Investigation On The Electrochemical Properties Of La-Mg-Ni-based A₂B₇-type Hydrogen Storage Electrode Alloys

Recently, the high electrochemical capacity La-Mg-Ni-based A₂B₇-type hydrogen storageelectrode alloy which have attracted increasing attention have been researched in this paper. Aiming atproposing the electrochemical performances of La-Mg-Ni-based A₂B₇-type La0.75Mg0.25Ni3.5hydrogenstorage electrode alloy. The effect of multi-alloying on the microstructure and electrochemicalproperties of La0.75Mg0.25Ni3.5-xMox（x=0⁰.5） hydrogen storage alloy electrode were systematicallystudied by means of XRD, OM, SEM, TEM, electrochemical workstation and electrochemicalmeasurement system in this thesis. The La_0.75Mg_0.25Ni_3.2Mo_0.3hydrogen storage electrode alloy whichhas excellent electrochemical performances was preferred as the further object, and then theinfluences and mechanisms of melt-quenching preparation method and annealing treatmentpost-processing technology on the microstructure and electrochemical properties of theLa_0.75Mg_0.25Ni_3.2Mo_0.3hydrogen storage electrode alloys were systematically investigated.Using multi-alloying method, Mo was successfully brought into La0.75Mg0.25Ni3.5-xMox（x=0⁰.5）hydrogen storage electrode alloys. It effectively improves the electrochemical reaction rate, thedischarge voltage characteristics and the high rate discharge performance of the electrode alloys. Thepartial substitution of Mo for Ni promotes the formation of the high catalytic activity MoNi₄phaseand the increase of the content of LaNi₅phase which both for hydrogen absorbing phase and catalyticphase. With the increase of Mo content, the high rate discharge performance HRD900of alloys risesfrom82.58%（x=0） to86.72%（x=0.5） and the growth rate is5.1%; When the Mo content is0.3at.%,the alloy shows the better comprehensive electrochemical performances: N=4, Cmax=378.66mAh/g,HRD900=84.75%, S100=76.68%.By changing the quenching speed V to control the internal phase structure and distribution ofalloys, the La_0.75Mg_0.25Ni_3.2Mo_0.3hydrogen storage electrode alloy which with homogeneouscomponents, purity and small-size grains was successfully prepared by melt-quenching preparationtechnology. With the increase of quenching speed V, the content of LaNi₅phase which with goodcycle stability performance increased, and the cycle stability performance of the electrode alloyimproved obviously,100times cycle capacitance keeping-rate S100is up from76.61%（V=0m/s） to83.2%（V=30m/s） and the growth is8.6%.Isothermal atmosphere annealing treatment could effectively improves the component oforganization homogenization of the La_0.75Mg_0.25Ni_3.2Mo_0.3hydrogen storage electrode alloy. Meanwhile, it increases the cell volume and hydrogen storage volume, and improves the dischargecapacity of the electrode alloy. When the annealing temperature T reaches1123K, the electrode alloyhas good phase structure organization uniformity, and shows the most excellent comprehensiveelectrochemical performances: N=4cycles, Cmax=386.86mAh/g, HRD900=86.68%, S100=79.98%. Atthe same time, the maximum discharge capacity of the electrode alloy is increased by2.9%comparedto the matrix alloy.