An Investigation On The Microstructure And Electrochemical Properties Of The Ti-Ni Based Hydrogen Storage Electrode Alloys

In this thesis, the Ti-Ni based hydrogen storage electrode alloys were selected as the subject on the basis of precious research works on Ti based hydrogen storage alloys which have been extensively reviewed and due to its excellent resistance of corrosion,strong resistance to pulverization, low component number and can be easily used in practical application .In this research,TiNi,Ti₂Ni and Ti₃Ni₂ binary amorphous alloys were prepared by mechanical alloying with Ti and Ni. The microstructure and electrochemical properties of different as-milled Ti-Ni based hydrogen alloys were investigated systemically by means of XRD,RDF,SEM,DSC analysis and the electrochemical test methods, from which the Ti-Ni based alloys milled for 70h with the highest discharge capacity and a better overall electrode properties were selected for further study. Then the effect of annealing treatment on the phase structures and electrochemical properties of Ti-Ni based hydrogen storage alloy's electrodes were investigated in order to improve the overall electrochemical properties of the alloys.The results of the study of XRD analysis indicate that Ti diffuse into Ni ,as a result, alloys formed under mechanical force during the process of mechanical alloying. After milling 10h, part alloys of TiNi,Ti₂Ni and Ti₃Ni₂ were formed,and amorphisation occured for longer milling time, after milling for 70h amorphous were formed with representative broad amorphous peak.Applied XRD data to calculate RDF and g(r) indicated that the samples after milling 70h had long-range ordering and disorder in shorter distance charceteristic.The exothermal curves of TiNi alloys powder with different milling time were measured by DSC.For powder milling 30h, there exists a wide exothermal platue from about 2000C to 4000C which cause by the relaxation of strain energy accumulated during milling. The sharp exothermal peaks appear for the powder milling for 70h and 100h which caused by crystallization of amorphous phase.The stress released completely during crystallization process and formed polycrystal phase structure with mostly TiNi and Ti₂Ni phase.With the ball-milling time postponement the amorphorization degree increased, thus leading to the increment of discharge capacity. The Ti3Ni2 alloy electrode for milling 70h had the maximum discharge capacity (173.3mAh/g) among three kinds of amorphous alloys. Alloy electrodes of TiNi was difficult to be activated ,which discharge capacity increased gradually during the charge-discharge cycles. Alloy electrodes of Ti₂Ni and Ti₃Ni₂ had high initial discharge capacity, but the cycling stability and discharge capacity decreased with the increase of cycle number. The crystallizations of three kinds of amorphous alloys by annealing heattreated improved their discharge capacity,and Ti2Ni alloy electrode had the maximum discharge capacity(289.2mAh/g) among those,but the cyclic capability deteriorated quickly except TiNi alloy eledtrode.The electrochemical performance tests indicated that dynamic performances of alloy electrodes were relatively preferable and the oxidation and deoxidization of hydrogen dominated electrode reaction. Annealing heattreatment and prolong ball-milling time can improve the reactive ability of alloy electrodes and among those electrodes Ti₃Ni₂ alloy electride had the best integrated electrochemical properties.