Study On The Preparation,Composition And Electrochemistry Property Of LaMg₂Ni_9-x-y-zCo_xMn_yCu_z Series Hydrogen Storage Alloys

In this article LaMg₂Ni_9-x-y-zCo_xMn_yCu_z(x=1.8,2.1,2.4,2.7,3.0,y=2.1,2.4, 2.7,3.0,3.3,z=0.3,0.6,0.9,1.2,1.5)series hydrogen storage alloys were prepared by coprecipitation-reduction-diffusion method according to the orthogonal Experimental.The preparation conditions,components,electrochemistry characteristics and phases of the alloys were studied in order to enhance its synthetic electrochemistry performance by diversified the alloys' composition.Research indicate that the alloys have uniform granularity with little Ca when they were prepared in the water-bath of 70℃,stirring speed of 400rad/min,dropping precipitant speed of 5ml/min,washing the alloys by deionized water and acetic acid alternately.The compositions of the alloys were studied by chemical analyses as well as the theoretical deduction,the result show that the chemical composition of LaMg₂Ni_9-x-y-zCo_xMn_yCu_z series hydrogen storage alloys is close to the metallic ion amount added at beginning of the preparation.The maximum discharge capacity of this series alloys is higher than the alloys substituted by single element,the average value is 184.88mAh/g,and the maximum discharge capacity of LaMg₂Ni_2.7Co_2.1Mn_2.7Cu_1.5is the highest,which is 365mAh/g.The discharge capacity decline rate after 100 cycles of this series alloys is higher than the alloys substituted by single element,the average value is 49.64%and the cycle stability of LaMg₂Ni_1.2Co_3.0Mn_3.3Cu_1.5is the best,with the discharge capacity decline rate of 29.38%.The changes of alloys' composition have little influence on activation process,the activation process needs only 1～5 cycles,that is better than alloys substituted by single element.According to the study,the synthetic electrochemistry performance of LaMg₂Ni_2.7Co_2.1Mn_2.7Cu_1.5is the best,its maximum discharge capacity is 365mAh/g,discharge capacity decline rate after 100 cycles is 36.38%,and activation process is 2 cycles.The XRD results indicate that the phase structure of this series alloys is more diversified,the main phase of LaMg₂Ni_2.7Co_2.1Mn_2.7Cu_1.5is La₄Co₃,which has the best synthetic electrochemistry performance.The main phase of LaMg₂Ni_1.2Co_3.0Mn_3.3Cu_1.5is LaNi₅ and some La₄Co₃, which has the best the cycle stability.The main phase of both LaMg₂Ni_4.8Co_1.8Mn_2.1Cu_0.3and LaMg₂Ni_3.9Co_2.1Mn_2.1Cu_0.9is Co,which has the lowest maximum discharge capacity and the worst cycle stability,respectively.The preliminary conclusion is that La₄Co₃ phase can enhances the synthetic electrochemistry performance of this series alloys,LaNi₅ phase can enhances the cycle stability and Co phase can make the synthetic electrochemistry performance worse.