Investigation of the Structural and Electrochemical Properties of Superstoichiometric Ti-Zr-V-Mn-Cr-Ni Hydrogen Storage Alloys

Abstract

In this paper, the structural and electrochemical properties of the superstoichiometric (Ti 0.8 Zr 0.2 )(V 0.533 Mn 0.107 Cr 0.16 Ni 0.2 ) x ͑x ϭ 2, 3, 4, 5, 6͒ hydrogen storage alloys have been studied systematically. It is found by X-ray diffraction and energy dispersive spectra analysis that all these alloys mainly consist of two phases, a C14 Laves phase with hexagonal structure and a V-based solid solution phase with body-centered cubic structure. The lattice parameters and thus the cell volumes of the two phases all decrease when x is increased. The electrochemical measurements indicate that the maximum discharge capacity, the discharge equilibrium potential, the high rate dischargeability, the cyclic stability, the exchange current density I 0 , and the limiting current density I L of the alloys all increase with increasing x from 2 to 5. When x reaches 6, the discharge equilibrium potential, the high rate dischargeability, and the cyclic stability are still increasing proportionately, while the maximum discharge capacity, the exchange current density I 0 , and the limiting current density I L all decrease. Furthermore, the alloy electrodes are activated with more difficulty for the alloys with higher stoichiometry x. Consequently, we believe that the superstoichiometry is an effective way to improve the overall electrochemical properties of the Ti-based Laves-phase hydrogen storage alloys used for the negative electrodes of the Ni-MH secondary batteries.In recent years, nickel-metal hydride ͑Ni-MH͒ secondary batteries have been widely studied and used due to their higher capacity, higher high rate dischargeability, better cycling property, and environmental compatibility compared with the Ni-Cd batteries. 1-5 In recent decades, many hydrogen storage alloys have been tried and studied, including the rare earth-based AB 5 type alloys, 6 the Ti, Zr-based or Zr, Ti-based AB 2 type alloys, 7,8 the Mg-based alloys, 9 and the V-based solid solutions. 10 Because of the comparatively low discharge capacity of the rare earth-based AB 5 type alloys and poor cyclic stability of Mg-based alloys, people are now searching for new hydrogen storage alloys with higher capacity and long cycle life, among the Ti-or Zr-based alloys and the V-based solid solution alloys. For V-based solid solution, though it has a rather high discharge capacity, its cyclic stability is still not adequate and its high rate dischargeability is also not ideal. 11 The Ti-or Zr-based alloys also have many problems. It is considered that the nonstoichiometry is an effective technique for changing the electrochemical properties of the hydrogen storage alloys by a special doping and multicomponent alloying. 12-18 Lee et al. 12 formulated a kind of hypostoichiometric Zr-based hydrogen storage alloys, which appeared very promising. Notten et al. 13 found that the high rate dischargeability of over-stoichiometric La 0.8 Nd 0.2 Ni 3.0 Co 2.4 Si 0.1 (AB 5.5 ͒ alloy electrode was much higher than that of the stoichiometric La 0.8 Nd 0.2 Ni 2.5 Co 2.4 Si 0.1...

Crystallographic and Electrochemical Characteristics of La0.7Mg0.3Ni5.0−x(Al0.5Mo0.5)x Hydrogen‐Storage Alloys

“…When the overpotential is changed within a small range, the polarisation resistance R p can be estimated from the slope of the linear polarisation curve. Then the I 0 is calculated from the value of R p according to Equation (1). The obtained values of I 0 and R p are summarised in Table 5.…”

“…[1][2][3] Besides the merits of higher energy density, higher charge and discharge ability, and longer charge/discharge cyclic life, the Ni-MH battery also has a smaller memory effect and causes less environmental pollution compared with the rechargeable nickel-cadmium battery. [4][5][6] To date, almost all commercial Ni-MH batteries employ AB 5 type alloys as negative electrode materials because of their good overall electrode properties.…”

Electrochemical properties of Ti0.17Zr0.08V0.35Cr0.10Ni0.30 alloy electrode

“…Takahashi [1,2] reported that hydrogen storage alloys, V 3 TiNi 0.56 and V 3 TiNi 0.56 Hf 0.24 had higher discharge capacity than AB 5 type alloy and Ti 22 V 66 Ni 12 had discharge capacity up to 800 mAh g )1 at 293 K. Thereafter, the properties of TiV 2.1 Ni x alloy electrodes were studied and it was shown that this negative electrode had higher discharge capacity than the above-mentioned alloy [3,4]. Pan et al [5,6] studied (Ti 0.8 Zr 0.2 )(V 0.533 Mn 0.107 Cr 0.16 Ni 0.2 ) (x=2, 3, 4, 5, 6, 7) multiphase hydrogen storage electrode alloys and pointed out that the alloys had good cycling stability and high rate dischargeability at 303 K. Up to now, the influence of temperature on the discharge capacity of the multiphase alloy has received little attention.…”

Crystallographic and Electrochemical Characteristics ofLa0.7Mg0.3Ni4.5–x(Al0.5Mo0.5)x (x = 0–0.8) Hydrogen Storage Alloys

“…[7] However, the electrochemical capacity of the AB 5 -type alloys is limited by the single CaCu 5 -type hexagonal structure; [8] the energy densities of the Ni-MH batteries cannot compete favorably with some other advanced secondary batteries. Therefore, new types of alloys with higher energy densities, faster activation, better rate dischargeabilities, and lower cost are urgently needed to replace the conventional rare-earth-based AB 5 -type alloys. [9] charge current density of 1200 mA/g, the high-rate dischargeability of the alloy electrodes increases linearly from 47.2 % (x = 0) to 73.8% (x = 0.8).…”