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Title: The influence of Mn on the crystallography and electrochemistry of nonstoichiometric AB{sub 5}-type hydride-forming compounds

Abstract

To design Co-free, low-pressure, hydride-forming compounds for application in rechargeable nickel metal hydride batteries, nonstoichiometric AB{sub x} materials were investigated. The influence of both the Mn content and the degree of nonstoichiometry on the crystallography, electrochemical cycling stability, and electrode morphology were studied. The investigated composition was in the range of La(Ni{sub 1{minus}z}Mn{sub z}){sub x} with 5.0 {le} x {le} 6.0 and 0 {le} xz {le} 2.0. The annealing temperature was essential in preparing homogeneous compounds. In agreement with geometric considerations, both the a and c axis of the hexagonal unit cell increase with increasing Mn content. In contrast, the a axis decreases with increasing degree of nonstoichiometry. As proved by neutron-diffraction experiments, the introduction of dumbbell pairs of Ni or Mn atoms on the La positions in the crystal lattice is responsible for this behavior. The electrochemical cycling stability is found to be strongly dependent on both the chemical and nonstoichiometric composition. Electrochemically stable materials are characterized by the absence of a significant particle-size reduction upon electrode cycling, reducing the overall oxidation rate. Unstable materials suffer from severe mechanical cracking through which the oxidation rate is increased. The improved mechanical stability is attributed to the reduced discrete lattice expansion.more » The most stable compound has a partial hydrogen pressure of only 0.1 bar, which matches well with that desirable in practical NiMH batteries. Neutron-diffraction experiments confirmed the hypothesis that La atoms are replaced by dumbbell pairs of Ni, in the case of the binary LaNi{sub 5.4}, and by Mn atoms in the case of the mn-containing nonstoichiometric compounds. Electron-probe microanalyses and density measurements support the dumbbell hypothesis.« less

Authors:
; ;
Publication Date:
Research Org.:
Philips Research Labs., Eindhoven (NL)
OSTI Identifier:
20003194
Resource Type:
Journal Article
Journal Name:
Journal of the Electrochemical Society
Additional Journal Information:
Journal Volume: 146; Journal Issue: 9; Other Information: PBD: Sep 1999
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 25 ENERGY STORAGE; 08 HYDROGEN; CRYSTAL STRUCTURE; NICKEL ALLOYS; LANTHANUM ALLOYS; MANGANESE ALLOYS; STOICHIOMETRY; ELECTRICAL PROPERTIES; NICKEL-HYDROGEN BATTERIES; HYDROGEN STORAGE

Citation Formats

Notten, P.H.L., Latroche, M., and Percheron-Guegan, A. The influence of Mn on the crystallography and electrochemistry of nonstoichiometric AB{sub 5}-type hydride-forming compounds. United States: N. p., 1999. Web. doi:10.1149/1.1392452.
Notten, P.H.L., Latroche, M., & Percheron-Guegan, A. The influence of Mn on the crystallography and electrochemistry of nonstoichiometric AB{sub 5}-type hydride-forming compounds. United States. doi:10.1149/1.1392452.
Notten, P.H.L., Latroche, M., and Percheron-Guegan, A. Wed . "The influence of Mn on the crystallography and electrochemistry of nonstoichiometric AB{sub 5}-type hydride-forming compounds". United States. doi:10.1149/1.1392452.
@article{osti_20003194,
title = {The influence of Mn on the crystallography and electrochemistry of nonstoichiometric AB{sub 5}-type hydride-forming compounds},
author = {Notten, P.H.L. and Latroche, M. and Percheron-Guegan, A.},
abstractNote = {To design Co-free, low-pressure, hydride-forming compounds for application in rechargeable nickel metal hydride batteries, nonstoichiometric AB{sub x} materials were investigated. The influence of both the Mn content and the degree of nonstoichiometry on the crystallography, electrochemical cycling stability, and electrode morphology were studied. The investigated composition was in the range of La(Ni{sub 1{minus}z}Mn{sub z}){sub x} with 5.0 {le} x {le} 6.0 and 0 {le} xz {le} 2.0. The annealing temperature was essential in preparing homogeneous compounds. In agreement with geometric considerations, both the a and c axis of the hexagonal unit cell increase with increasing Mn content. In contrast, the a axis decreases with increasing degree of nonstoichiometry. As proved by neutron-diffraction experiments, the introduction of dumbbell pairs of Ni or Mn atoms on the La positions in the crystal lattice is responsible for this behavior. The electrochemical cycling stability is found to be strongly dependent on both the chemical and nonstoichiometric composition. Electrochemically stable materials are characterized by the absence of a significant particle-size reduction upon electrode cycling, reducing the overall oxidation rate. Unstable materials suffer from severe mechanical cracking through which the oxidation rate is increased. The improved mechanical stability is attributed to the reduced discrete lattice expansion. The most stable compound has a partial hydrogen pressure of only 0.1 bar, which matches well with that desirable in practical NiMH batteries. Neutron-diffraction experiments confirmed the hypothesis that La atoms are replaced by dumbbell pairs of Ni, in the case of the binary LaNi{sub 5.4}, and by Mn atoms in the case of the mn-containing nonstoichiometric compounds. Electron-probe microanalyses and density measurements support the dumbbell hypothesis.},
doi = {10.1149/1.1392452},
journal = {Journal of the Electrochemical Society},
number = 9,
volume = 146,
place = {United States},
year = {1999},
month = {9}
}