Preparation And Electrochemical Properties Of Mg-based Hydrogen Storage Alloys

Mg-based hydrogen storage alloy has been paid great attention because of its high theoretical capacity, low cost and abundant resource. But it is inadequate for practical use for MH/Ni battery because of its poor cycle life in KOH solution. To overcome these shortcomings, many efforts have been made to improve its electrochemical characteristics, such as element substitution ,surface modifications and elaboration of alloy composites.MgNi and Mg-Ti-Ni were successfully synthesized by mechanical alloying(MA). and the effects of the ball-milling time, element substitutions (Mg_1-xTi_xNi(x=0.1,0.2)) on the electrochemical properties of MgNi alloy were deeply studied. It was found that the cycle lives of the alloys were improved with Ti partial substitution, while at the sacrifice of the discharge capacity: the discharge capacity of the Mg_0.8Ti_0.2Ni alloy electrode was 218.34 mAh·g^-1, and the capacity maintenance rate was 66.87% after 20 cycles, the first discharge capacities of the Mg_0.9Ti_0.1 Al_0.1Ni_0.995Zn_0.005 alloy was 178.6mAh/g , and the capacity maintaining rate was 56% after 16 cycles.The structure and the electrochemical characteristics of the composit with TiNi alloys were studied. The results of X-ray diffraction and scanning electron microscope show that the alloys have amorphous structures. The charge-discharge cycle tests indicate that the cycle performance of these alloys are better than those of MgNi alloys, although the first discharge capacities are a litter lower than that of the MgNi alloys. Take the MgNi-10% TiNi_0.5Mn_0.5 for example , the first discharge capacities is 394.46 mAh/g , and the capacity maintaining rate is 58.96% after 50 cycles. Potentiodynamic polarization curves prove that anti-corrosion performance of the electrodes become better; Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests show that the introduction of the TiNi alloys decrease the charge-transfer reaction resistance and the H atom diffusion impedance and the electrode catalytic activity improve significantly.According to the specific information on the discharging capacity and cycling stability of the MgNi-TiNi_0.56M_0.44(M=Al,Fe) alloys , MgNi-x%TiNi_0.5Mn_0.5(x=10,30,50),MgNi-TiNi_0.44Co_0.56 alloys, It is noticed that with 10% TiNi_0.44Co_0.56 and grinding for 10h are proper condition to MgNi alloy. Because the capacity is highest and the capacity maintaining rate are higher than othersThe results of the composed with amorphous CoB powder and modified by mechanical grinding in tetrahydrofuran (THF) showed that: The cycle life of the electrode was improved by CoB, the composite particles seem to be smaller and larger interfaces, from which the electrode performance will benefit. The capacity maintaining rate is 46.69% after 20 cycles. The discharge capacity of MgNi alloy modified with THF decreased; the cycle performance became better, but the specific information on electrochemical characteristics was not well.