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

Abstract

C14 Laves phase alloys play a significant role in improving the performance of nickel/metal hydride batteries, which currently dominate the 1.2 V consumer-type rechargeable battery market and those for hybrid electric vehicles. In the current study, the properties of C14 Laves phase based metal hydride alloys are reviewed in relation to their electrochemical applications. Various preparation methods and failure mechanisms of the C14 Laves phase based metal hydride alloys, and the influence of all elements on the electrochemical performance, are discussed. The contributions of some commonly used constituting elements are compared to performance requirements. The importance of stoichiometry and its impact on electrochemical properties is also included. At the end, a discussion section addresses historical hurdles, previous trials, and future directions for implementing C14 Laves phase based metal hydride alloys in commercial nickel/metal hydride batteries.

Effects of Alkaline Pre-Etching to Metal Hydride Alloys

“…The main difference between these two preparation methods is the size of ingot. While the former is usually used in large production (1-1000 kg), the latter is mostly used in laboratories (5-200 g) [15]. Some alloys went through annealing either in vacuum or Ar.…”

“…A few pre-activation processes, such as surface fluorination, alkaline bath, acid etch, mechanical alloying, etc., were proposed to shorten the activation process and improve the electrochemical performance of the MH alloys (see a review in [15]). Among these processes, the alkaline bath is very effective in dissolving the native oxide, so as to form a porous oxide surface with catalytic Ni clusters imbedded [13,[16][17][18][19][20][21][22] and to increase the surface reactive area [23].…”

Effects of Boron-Incorporation in a V-Containing Zr-Based AB2 Metal Hydride Alloy

“…Slope factor (SF), defined as the ratio of desorption capacity between 0.01 and 0.5 MPa to total reversible capacity [6,17,22], is an indicator of the degree of disorder (DOD) in the MH alloy [38] and smaller in a more slanted isotherm. SF measured at 30 • C is listed in the fifth column in Table 4 and shows a decreasing trend with the increase in the boron content.…”

“…Two commonly used stoichiometries in Ni/MH batteries are AB 2 and AB 5 , where the A-site is occupied by larger elements with stronger affinities with hydrogen, and the B-site elements are relatively smaller and have the tendency to weaken the alloy's average metal-hydrogen bond strength [3]. Nevertheless, flexibility in stoichiometry [4,5] and abundantly available secondary phases [6] in the AB 2 metal hydride (MH) alloy allow for fine tailoring in chemical composition to fulfill the stringent demands from different applications. Among various types of AB 2 MH alloys, one based on the C14 Laves phase-an intermetallic phase with an AB 2 stoichiometry-is commonly used as the negative electrode active material of the Ni/MH battery [6].…”

“…Nevertheless, flexibility in stoichiometry [4,5] and abundantly available secondary phases [6] in the AB 2 metal hydride (MH) alloy allow for fine tailoring in chemical composition to fulfill the stringent demands from different applications. Among various types of AB 2 MH alloys, one based on the C14 Laves phase-an intermetallic phase with an AB 2 stoichiometry-is commonly used as the negative electrode active material of the Ni/MH battery [6]. Laves phases, named after Fritz Laves , have three different classes: a cubic MgCu 2 (C15), a hexagonal MgZn 2 (C14), and a dihexagonal MgNi 2 (C36) [7].…”