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Open AccessFeature PaperArticle

Upcycling of Spent NiMH Battery Material—Reconditioned Battery Alloys Show Faster Activation and Reaction Kinetics than Pristine Alloys

1
Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden
2
Nilar AB, Box 8020, SE-800 08 Gävle, Sweden
*
Author to whom correspondence should be addressed.
Academic Editors: Ewa C. E. Rönnebro and Giuseppe Cirillo
Molecules 2020, 25(10), 2338; https://doi.org/10.3390/molecules25102338
Received: 25 March 2020 / Revised: 13 May 2020 / Accepted: 15 May 2020 / Published: 17 May 2020
(This article belongs to the Special Issue Advances in Hydrogen Storage Materials for Energy Utilization)
During formation and cycling of nickel–metal hydride (NiMH cells), surface corrosion on the metal hydride particles forms a porous outer layer of needle-shaped rare-earth hydroxide crystals. Under this layer, a denser but thinner oxidized layer protects the inner metallic part of the MH electrode powder particles. Nano-sized nickel-containing clusters that are assumed to promote the charge and discharge reaction kinetics are also formed here. In this study, mechanical treatments are tested to recycle hydrogen storage alloys from spent NiMH batteries. This removes the outer corroded surface of the alloy particles, while maintaining the catalytic properties of the surface. Scanning electron microscopy images and powder X-ray diffraction measurements show that the corrosion layer can be partly removed by ball milling or sonication, combined with a simple washing procedure. The reconditioned alloy powders exhibit improved high rate properties and activate more quickly than the pristine alloy. This indicates that the protective interphase layer created on the alloy particle during their earlier cycling is rather stable. The larger active surface that is created by the mechanical impact on the surface by the treatments also improves the kinetic properties. Similarly, the mechanical strain during cycling cracks the alloy particles into finer fragments. However, some of these particles form agglomerates, reducing the accessibility for the electrolyte and rendering them inactive. The mechanical treatment also separates the agglomerates and thus further promotes reaction kinetics in the upcycled material. Altogether, this suggests that the MH electrode material can perform better in its second life in a new battery. View Full-Text
Keywords: metal hydride; NiMH batteries; regeneration; reconditioning; sonication; ball-milling; acid washing; alkaline washing metal hydride; NiMH batteries; regeneration; reconditioning; sonication; ball-milling; acid washing; alkaline washing
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Shen, Y.; Svensson Grape, E.; Noréus, D.; Widenkvist, E.; Starborg, S. Upcycling of Spent NiMH Battery Material—Reconditioned Battery Alloys Show Faster Activation and Reaction Kinetics than Pristine Alloys. Molecules 2020, 25, 2338.

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