Flame Sprayed LaNi₅-Based Mischmetal Alloy: Building-up Negative Electrodes for Potential Application in Ni-Based Batteries

AB₅-type metal hydrides have received important attention over the last few decades because of their capacity to reversibly absorb hydrogen. The AB₅-type alloys have been widely used as negative electrodes in Nickel metal hydride (Ni-MH) batteries, replacing the toxic counterparts that are present in Ni-Cd systems. Until now, fabrication of this type of electrode is often carried out by dry compaction, wet paste, and dry paste methods. In the present study, the oxyacetylene combustion flame spray process is explored as an alternative method for the production of LaNi₅-based Mischmetal electrodes. A factorial experimental design has been proposed to optimize processing conditions in order to obtain negative electrodes for Ni-MH cells. The results of this work have shown that negative electrodes can be successfully fabricated by flame spray and that the thermal spraying processing conditions employed resulted in different levels of porosity and thickness. LaNi₅-based porous coatings were selected after thermal spray optimization and their electrochemical performance was evaluated in a 6M KOH electrolyte. The results also revealed that the change in the chemical composition of the electrodes during thermal spraying significantly affects the electrochemical performance by reducing 49% the hydrogen storage capacity with respect to that of the feedstock material.