The negative electrode development for a Ni–MH battery prototype

The negative electrode development for a nickel-metal hydride battery (Ni–MH) prototype was performed with the following procedure: (1) the Lm_0.95Ni_3.8Co_0.3Mn_0.3Al_0.4 (Lm=lanthanum rich mischmetal) intermetallic alloy was elaborated by melting the pure elements in an induction furnace inside a boron nitride crucible under an inert atmosphere, (2) the obtained alloy was crushed and sieved between 44 and 74 μm and mixed with teflonized carbon; (3) the compound was assembled together with a current collector and pressed in a cylindrical matrix. The obtained electrode presented a disc shape, with 11 mm diameter and approximately 1 mm thickness. The crystalline structure of the hydrogen storage alloy was examined using X-ray diffractometry. The measured hcp lattice volume was 1.78% larger than the precursor LaNi₅ intermetallic alloy, increasing the available space for hydrogen movement. Energy dispersive spectroscopy (EDS) and scanning electronic microscopy (SEM) measurements were used before and after hydriding in order to verify the alloy sample homogeneity. The negative electrode was electrochemically tested by using a laboratory cell. It activates almost totally in its first cycle, which is an excellent characteristic from the commercial point of view. The maximum discharge capacity reached was 314.2 mA h/g in the 10th cycle.