Fe-Substitution for Ni in Misch Metal-Based Superlattice Hydrogen Absorbing Alloys—Part 2. Ni/MH Battery Performance and Failure Mechanisms

Abstract

Abstract:The electrochemical performance and failure mechanisms of Ni/MH batteries made with a series of the Fe-substituted A 2 B 7 superlattice alloys as the negative electrodes were investigated. The incorporation of Fe does not lead to improved cell capacity or cycle life at either room or low temperature, although Fe promotes the formation of a favorable Ce 2 Ni 7 phase. Fe-substitution was found to inhibit leaching of Al from the metal hydride negative electrode and promote leaching of Co, which could potentially extend the cycle life of the positive electrode. The failure mechanisms of the cycled cells with the Fe-substituted superlattice hydrogen absorbing alloys were analyzed by scanning electron microscopy, energy dispersive spectroscopy and inductively coupled plasma analysis. The failure of cells with Fe-free and low Fe-content alloys is mainly attributed to the pulverization of the metal hydride alloy. Meanwhile, severe oxidation/corrosion of the negative electrode is observed for cells with high Fe-content alloys, resulting in increased internal cell resistance, formation of micro-shortages in the separator and eventual cell failure.Keywords: metal hydride (MH); nickel/metal hydride (Ni/MH) battery; hydrogen absorbing alloy (HAA); superlattice alloy; failure mechanism

Fe-Substitution for Ni in Misch Metal-Based Superlattice Hydrogen Absorbing Alloys—Part 1. Structural, Hydrogen Storage, and Electrochemical Properties

“…Since any investigation on the effects of Fe incorporation in the misch metal-based superlattice HAA was absent, such results are very desirable in order to further improve the electrochemical properties of the superlattice HAA. While this paper (Part 1) summarizes the results of structural, gaseous phase, and electrochemical (in half-cell configuration) studies on the Fe-substituted misch metal-based superlattice alloys, the performance and failure analysis of the Ni/MH batteries made using these alloys will be discussed in another publication (Part 2, [44]).…”

Research in Nickel/Metal Hydride Batteries 2017

“…In the C-size cell, performances of AB 2 (between C14 and C15) [27], a Fe-free [28] and a Fe-doped [29] superlattice MH alloys were measured, and that results can be summarized as follows: C15-based MH alloy was more suitable for high-rate application comparing to those from C14 alloy and confirm previous half-cell results [16], superlattice alloy showed better high-rate and low-temperature performances comparing to those of AB 5 MH alloy, and Fe in the superlattice alloy can extend the cycle life by preventing Al-leaching from the negative electrode. In the newly developed pouch type cell, the high-capacity core-shell Ni(OH) 2 was compared to the conventional single-phase Ni(OH) 2 , and lower impedance and better charge retention were observed [30].…”

Effects of Molybdenum to the Hydrogen Storage and Electrochemical Properties of Superlattice Metal Hydride Alloy

“…doi: https://doi.org/10.24218/msear.2018. 25. metal (Mm, mixtures of a few REs) based superlattice alloys, we have conducted a few substitution works, such as Al [14], Mn [15,16], Fe [17,18], and Co [19−21], and reached the following conclusions: Al improves the hydrogen-storage (H-storage) kinetics and enhances the cycle stability; a small amount of Mn (2.3 at%) improves the HRD and charge retention performance; Fe promotes the formation of the desirable Nd 2 Ni 7 phase; and Co provides improved low-temperature performance.…”