Structure And Electrochemical Properties Of La-RE-Mg-Ni-Al?RE=Nd,Sm? AB₄-type Hydrogen Storage Alloy Negative Electrode Materials

La-RE-Mg-Ni-Al-base hydrogen storage alloy was prepared by induction melting,and a novel AB₄-phase structural alloy was produced by annealing at different temperatures.The phase structure transformation mechanism of AB4-phase alloy was studied,and the electrochemical properties of different alloy electrode samples were tested.The effects of annealing treatment on the phase structure and the electrochemical and kinetic properties of the alloy and the electrochemical properties of AB₄ relative to Pr₅Co₁₉phase alloy were studied.The results show that La Ni₅,MgCu₄Sn and Ce₅Co₁₉ three phase structures are contained in the as-cast La-Sm-Nd-Mg-Ni-Al-base alloy.After 12 hours heat treatment at900?,MgCu₄Sn phase disappeared,LaNi₅ phase decreased,and a new phase Ce₂Ni₇phase was produced.The new phase Ce₂Ni₇ will continue to produce an peritectic reaction with the remaining unreacted LaNi₅ phase,which will be converted to Ce₅Co₁₉ phase,and the content of Ce₅Co₁₉ phase will increase.When the annealing temperature rose to 960?,the two phases of Ce₂Ni₇ and La Ni₅ completely disappeared,and Pr₅Co₁₉ phase appeared.The maximum discharge capacity was 369.8 mAh g^-1.Pr₅Co₁₉ phase monophase alloy was formed under annealing at 970?.Pr₅Co₁₉ phase disappeared in AB₄ phase under annealing condition of 975?,the capacity holding rate of 200 weeks was 83.2%,the discharge capacity could reach 138.5 mAh g^-11 at-40?,and the high rate performance was improved from 24.93%?as-cast alloy?to 34.06%.Its exchange current density I₀,limit current density and hydrogen diffusion coefficient are all higher than those of other heat treated alloys,indicating that the appearance of AB₄ phase is beneficial to the high ratio performance of the alloy.Pr₅Co₁₉ single-phase alloy and two-phase La-Sm-Mg-Ni-Al alloy containing AB₄ and Pr5Co19 were prepared,and their electrochemical properties and hydrogen storage properties were studied.The results show that with the increase of the AB₄ phase content,the microstructure of the Pr₅Co₁₉ phase is not changed,and the maximum discharge capacity of the alloy is improved,showing good high rate performance and hydrogen absorption and desorption performance.And through the comparative study of its hydrogen storage performance,it was found that increasing the content of AB₄ phase makes the enthalpy of formation of hydride increase,the enthalpy of dehydrogenation decreases,improves the thermodynamic properties of the alloy,the stability of hydride decreases,and the hydrogen atom diffusion at current density is easier,thus exhibiting better high-rate discharge performance.