Novel Computational Methods for Studying Charge Transport in Metal-air Batteries

Nicolai Rask Mathiesen

Research output: Book/ReportPh.D. thesis

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The process of electrifying transportation is progressing slowly and the development is mainly carried by the application of Li-ion batteries. Metal-airbatteries are a class of batteries that have the potential to outperform Li-ionbatteries on many key parameters but the technology is still severely limited by problems related to the fundamental electrochemical mechanisms. One of the primary challenges is understanding and improving the charge transport properties of the discharge products. In this thesis, density functional theory (DFT) based calculations are performed and developed to investigate the charge transport in discharge products of alkali metal-air batteries. 

Alkali per- and superoxides are the primary discharge products in alkali metal-air batteries. Their structural and electronic properties, including the intrinsic conductivities, have not been systematically determined yet. To fill the gaps, the intrinsic conductivity ofLiO2 and KO2 is calculated. They are found to be electrical insulators with a very low intrinsic conductivity. This strengthen the conclusion that the intrinsic conductivity of the discharge products, in general, is too low to support the charge transport required by a practical metal-air battery.

The nudged elastic band method (NEB) is widely used to calculate activation barriers of transitions. Here, it is showed that for reflection symmetric transitions, NEB calculations can be performed faster if that symmetry is exploited and an implementation of the method is presented. 

Polaronic transport is considered the main electronic charge transport mechanism in alkali per- and superoxides. However, their mobilities have only been estimated using methods assuming an adiabatic process. Here, the influence of nonadiabatic effects of polaronic transport inLi2O2 is investigated using constrained DFT and Marcus theory. The polaronic transport is found to be highly nonadiabatic and is estimated to be significantly slower when including these effects. As the polaronic transport mechanism basically is the same in all the alkali per- and superoxides, nonadiabatic effects can be expected to be of similar importance in these materials.

Original languageEnglish
PublisherTechnical University of Denmark
Number of pages214
ISBN (Print)978-87-92986-84-9
Publication statusPublished - 2019


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