Capacity degradation of Laves phase-related body-centered-cubic solid solution metal hydride alloys in battery

Abstract The nickel/metal hydride (Ni/MH) is a good example of using metal hydride alloy which is cable of reversely storing the hydrogen energy in an electrochemical environment. The failure mode of two Laves phase-related body-centered-cubic metal hydride alloys doped with Y, and Ce separately in sealed Ni/MH batteries is studied by scanning electron microscopy with x-ray energy dispersive spectroscopy and x-ray diffraction analysis. These two alloys come from a series of studies targeting toward using Ni/MH battery as a low-cost and high-durability alternative to rival Li-ion battery in the electric vehicle application. This group of alloys demonstrates a discharge capacity up to 400 mAh g −1 under a C/4 discharge rate. The main failure mode of these two alloys is found to be selective dissolution of C14 phase which contributes to a fast increase in internal resistance. Due to the deprival of Cr from the first solidified BCC phase, the next solidified C14 phase does not have enough Cr to protect it from the KOH corrosion. Rapid quench fabrication method and addition of other corrosion-resistant non-BCC former, such as Cu, Pd, and Hf, in the alloy composition are suggested.