| The AB5-type rare-earth based hydrogen storage alloy is applied to MH/Ni secondary batteries.And it is the most mature and commercialize.However,cycle life is a key factor that decides the practical value of the hydrogen storage alloy,and the poor power performance and relatively high cost limit the use of AB5 type hydrogen storage alloy batteries as power sources.In view of the above problems,in this paper,I mainly study the reasons of capacity decay in hydrogen storage alloy,and the corresponding solutions,A-side,B-side composition optimization to explore the crystal structure and electrochemical properties of hydrogen storage alloys.The contents of PrNdCe elements replace the La respectively,designed B-side element Co with the atomic ratio respectively.First,Among the A-side Components varied samples,the electrochemical tests showed that the discharge maximum capacity was decreased with PrNdCe elements increase at 1C to 4C.When the discharge ratios up to 5C,the maximum capacity was improved with PrNdCe elements raise.With the increasing of discharge rates,The minimum increasing of capacity decay rate was the sample with high PrNdCe content,from the value 0.23mAh/g cycle at 1C to 0.68mAh/g·cycle at 5C.It explained that with the increasing of PrNdCe elements in hydrogen storage alloys,the high-current discharge ability and cyclic stability could be improved.Applied linear polarization method to study the kinetic parameters of the samples,which got the result that the polarization resistances Rp was increased from 388.65m?·g to 487.15m?·g.Corresponding exchange currents I0 were decreased from 69.72mAh/g to 52.34mAh/g with PrNdCe content increasing.The hydrogen diffusion coefficient D was decreased with Co content increasing by Cyclic Voltammetry by GITT.The oxidation reaction rate and the reduction reaction rate of the alloy electrode were reduces with the PrNdCe content enhance.Second,Among the A-side Components varied samples,the electrochemical tests showed that with Co content increase the cycle stability and high current discharge capacity was improved.With Co content decrease.Applied linear polarization method to study the kinetic parameters of the samples,which got the result that the polarization resistances Rp was decreased from 392.42m?·g to 275.65m?·g.Corresponding exchange currents I0 were increased from 70.25mAh/g to 96.64mAh/g with Co content decreasing.The hydrogen diffusion coefficient D was increased with Co content decreasing by Cyclic Voltammetry by GITT.The oxidation reaction rate and the reduction reaction rate of the alloy electrode were increased with the Co content to reducing.At last,The reason of the capacity decay in the cycle of the hydrogen storage alloy cell was studied.Analyzed the X-ray diffraction and SEM graphs alloy powders with 40,80 charge-discharge cycles at 0.2C.The diffraction peak intensity of alloy powders with charge-discharge cycles decreased obviously,and along with a peak width phenomenon,which revealed that the crystalline grains distort and the integrity of the lattice was destroyed.Meantime,the alloy powder surface appeared a large number of cracks,and had many fine alloy powders.Furthermore,the alloy surface appeared loose.The alloys were subjected to 40 cycles of 1C,3C,5C charge and discharge cycles respectively.Analyzed the X-ray diffraction and SEM graphs show that the diffraction peak intensities were decreased with the increase of the discharge rate.T he peak width increase shows that the high rate of discharge accelerated lattice distortion and the destruction of lattice integrity.The rate of discharge increased the particle size of the alloy and the more obvious the degree of powdering.After the chemical composition of the alloy cycle,the higher the charge and discharge rate of the battery powder,the alloy of La,Co,Mn loss rate is higher.With the increase of PrNdCe content,the loss rate of La and Co increases,while the loss rate of Mn decreases. |
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