Abstract
The grain boundaries of three Laves phase-related body-center-cubic (bcc) solid-solution, metal hydride (MH) alloys with different phase abundances were closely examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and more importantly, electron backscatter diffraction (EBSD) techniques. By using EBSD, we were able to identify the alignment of the crystallographic orientations of the three major phases in the alloys (C14, bcc, and B2 structures). This finding confirms the presence of crystallographically sharp interfaces between neighboring phases, which is a basic assumption for synergetic effects in a multi-phase MH system.
Highlights
Metal hydride (MH) alloys are often used as the negative electrode active material in nickel/metal hydride (Ni/MH) batteries, which are currently dominating the hybrid electric vehicle application
We present results achieved by using electron backscatter diffraction (EBSD) to determine the crystallographic orientation relationship among bcc, C14, and B2 phases in Laves phase–related bcc solid solution alloys
The backscattered electron (BSE) image of Alloy P1 shows only one predominant phase (Figure 4a), and the energy dispersive spectroscopy (EDS) mapping shows that the elemental distribution is uniform in most regions, except occasional V and Zr inclusions (Figure 4b)
Summary
Metal hydride (MH) alloys are often used as the negative electrode active material in nickel/metal hydride (Ni/MH) batteries, which are currently dominating the hybrid electric vehicle application.To compete with Li-ion batteries in the battery-powered electric vehicles, the gravimetric energy density of Ni/MH batteries needs to be enhanced. Through an Advanced Research Projects Agency-Energy sponsored robust affordable generation electric vehicles (RANGE) storage-BASF program, the capacities of both the positive and negative electrode active materials were improved [1]. The former was accomplished by using core-shell-structured β-/α-Ni(OH) , and the latter was developed from a. The bcc phase can store a large amount of hydrogen [3,4], while the Laves phase acts as both a catalytic agent for electrochemical reactions [5,6] and a hydride activation facilitator due to its brittleness [7,8,9] In these alloys, at some compositions and annealing conditions, TiNi-, Ti2 Ni-, and VNi-based secondary phases can be observed [10]. Combining the high-capacity bcc storage phase with catalytic phases (C14, TiNi, Ti2 Ni, and/or VNi), the electrochemical performance of Batteries 2016, 2, 22; doi:10.3390/batteries2030022 www.mdpi.com/journal/batteries
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