In situ investigation of commercial Ni(OH) 2 and LaNi 5 -based electrodes by neutron powder diffraction
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Matthew Roberts Department of Materials Chemistry, Ångström Laboratory, Uppsala University, Uppsala 751 21, Sweden
Dag Noréus Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 106 91, Sweden
Ulrika Lagerqvist Nilar Svenska AB, Gavle 800 08, Sweden
Ronald I. Smith The ISIS Facility, STFC Rutherford Appleton Laboratory, Oxfordshire 11 0QX, UK
Gunnar Svensson Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 106 91, Sweden
Stefan T. Norberg and Sten G. Eriksson Department of Chemical and Biological Engineering, Chalmers University of Technology, Sweden 412 96, Sweden
Stephen Hull The ISIS Facility, STFC Rutherford Appleton Laboratory, Oxfordshire 11 0QX, UK (Received 13 June 2014; accepted 3 October 2014)
Electrochemical reactions at both positive and negative electrodes in a nickel metal hydride (Ni-MH) battery during charge have been investigated by in situ neutron powder diffraction. Commercially available b-Ni(OH)2 and LaNi 5 -based powders were used in this experiment as positive and negative electrodes, respectively. Exchange of hydrogen by deuterium for the b-Ni(OH) 2 electrode was achieved by ex situ cycling of the cell prior to in situ measurements. Neutron diffraction data collected in situ show that the largest amount of deuterium contained at the positive electrode is de-intercalated from the electrode with no phase transformation involved up to ;100 mA h/g and, in addition, the 110 peak width for the positive electrode increases on charge. The negative electrode of composition MmNi 3.6 Al0.4 Mn0.3 Co 0.7 , where Mm 5 Mischmetal, exhibits a phase transformation to an intermediate hydride c phase first and then to the b phase on charge. Unit cell dimensions and phase fractions have been investigated by Rietveld refinement of the crystal structure. I. INTRODUCTION
Nickel-metal hydride batteries (Ni-MH) appeared on the market toward the end of the 1980s, replacing other nickel-based rechargeable batteries such as the nickelcadmium system.1 In the Ni-MH battery, the hydrogen at the positive electrode is de-intercalated during charge and absorbed at the metal alloy (M) working as a “hydrogen sponge”. The half-cell reactions at the positive and negative electrodes are presented below. The use of metal hydride (MH) material as the anode
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.317 J. Mater. Res., Vol. 30, No. 3, Feb 14, 2015
http://journals.cambridge.org
increased the storage battery capacity and extended the cycle life with respect to Ni–Cd and Ni–Fe batteries. Ni-MH batteries compete directly with Li-ion batteries even though they have lower energy densities. Applications range from portable electronics to hybrid electric vehicles e.g., the Toyota Prius is powered by a 27 kW Ni-MH battery2 NiðOHÞ2 þ OH 4NiOOH þ H2 O
þ e ðpositive electrodeÞ
M þ H2 O þ e 4MH þ OH ðnegative electrodeÞ NiðOHÞ2 þ M 4NiOOH þ MH ðoverallÞ
Ó Materials Research Society 2014. This is an Open A
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