Simon Loftager Ph.D. defense 31/10/2016

PhD defence: Computer modelling of battery materials

Tuesday 01 Nov 16

Computational investigations of interfacial transport mechanisms and charge localization in positive-electrode materials

Main supervisor: Tejs Vegge

Co-supervisor: Juan Maria García Lastra

The Ph.D. study was a part of the project Hi-C, ‘Novel in situ and in operando techniques for characterization of interfaces in electrochemical storage systems’, which is supported by the EU 7th Framework Programme for Research and Technological Development.
On 31 October 2016 Simon Loftager successfully defended his PhD thesis with the title “Computational investigations of interfacial transport mechanisms and charge localization in positive-electrode materials”.

Even though lithium-ion batteries are everywhere, from mobile phones to electrical vehicles, it is still a challenge to be able to store enough energy in them. A battery consists of two electrodes separated by an electrolyte. When the battery is being charged, an applied voltage makes lithium ions move from the positive electrode through the electrolyte into the negative electrode. When the battery is discharged the opposite process occurs, accompanied by an electrical current in the external circuit. The mobility of the lithium ions and electrons in the positive electrode is decisive for many of the properties of the battery. For the past three years Simon Loftager has studied the mechanisms at the atomic scale which determine the transport of ions and electrons in the electrode.

It turns out that an electrode is a complicated physico-chemical system which not only has interfaces to other materials in the battery but also can contain a number of internal interfaces between different phases of the electrode material. The transport properties depend both on the interfaces and on the phases themselves. Simon has studied these questions theoretically using Density Functional Theory which allows one to calculate how Li ions can move through an interface or how stable two different phases are with respect to each other.

Simon Loftager Ph.D. defense 31/10/2016Simon has primarily focused on the promising electrode material lithium iron borate (LiFeBO3). However, in practice its electrochemical performance has been lower than expected. Simon has been able to show that this is due to the formation of an intermediate phase, Li0.5FeBO3, which has significantly poorer transport properties than LiFeBO3. On the other hand, the interfaces between the two phases do not seem to have any influence on the electrode properties. Simon has also studied the effect of the protective layer of carbon normally deposited on lithium iron borate. He has investigated how this layer influences the transport of lithium ions, and in particular he has identified a novel configuration of the carbon layer which optimises the transport across the interface layer.

Even after three years of intense battery studies Simon has not tired of the field: He has just been hired at DTU Energy in a postdoc position where he is to study an entirely new class of electrode materials as part of the EU project LiRichFCC.

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