| With industrial scale rapid solidification vacuum induction melting furnace, continuous heat treatment furnace and airflow grinding powder equipment, we smelted AB5-type hydrogen storage alloy which cobalt replaced by electro-catalytic alloy C, La replaced by PrNd. Every kind of hydrogen storage alloys were melted per total mass of 400kg. In order to get a good overall electrochemical properties, while reducing the cost of the alloy, based on the commercialization of the AB5 type hydrogen storage alloy, we modified the alloy from the composition, the solidification rate, the heat treatment temperature. We designed a total of nine formulations for industry experimental study, with a view to find the best alloy melting process and heat treatment process and to get the best battery performance and overall electrochemical properties of AB5 type hydrogen storage alloy.In this paper, we changed the composition of the A-side, B-side simultaneously, the PrNd (atomic ratio) content was divided into three levels 0,0.1,0.2 to replace La element, the electro-catalytic alloy C (atomic ratio) content was divided into three levels 0,0.15,0.3 to alternate Co element, making ingredients change on the integrated electrochemical properties of the alloy more comprehensive and detailed. X-ray diffraction analysis and Lattice constant calculation showed that, alloy cell volume increased with the increase of electro-catalytic alloy C, alloy cell volume increased with the increase of PrNd and the decrease of the lanthanum. After high temperature heat treatment, alloy cell volume decreased.Electrochemical tests showed that the alloy without heat treatment, with the increase of C, the maximum discharge capacity decreased from 349.2mAh/g (C=0) to 337.6mAh/g (C=0.3). After 650℃ heat treatment the maximum discharge capacity decreased with the increase of C. After 900℃ heat treatment, the maximum discharge capacity increased with the increase of C, from 324.5mAh/g (C=0) to 332.1mAh/g (C=0.3). Cycling performance deteriorated with increasing Electro-catalytic C content of the alloy.Capacity decay rate of the low-Co-high-La hydrogen storage alloy increased from 1.038mAhg-1cycle-1(C=0) to1.404 mAhg-1 cycle-1 (C=0.3); After 900℃ heat treatment, cycling performance significantly improved, the rate of decay significantly reduced, experiment showed that capacity decay rate was 0.4mAhg-1cycle-1(C=0) and 0.844 mAhg-1cycle-1(C=0.3). Capacity decay rate of the low-Co-high-La hydrogen storage alloy increased larger firstly then smaller with the increase of PrNd. Capacity decay rate increased from 1.038mAhg-1cycle-1 (x=0) to 1.238mAhg-1cycle-1 (x=0.1) and then decreased to 1.15mAhg-1cycle-1(x=0.2). After high temperature heat treatment, cycling performance were improved significantly. After 900℃ heat treatment, Capacity decay rate increased from 0.4mAhg"’cycle"’(x=0) to 0.978mAhg-1cycle-1 (x=0.1) and then decreased to 0.463mAhg-1cycle-1(x=0.2). Alloy high rate performance was poor without alternative alloy, HRD2oo=83.24%, HRD600=70.79%, HRD1000=60.84%; alloy high rate performance was improved with alternative electro-catalytic alloy C, HRD2oo=87.88%, HRD600=73.3%, HRD1000=71.55%.We used cyclic voltammetry curves and tafel polarization plots to study alloy electrochemical kinetics. Before heat treatment, hydrogen diffusion coefficient was 3.22×10-8 cm2S-1 (C=0),3.00×10-8 cm2S-1 (C=0.15),3.09×10-8 cm2s-1 (C=0.3). But after 900℃ heat treatment, with the increase of C, hydrogen diffusion coefficient increased from 1.79×10-8 cm2s-1 (C=0) to 1.95×10-8 cm2s-1(C=0.15) and then increased to 2.65×10-8 cm2s-1(C=0.3), which significantly increased the rate of diffusion of hydrogen atoms in the bulk of the alloy. After 650℃ heat treatment, with the increase of C, hydrogen diffusion coefficient increased from 2.02×10-8 cm2s-1 (C=0) to 3.29×10-8 cm2s-1(C=0.3). Before heat treatment, under the conditions of anodic polarization, oxidation reaction rate was greater than the reduction rate, oxidation and reduction reaction rate increased with the increase of Electro-catalytic C. Under the conditions of cathodic polarization, reduction reaction rate was greater than the oxidation rate, with the increase of C, oxidation and reduction reaction rate firstly decreased and then increased. The addition of Electro-catalytic alloy C improved the catalytic activity and conductivity.The current density increased with the increase of cell volume. Hydrogen diffusion coefficient increased with the increase of cell volume. Under the conditions of anodic polarization, Oxidation-reduction rate of electrode increased with the increase cell volume. Under the conditions of cathodic polarization, oxidation-reduction reaction rate had no correlation between cell volume of the alloy.Through these studies, we determined the condition of the alloy production for two purposes. (1)Suitable for high power nickel-metal hydride batteries.:Electro-catalytic alloy C alternative amount atomic ratio is 0.3, PrNd alternative amount atomic ratio is 0, single roll speed is 300r/min, high-temperature heat treatment helps to improve the stability of Jong-cycle discharge. (2) Suitable for economical production of high-capacity Ni-MH battery technology:Electro-catalytic alloy C alternative amount atomic ratio is 0.15, PrNd alternative amount atomic ratio is 0.2, single roll speed is 300r/min. |
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