| In this thesis, previous research works on non-AB5 type RE-based hydrogen storage alloys have been extensively reviewed. On this basis, the La-Mg-Ni-Co based hydrogen storage electrode alloys were selected as the subject of this study. By means of XRD analysis and the electrochemical test methods such as galvanostatic charge-discharge, linear polarization, potentialstatic discharge etc., the phase structure and electrochemical properties of La2Mg(Ni0.85Co0.15)x(x=9.0-10.5) alloys were studied systematically, and from which the AB3.2-type La2Mg(Ni0.85Co0.15)9.6 alloy with a better overall electrode properties was selected for further study. Then the part substitution of Co elements for Ni in AB3 2-type alloy was conducted for examining the effect of Co substitution on the phase structure and electrochemical properties of La2Mg(Ni1-xCox) 9.6 (x=0.1-0.5) alloys. Based on these works, the effect of the amount of substitutions of Co and Al for Ni on the phase structure and electrochemical properties of the La2Mg(Ni0.8-xCo0.2Alx)9.6 (x=0.01-0.03) alloys (AB3.2-type) and La2.2Mg0.8(Ni0.8-xCo0.2Alx)9.6(x=0.01-0.03) alloys (AB3.2-type) were studied in order to improve the overall electrochemical properties of the alloys.For the La2Mg(Ni0.85Co0.15)x(x=9.0-10.5) alloys, the effects of Non-stoichiometry on the phase structure and electrochemical properties were systemically investigated. It is found that the main phase of the alloys and their hydrides preserves the PuNi3 type structure but shows a large unit cell expansion rate on hydriding (â–³F/F=24.9%-23.0%). With increasing of x, the discharge capacity of the alloys decreases from 422mAh/g (x=9.0) to 323.1mAh/g (x=10.5). The high-rate dischargeability (HRD) of the alloy electrodes increases with increasing of x and get a maximum at x=10.5 (HRD800=91.5%). The cycling capacity retention rate of the alloys after 100 cycles (S/oo) reaches 45.2-68.5%, which needs to be further improved.For improving the cycling stability of the alloys, the Ni in La2MgNi9.6 alloy was partly substituted by Co, and the La2Mg(Ni1-xCox)9.6 (x=0.1-0.5) alloys were studied to examine the effect of Co substitution on the phase structure and electrochemical properties of the alloys. It is found that the alloys and their hydrides still preserve the PuNi3 type structure and show a noticeable decrease in unit cell expansion rate (â–³F/F=24.6% as x=0.1; â–³V/V =15.0% as x=0.5)on hydriding. The substitution leads to some decrease in discharge capacity, decreasing from 406.3 mAh/g (x=0.1) to 364.5 mAh/g (x=0.5). The high-rate dischargeability which increases with the increases of x and then decreases, pass throuth a maximum (HRD800=84.8%) at x=0.4. And the cycling stability increases with the increase of x, the cycling capacity retention rate of the alloys after 100 cycles (S100) increased from 64.1 %(x=0.1) to 69.5%(x=0.5).Based on these results, Co and Al were selected as the substitution element for Ni in a AB3.2-tpye alloy and the effect of Co and Al of substittution on the phase structure and electrochemical properties of the La2Mg(Ni0.8-xCo0.2Alx)9.6(x=0.01-0.03) alloys were investigated. It is found that the above alloys still preserve PuNi3 type structure, the increase of Al content leads to an increase in unit cell volume of the alloys but leads to a remarkable decrease in cell volume expansion on hydriding, The discharge capacity of the alloys decrease from 397.2mAh/g(x=0.01) to 370.8mAh/g(x=0.03) while the increase of x in the alloys results in a serious decrease in high-rate dischargeability (HRD400 decreases from 50.5%(x=0.01) to 15.1%(x=0.03) but an improvement in cycling stability (S100 increases from 57.6% for x=0.01 to 59.7% for x=0.03). It is found that the serious decrease of HRD of the alloys is mainly due to the decrease in both of electrocatalytic activity andthe hydrogen diffusion rate in the alloy bulk.To further improve the overall properties of the alloys, the effect of La/Mg rate and the Al substitution for Ni in the alloy on the phase structure and electrochemical properties of the La2. |
