Reid, Hamish T;
(2025)
Linking degradation and safety of
lithium-ion batteries.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Currently, Li ion batteries are the most common energy source used in portable electronic devices, but the electric vehicle sector is expected to grow significantly over the next few decades, placing increasing demands on cell performance, durability and safety. With increasing battery size and energy density for the automotive sector, alongside the increased risk of external damage to the battery pack caused by accidents, the inherent safety of battery packs is fundamentally important and must be understood in more detail. Most recent research efforts have been dedicated to understanding the safety performance of cells in the ‘pristine’ state, before they have undergone any degradation that will occur with repeated charge/discharge cycling. As more batteries are manufactured and put into use, there is a pressing need to understand the safety responses of cells throughout their operation lifetimes. In this work, a range of multiscale characterisation techniques are employed to investigate both effects of cycle ageing on battery materials, the key mechanisms during abuse scenarios, and the interplay between cycling and safety performance. X-ray computed tomography is employed for ex-situ and in-situ experimentation. Degradation mechanisms are explored using imaging techniques and electrochemical analysis, before comparing the safety performance of cells in the pristine and aged state. Commercial cells, relevant to the automotive industry, are investigated using electrical and thermal abuse techniques both before and after cycling. In-line mass spectrometry is used to analyse the gasses released during thermal runaway under different conditions. To understand the effects of cathode microstructure on cycling and safety, smaller research-scale pouch cells with both single-crystal and polycrystalline variants of the same material are compared using calorimetry. In order to capture the rapid structural evolution that occurs during cell failure, a bespoke cell heating chamber has been developed and employed in both laboratory and synchrotron-based in-situ X-ray CT imaging. Finally, in collaboration with industry partner Johnson Matthey, a range of materials have been imaged and analysed using high-throughput lab-based micro-CT, with the findings fed-back into research and development. The experiments reported here outline the connections between battery ageing and safety performance, as well as the microstructural characterisation of industrially relevant materials. The relationships between cell architecture at multiple scales is explored, underlining the significance of material and engineering design on battery safety. As the world moves towards vehicle electrification, this work will contribute towards efforts to make batteries safer, more accessible and more affordable for all.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Linking degradation and safety of lithium-ion batteries |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10203874 |
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