The progress of nanocrystalline hydride electrode materials

摘要

This paper reviews research at the Institute of Materials Science and Engineering,Poznari University of Technology,on the synthesis of nanocrystalline hydride electrode materials.Nanocrystalline materials have been synthesized by mechanical alloying(MA)followed by annealing Examples of the materials include TiFe-,ZrV?-,LaNi§ and Mg2Ni-type phases.Details on the process used and the enhancement of properties due to the nanoscale structures are presented.The synthesized alloys were used as negative electrode materials for Ni-MH battery.The properties of hydrogen host materials can be modified substantially by alloying to obtain the desired storage characteristics.For example,it was found that the respective replacement of Fe in TiFe by Ni and/or by Cr,Co.Mo improved not only the discharge capacity but also the cycle life of these electrodes.The hydrogen storage properties of nanocrystalline ZrV2- and LaNi_5-type powders prepared by mechanical alloying and annealing show no big difference with those of melt casting(polycrystalline)alloys.On the other hand,a partial substitution of Mg by Mn or Al in Mg_2Ni alloy leads to an increase in discharge capacity,at room temperature.Furthermore,the effect of the nickel and graphite coating on the structure of some nanocrystalline alloys and the electrodes characteristics were investigated.In the case of Mg2Ni-type alloy mechanical coating with graphite effectively reduced the degradation rate of the studied electrode materials.The combination of a nanocrystalline TiFe-.2- and LaNi5-type hydride electrodes and a nickel positive electrode to form a Ni-MH battery,has been successful.