Microstructure Characteristics And Electrochemical Properties Of As-Cast And As-Rapidly Quenched Alloys Mg_2-xCa_xNi?X=0⁰.30?

As fossil fuels become increasingly tight,the development and use of clean energy is essential.This brings broad prospects for the application of hydrogen storage alloys.Among the many application fields of hydrogen storage alloys,the application as the anode material of MH-Ni batteries is the most economical.With the development of the times,people's requirements for the performance of MH-Ni batteries are becoming more and more stringent,and it is urgent to develop anode materials for MH-Ni batteries with excellent comprehensive properties.Mg-based hydrogen storage alloys have attracted much attention due to their advantages such as high theoretical capacity,light weight,and abundant reserves.However,due to its low room temperature capacity,poor cycle life and other shortcomings,it still cannot meet the practical application.The electrochemical performance of hydrogen storage alloy is closely related to the abundance of the main hydrogen absorbing phase,microstructure and chemical composition.Therefore,the element replacement and melt-spinning treatments are used to improve the electrochemical performance of Mg₂Ni alloys,and the as-cast and melt-spinning Mg_2-xCa_xNi?x=0?0.30?alloys the microstructure characteristics and electrochemical performance were systematically studied,and some important conclusions were obtained.The microstructure characteristics and electrochemical properties of as-cast Mg_2-xCa_xNi?x=0?0.30?alloys have been found.After the replacement of Mg by Ca,the alloy has a multi-phase structure and consists of the Mg₂Ni phase,Mg Ni₂ phase and Mg₂Ca phase composition,with the increase of Ca content,the content of Mg₂Ca phase gradually increases,but the main phase is still Mg₂Ni phase.Electrochemical tests showed that the maximum discharge capacity of Mg₂Ni alloy was the highest at room temperature,which was 23.92 m Ah/g,and the capacity retention S₅₀=32.9%after 50 cycles.Because the substitution of Ca will form the Mg₂Ca phase in the alloy,the maximum discharge capacity of the as-cast alloy is reduced to varying degrees,but the cycle stability is improved to a certain extent.The as-cast Mg_2-xCa_xNi?x=0?0.30?alloy was quenched at a melt-spinning speed of 10m/s,30 m/s and 50 m/s.The phase composition of the alloy after melt-spinning is the same as that of the as-cast alloy,and no new phase is generated.With the increase of the melt-spinning speed,the grains of the alloy gradually decrease from dendritic crystals to fine cellular crystals,eventually the grain boundaries disappear,the structure becomes continuous,and the composition of the alloy gradually becomes uniform.The cell volume of the Mg₂Ni phase also became smaller.In addition,the melt-spinning speed and the amount of Ca substitution determine the microstructure and electrochemical performance of the alloy.With the increase of the melt-spinning speed and the replacement amount of Ca,the diffraction peaks of the alloy broadened significantly and some of the diffraction peaks disappeared.The increase of Ca substitution amount will promote the formation of amorphous phase.Electrochemical tests show that the overall electrochemical performance of Mg_1.80Ca_0.20Ni alloy is the best at room temperature.When the melt-spinning speed is10 m/s,the maximum discharge capacity of 37.24 m Ah/g is obtained after one cycle and after 50 charge cycles The capacity retention after discharge cycle S₅₀=40.0%,both higher than Mg₂Ni as-cast alloy.In order to solve the problem of low electrochemical capacity of as-cast and rapidly quenched Mg_2-xCa_xNi?x=0?0.30?alloys at room temperature,the electrochemical test temperature was increased to 353 K and it was found that the test temperature can greatly increase the discharge capacity of the alloy,and at the same time make the discharge platform wider and flatter,but the cycle stability of the alloy is extremely poor,and it quickly decays after the first cycle.In summary,the melt-spinning alloys with a melt-spinning speed of 10 m/s all have a large discharge capacity.The maximum discharge capacity and the best discharge characteristics of as-cast and melt-spinning alloys appear from Mg₂Ni alloys.The maximum discharge capacity of the as-cast Mg₂Ni alloy was increased from 23.92 m Ah/g at room temperature to 243 m Ah/g,an increase of 10.2 times.At the melt-spinning speed of 50 m/s,the maximum discharge capacity of Mg₂Ni alloy was from 19.56 m Ah/g at room temperature increased to 348.6 m Ah/g,an increase of 17.8times.