Regeneration of the Ni-H Cathode Active Material in Rechargeable Battery by Calciothermic Reduction Flexing Process

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The investigators have proposed an efficient process to regenerate the Ni-H cathode active material in the spent rechargeable battery by using calciothermic reduction and fluxing methods. to develop the proposed process, the reaction mechanism and the effect of process factors in the calciothermic reduction method to directly synthesize the Ni-RE(rare earth) hydrogen storage alloy from the rave earth oxide (RE_2O_3) in the spent battery with calcium as a reductant were investigated in the present study. Solubility of RE_2O_3 and CaO or MgO in the B_2O_3 base flux was also investigated to look for the optimum condition in the fluxing method to synthesized Ni-RE alloy from the residual RE_2O_3 and CaO or MgO.It was found that calciothermic reduction and the resultant formation of Ni-RE alloy were completed in a very short time of 30min with 1.5 equivalents of Ca at 900℃. The PCT measurement has clarified that the synthesized alloy particles have the hydrogen-absorbing properties which are nearly same as those of commercial Ni-RE hydrogen storage alloys. The contents of calcium and oxygen in the synthesized alloy could be decreased from 0.5 and 1.2 wt% to 0.1 and 0.3wt%, respectively, by melting for 4 hrs at 1350℃.Phase diagrams for the B_2O_3-CaO-RE_2O_3(RE: La and Nd) and B_2O_3-MgO-RE_2O_3 systems were experimentally determined at 1350℃ It was clarified that the solid phase equilibrating with the liquid phase is a RE_2O_3-B_2O_3 compound with a mole ratio of 1/1 without CaO or MgO. Both of the MgO-B_2O_3 and CaP-B_2O_3 base fluxes were found to be amenable for efficiently fluxing the rare earth oxides.