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Author
Date
2021Type
- Doctoral Thesis
ETH Bibliography
yes
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Abstract
To be able to solve the 21st century’s renewable energy challenge, energy storage is key. While numerous strategies have been proposed and implemented for stationary energy storage, so far only lithium ion batterieshave had large success for mobile applications such as cars and smartphones. However, to be able to further penetrate the market, improvements in charging speeds are critical. Therefore, strategies to characterize and reduce ionic and electronic resistances at the material interfaces are required. This doctoral thesis introduces a new strategy to quantify ion diffusion at interfaces of commercially relevant materials by applying a combination of i) morphology controlled synthesis, ii) experiments at large scale facilities, iii) \textit{ab initio} molecular modelling, and iv) electrochemical measurements. We provide a full picture of the underlying processes that induce changes in charge dynamics hence paving the way to new strategies to engineer interfaces.
Part 1 introduces the challenges in LIB technology and what large scale facilities can contribute towards their solution. Thanks to the large public attention that LIBs have attracted, numerous new experiments at synchrotrons and other particle accelerators have been adapted to the special needs of lithium ion batteries in the last decade, creating new opportunities for an understanding and optimization of the complex interactions within the LIB.
Part 2 focuses on the morphology controlled hydrothermal synthesis of LiFePO4 platelet particles. We introduce a novel low-temperature synthesis of micrometer sized platelet particles that maintain a high crystallinity. We end up with a size series of particles with different surface to volume ratios, offering the possibility to track surface effects. By introducing coatings, we can then actively change the surface environment.
Part 3 studies the effect of the surface reconstruction on lattice vibrations. Performing inelastic neutron scattering experiments on the size series synthesized earlier, we can separate bulk and surface effects. We find changes in the Fe-O and Li-O phonon modes at the LiFePO4 - carbon interface hence suggesting changes in the charge dynamics. Following up on these results, we quantify the activation barrier of interface diffusion in Part 4 via a combination of muon spin spectroscopy, electrochemical characterizations, and nudged elastic band simulations. With an activation barrier of ~180 meV, the Li diffusion barrier through the LiFePO4 (010) surface is strongly reduced.
In Part 5 we add more complexity to our system by characterizing the impact of surface terminations to charge dynamics. Extending our approach to electronics, we get important insights in the full mechanism of interface dynamics. We find that the strongly enhanced interface ion dynamics in carbon coatings are in fact a result of enhanced electronic transport that allows for decoupled ion and electron motion. Based on this finding, we rationally engineer particle coatings that can homogeneously (de)lithiate cathode active materials hence creating coatings that allow for longer active material lifetime without affecting charging rate capability. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000510343Publication status
publishedExternal links
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Publisher
ETH ZurichSubject
Li ion batteries; Neutron scattering; Muon spin spectroscopy; Ion dynamics; Surface modificationOrganisational unit
03895 - Wood, Vanessa / Wood, Vanessa
Funding
680070 - Development of Quantitative Metrologies to Guide Lithium Ion Battery Manufacturing (EC)
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ETH Bibliography
yes
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