Electrochemical properties of hypo-stoichiometric Y-doped AB 2 metal hydride alloys at ultra-low temperature

C14 Laves Phase Metal Hydride Alloys for Ni/MH Batteries Applications

“…A TiNi phase was found to increase the discharge capacity, and to improve the charge retention and cycle life while lowering HRD capability [56]. In addition, it is known to improve lowtemperature kinetics [112,113]. The electrochemical performances of TiNi-based MH alloys were previously reported [114][115][116][117].…”

“…In general, the ionic radius, ease of oxidation, and MH-bond strength become smaller when the atomic number increases. Previous studies in a comparison series of RE-doped C14 MH alloys [112,113,[138][139][140][141] showed that the RE-Ni phase is beneficial for activation, but detrimental to HRD and low-temperature performance, and that a careful stoichiometric design is needed to balance the abundance of the RE-Ni and TiNi phases [113]. The incorporation of La provides the greatest low-temperature performance, but a contradictory microstructure (an increase in the detrimental LaNi phase and corresponding decrease in the beneficial TiNi phase).…”

“…Like RE-Ni, the ScNi secondary phase increased discharge capacity, but weakened cycle stability [142]. A combination of hypo-stoichiometry and the addition of RE can boost low-temperature alloy performance [113]. High Mg-content secondary phases have been detected and facilitate the activation process [143,144].…”

Studies on Incorporation of Mg in Zr-Based AB2 Metal Hydride Alloys

“…The conventional AB 5 MH alloy performed poorly below´25˝C, but the Co-doped A 2 B 7 superlattice MH alloy can result in significant improvements [82]. Additions of La, Nd, and Si in AB 2 MH alloys can lower the surface charge-transfer resistance (R) at 40˝C to a comparable level with AB 5 MH alloys [23,25,27]. In order to study the effect of Mg addition to the low-temperature performance of AB 2 MH alloys, AC impedance at´40˝C was measured, and R and the double-layer capacitance (C, closely related to the surface reaction area) were calculated from the obtained Cole-Cole plot.…”

“…However, the high-rate dischargeability (HRD) of the AB 2 MH alloys, especially at low temperature, is still significantly inferior to the AB 5 MH alloys because of the relatively low nickel content in the AB 2 alloy [10]. Various additions, including transition metals-Al [11], Cr [12], Co [13], Cu [14,15], Fe [16], Mo [17,18], Zn [19], Pt [20], Pd [21,22], rare earth metals-Y [23], Ce [24], La [25,26], and Nd [27], and others such as Si [28] and B [29], have been used to reduce the surface charge transfer resistance and increase the HRD of AB 2 MH alloys. In this paper, we summarize our findings regarding the use of one of the alkaline earth elements, Mg, as an additive in AB 2 MH alloys.…”