 mAh/(g·cycle)at 5C,while without 80VFe,the value varies from 4.2%to 5.6%.Therefore,AB5 hydrogen storage alloys combined with a certain amount of 80VFe can improve the capacity and cycling stability of the alloys electrode,but it is not very obvious for high rate discharge performance.The comparision of the SEM and XRD images of the alloy particles before and after the cycle indicates that before cycle,the main phase of the alloy is LaNi5,and the second phase appears with the increase of 80VFe.And the diffraction peak intensity of the alloy particles without cycling is larger and the shape of the peak of that is sharper.SEM results show that when the content of 80VFe increases from 3%,the segregation phase in the alloy increases obviously,thus reducing the capacity of the battery.And the SEM test indicates that the particles of the alloy are obviously smaller and a large number of cracks appeare on the surface after cyclic.However,after cycling,the intensity of the diffraction peak of the alloy particle is significantly weakened and broadened.The analysis of the chemical composition before and after the cycle of the alloy particles shows that the contents of La,V and Cu in the particles decrease uniformly at different discharge rates,while the content of oxygen increases uniformly.This is also one of the main reasons for the reducing the capacity of the alloy battery.Polarization resistance,as one of the kinetic parameters of alloys electrodes,is measured by linear polarization method.The results show that with the increase of 80VFe,the polarization resistance of the alloys electrode decreases first and then increases,and the exchange current first increases and then decreases.When the 80VFe content is 3%,the resistance is the lowest,valued 267.79 m?·g,and the corresponding exchange current is the highest 97.51 mA/g.The charge resistance and the exchange current measured by the AC impedance method are the same as those obtained by linear polarization method.The analysis of cyclic voltammetry and constant current intermittent titration curves shows that the hydrogen diffusion coefficient of the alloy with 3%80VFe is the biggest. |
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