Ageing analysis and asymmetric stress considerations for small format cylindrical cells for wearable electronic devices

JOURNAL OF POWER SOURCES

卷:472

Article

Tan, C. C.¹  Walker, M.²  Remy, G.¹  Kourra, N.¹  Maddar, F.¹  Dixon, S.¹  Williams, M.¹  Loveridge, M. J.¹ 

[1] Univ Warwick, Warwick Mfg Grp WMG, Coventry CV4 7AL, W Midlands, England

[2] Univ Warwick, Dept Phys, Coventry CV4 7AL, W Midlands, England

关键词: Commercial Li-ion battery;    Degradation;    LiCoO2;    Charge transfer resistance;    LiF;    Stress asymmetry;   

DOI  :  10.1016/j.jpowsour.2020.228626

来源: Elsevier

【 摘 要 】

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 degrees 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.

【 授权许可】

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