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Development of metal hydride surface structures for high power NiMH batteries: Also extended cycle-life and lead to more effective recycling methods
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

By combining alkaline etching of hydrogen storage alloys or their hydrides with a controlled oxidation, it was possible to improve reaction kinetics and accelerate activation of MH-electrodes. Both AB5 and AB2 alloys were studied where A is mixtures of rare earth elements for AB5 alloys and titanium and/or vanadium, zirconium for AB2 alloys; nickel contributes the major part of B. With SEM and TEM studies the surface could be described as consisting of several phases where an interphase with active Ni-containing cluster protected the inner metallic hydrogen storage part of the powder particles. These catalytic Ni-clusters presumably lead to the fast activation and high discharge capacity of alloy.

This interphase was observed to be stable enough to allow us to develop a method, where we could add pure oxygen to a NiMH battery pack in order to regenerate the amount of electrolyte that was lost during long time cycling of the battery. Meanwhile, the method will rebalance the electrodes mitigating excessive pressures during over charge. Therefore, the internal resistance of cells can be reduced and cycle life will increase.

It was also shown that the stable interphase could survive a mild ball milling or sonication which enabled us to upcycle material from spent NiMH batteries into a better working MH-electrodes with improved kinetics and activation properties. Reuse of ball-milled or sonicated material could serve as a simple recycling alternative to energy-demanding metallurgical smelting methods and chemical consuming hydrometallurgical recycling processes, where the possibilities of up-scaling further favour the less complex mechanical treatments. The stable but catalytic interphase protecting the inner particles indicates that the MH-electrode material may perform better in its second life in a new NiMH battery.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University , 2018. , p. 44
Keywords [en]
Metal hydrides, NiMH batteries, Surface treatment, Ni clusters, Rare earths hydroxides, Oxygen, Hydrogen
National Category
Inorganic Chemistry Materials Chemistry
Research subject
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-154581ISBN: 978-91-7797-218-1 (print)ISBN: 978-91-7797-219-8 (electronic)OAI: oai:DiVA.org:su-154581DiVA, id: diva2:1194626
Public defence
2018-12-10, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2018-11-15 Created: 2018-04-03 Last updated: 2018-11-09Bibliographically approved
List of papers
1. Improved NiMH performance by a surface treatment that creates magnetic Ni-clusters
Open this publication in new window or tab >>Improved NiMH performance by a surface treatment that creates magnetic Ni-clusters
2016 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 41, no 23, p. 9933-9938Article in journal (Refereed) Published
Abstract [en]

A surface treatment method has been developed to activate the surface of an AB(5) type (La-20 Ce-7 Pr-1 Nd-4 Al-2 Mn-5 Co-6 Ni-55) alloy. In the process the surface is covered with a porous surface layer containing needle shaped rare earth hydroxides after etching by a potassium hydroxide solution. TEM studies show in addition the presence of a denser surface oxide layer with embedded Ni containing clusters covering the bulk alloy. The magnetic properties of the alloy powders change with the surface treatment. In addition to a paramagnetic component of the bulk alloy, surface treated alloy also displays superparamagnetic and ferromagnetic properties. In electrochemical half-cell tests, the alloy shows better high-rate dischargeability with increasing presence of magnetic clusters in the metal hydride particles surface.

Keywords
Metal hydrides, NiMH batteries, Surface treatment, Ni clusters, Discharge kinetics, Rare earths hydroxides
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-132397 (URN)10.1016/j.ijhydene.2016.01.145 (DOI)000378359400029 ()
Conference
1st International Symposium on Materials for Energy Storage and Conversion (ESC-IS), Middle East Technical University, Ankara, Turkey, September 07-09, 2015
Available from: 2016-08-15 Created: 2016-08-11 Last updated: 2018-04-04Bibliographically approved
2. Activation behavior of an AB(2) type metal hydride alloy for NiMH batteries
Open this publication in new window or tab >>Activation behavior of an AB(2) type metal hydride alloy for NiMH batteries
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2016 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 41, no 23, p. 9948-9953Article in journal (Refereed) Published
Abstract [en]

Activation behavior of an AB(2), namely (Ti0.36Zr0.64) (V0.15Ni0.58Mn0.20Cr0.07)(2) Laves phase alloy, was investigated with regards to; particle size, ball milling and hot alkaline treatments. Galvanostatic cycling in open cells showed that an untreated alloy initially had almost no capacity, but reached a value of 220 mAh/g after 14 cycles. Experiments with different particle sizes showed that coarse particles activate faster yielding an improved capacity. In terms of activation more pronounced effect was obtained with boiling the alloy powder in a hot KOH solution. A capacity in excess of 300 mAh/g is reached in the first cycle after a 20 min treatment. The capacity was highest after 80 min, yielding a value of 390 mAh/g well above that expected from the gas-phase storage in the alloy. This was attributed to the formation of rough surface in the powder, which may stabilize hydrogen bubbles allowing pressures above 1 atm to be reached locally in the surface.

Keywords
Metal hydride, Laves phase, NiMH batteries, Activation, Particle size, Hot alkaline treatment
National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-132398 (URN)10.1016/j.ijhydene.2016.03.196 (DOI)000378359400031 ()
Conference
1st International Symposium on Materials for Energy Storage and Conversion (ESC-IS), Middle Eeast Technical University, Ankara, Turkey, September 07-09, 2015
Available from: 2016-08-15 Created: 2016-08-11 Last updated: 2018-04-04Bibliographically approved
3. Increasing NiMH battery cycle life with oxygen
Open this publication in new window or tab >>Increasing NiMH battery cycle life with oxygen
2018 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 43, no 40, p. 18626-18631Article in journal (Refereed) Published
Abstract [en]

Nickel-Metal Hydride batteries (NiMH) have long cycle life. But in the end corrosion of the metal hydride is detrimental for life expectancy. Corrosion reduces the metal hydride capacity, but more severely it consumes water in the electrolyte resulting in increased internal resistance, which is the main cause for cell failure.

The corrosion, further, evolves hydrogen, causing an unbalance between anode and cathode, leading to premature internal pressure increase when the cells are approaching end of charge. This accelerates the drying out, if the cells vent through the safety valve.

In this study, a controlled addition of oxygen was used to rebalance the electrodes and replenish the electrolyte – as the added oxygen reacts with hydrogen that was formed during the corrosion process. Thus, the two most detrimental factors in cell ageing can be mitigated. To fully restore the electrolyte content as well as electrode balance, both oxygen and hydrogen are needed to compensate for the loss to hydroxide ions OH formed in the corrosion process. A proper optimization of the gas additions combined with a cell design including an excess amount of MH-alloy to compensate for the corrosion can substantially increase the cycle life of NiMH batteries.

Keywords
NiMH batteries, Electrochemistry, Cell balancing, Oxygen, Hydrogen
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-154736 (URN)10.1016/j.ijhydene.2018.03.020 (DOI)000447479100009 ()
Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-11-12Bibliographically approved
4. Upcycling of spent NiMH battery material - Reconditioned battery alloys show faster activation and reaction kinetics than pristine alloys as well as longer cycle life due to lower corrosion rates
Open this publication in new window or tab >>Upcycling of spent NiMH battery material - Reconditioned battery alloys show faster activation and reaction kinetics than pristine alloys as well as longer cycle life due to lower corrosion rates
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(English)Manuscript (preprint) (Other academic)
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-154738 (URN)
Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-10-24Bibliographically approved

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