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Ageing analysis and asymmetric stress considerations for small format cylindrical cells for wearable electronic devices
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Tan, Chaou C., Walker, Marc, Remy, Guillaume , Kourra, Nadia, Maddar, Faduma, Dixon, Steve M., Williams, Mark A. and Loveridge, Melanie (2020) Ageing analysis and asymmetric stress considerations for small format cylindrical cells for wearable electronic devices. Journal of Power Sources, 472 . 228626. doi:10.1016/j.jpowsour.2020.228626
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Official URL: http://dx.doi.org/10.1016/j.jpowsour.2020.228626
Abstract
Performance assessments on miniature cylindrical cells used in Fitbit Flex 2 fitness trackers have been performed to understand the dominant ageing modes and small format implications. We utilise electrochemical testing, x-ray photoelectron Spectroscopy (XPS), x-ray computed tomography (XCT) and scanning electron microscopy (SEM), to reveal device and component structural features and changes. The cell maintains 82% cell capacity retention after 500 continuous charging and discharging cycles at 3.0–4.35 V, 0.75C rate at 20 °C. The anode shows severe delamination due to high bending stress exerted on the cell components, however this seemingly has minimum impact on the electrochemical performance if the coating is sufficiently compressed in the jelly roll with a good electrical contact. After ageing, the surface layers continue to grow, with more LiF found on the cathode and anode. The formation of LiF is discussed and we suggest the main ageing mechanism of the Fitbit cell is related to increasing charge transfer resistance due to the transportation of Li+ ions being inhibited by the thicker surface layer, which contains LiF. That preferential delamination on the inner sides of the electrode coatings was observed consistently opens up an interesting avenues for advances in cylindrical cell manufacturing at large.
| Item Type: | Journal Article | |||||||||
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| Subjects: | T Technology > TK Electrical engineering. Electronics Nuclear engineering | |||||||||
| Divisions: | Faculty of Science > Physics Faculty of Science > WMG (Formerly the Warwick Manufacturing Group) |
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| Library of Congress Subject Headings (LCSH): | Lithium ion batteries, Lithium ion batteries -- Deterioration, Strains and stresses, Wearable technology | |||||||||
| Journal or Publication Title: | Journal of Power Sources | |||||||||
| Publisher: | Elsevier S.A. | |||||||||
| ISSN: | 0378-7753 | |||||||||
| Official Date: | 1 October 2020 | |||||||||
| Dates: |
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| Date of first compliant deposit: | 30 July 2020 | |||||||||
| Volume: | 472 | |||||||||
| Article Number: | 228626 | |||||||||
| DOI: | 10.1016/j.jpowsour.2020.228626 | |||||||||
| Status: | Peer Reviewed | |||||||||
| Publication Status: | Published | |||||||||
| Access rights to Published version: | Restricted or Subscription Access | |||||||||
| RIOXX Funder/Project Grant: |
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