An Explanation of the Ageing Mechanism of Li-Ion Batteries by Metallographic and Material Analysis

Gorse, S.; Kugler, Benoit; Samtleben, T.; Waldmann, Thomas; Wohlfahrt‐Mehrens, M.; Schneider, Gerhard; Knoblauch, Volker

doi:10.3139/147.110325

Cited by 16 publications

(24 citation statements)

References 14 publications

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“…Such deformations were observed before in different types of commercial cells which usually also utilize welded tabs. [2,[14][15][16][17][18] The data of Bach et al suggested that pressure inhomogeneities in cylindrical cells lead to local Li deposition on the anode, which spreads out over the whole anode area when cells are further cycled, leading to a sudden capacity drop. [14] Figure 9 shows such a sudden drop of capacity after %700 cycles for the cells with welded tabs, however, not for the cells with foil tabs.…”

Section: Improvement Of Cycle Life By Foil Tab Designmentioning

confidence: 99%

Effects of Tab Design in 21700 Li‐Ion Cells: Improvements of Cell Impedance, Rate Capability, and Cycling Aging

et al. 2022

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Li‐ion cells of the industrially relevant 21700 format are investigated experimentally by systematic variation of their tab design. To observe the effects of the tab design only, the cells are built on pilot scale using the same electrodes, electrolyte, and separator. Tabs are varied regarding 1) conventionally welded tabs and 2) tabs made from the electrodes’ foils (“foil tabs”), as well as the tab number. Conclusions are drawn on cell impedances, rate capability (0.5C–3C), heating behavior, and cycling aging. Cells with a multitab design show a reduced impedance (1 kHz) by 62%, an improved charging rate capability by ≈17% for 3C, an improved cycle stability by 26.5%, and charge throughput by 22.8%. For the check‐ups at C/10, improvements in cycle life and charge throughput of 51.1% and 42.4% are observed, respectively. The improved cycle life is due to the reduction of inhomogeneities in the jellyrolls as observed by X‐ray computed tomography. The data are put into context with cells from other studies to conclude the order of magnitude of the effects of tab design variation. Based on experimental findings, estimations are made for 46800 format cells regarding energy content and impedance.

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Section: Improvement Of Cycle Life By Foil Tab Designmentioning

confidence: 99%

Effects of Tab Design in 21700 Li‐Ion Cells: Improvements of Cell Impedance, Rate Capability, and Cycling Aging

et al. 2022

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Section: Introductionmentioning

confidence: 99%

“…Tabs are likely to cause inhomogeneities in the jellyroll [2,3], since they are usually thicker than the electrode coatings (single-sided coating thickness for anodes < 100 µm [4]). Such inhomogeneities can lead to deformations of the jellyroll after long-term cycling, especially at increased C-rates [2,3]. This should be different if the tabs were constructed from the current collecting foils themselves (Figure 1d), since they lead to less disturbed and therefore more homogeneous jellyrolls, which are closer to the mathematically ideal shape of an Archimedean spiral [5].…”

Section: Introductionmentioning

confidence: 99%

Increase of Cycling Stability in Pilot-Scale 21700 Format Li-Ion Cells by Foil Tab Design

et al. 2021

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Li-ion cells of the industrially-relevant 21700 format were built on pilot-scale with tabs made from (a) the electrodes’ current collecting foils (Al and Cu, “foil tabs”) in comparison with (b) conventional tabs (Al and Ni) welded to the electrodes’ current collecting foils (“welded tabs”). Both cell types use the same anode (graphite), cathode (NMC622), separator, electrolyte, as well as the same tab positions. This allows a direct comparison of welded tabs and foil tabs regarding formation, C-rate capability, cell electrical resistance, and long-term cycling stability tests. Our data reproducibly shows 14.4% longer cycling stability and 11.2% increased total charge throughput in the case of the cells with foil tabs until 80% SOH, which is likely due to less inhomogeneities in the case of the foil tab design.

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“…On the contrary, for positive electrodes the main forms of aging are structural changes, such as phase transitions or structural disordering, chemical decomposition, or metal dissolution. Furthermore, the loss of electrical contact between (i) the active material particles and (ii) the active material particles and the conductive additive causes an increase in resistance in both electrodes and therefore aging is promoted. − Among the positive electrode materials, LiMn 2 O 4 , LiNiO 2 , and LiCoO 2 transition-metal oxides have received increased attention; , however, to enhance specific capacity and thermal stability, research has been focused on LiNi x Mn y Co 1– x O 2 (NMC) layered oxides as positive electrode materials …”

Section: Introductionmentioning

confidence: 99%

Post-Mortem Analysis of Calendar-Aged 16 Ah NMC/Graphite Pouch Cells for EV Application

et al. 2017

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Application of Li-ion batteries for transportation not only requires long cycling life but also the preservation of the electrochemical performance during the resting period. For certain car usage this resting time could be predominant compared with the cycling activity and is referred to as calendar aging. To understand the aging mechanisms during calendar aging, an extensive post-mortem study was conducted on commercial 16 Ah NMC/graphite pouch cells stored at 5, 25, 45, and 60 °C. The post-mortem analyses were performed in parallel within three separate laboratories across Europe. They included visual inspection and structural and microstructural analysis along with a combination of analytical techniques to determine accurately the composition of positive (NMC) and negative (graphite) electrodes and the electrolyte. A direct correlation was established between the calendar-aging temperature and the degradation of the cells. The measurements revealed a severe deterioration phenomenon for the electrodes aged at 45 and 60 °C. These results are explained by the formation of a resistive interface on top of the negative electrodes due to a continuous and heterogeneous growth of a surface layer. Electrochemical impedance spectroscopy and electrochemical measurements confirm the resistance increase during cell degradation. At high temperatures, this occasionally leads to a Li deposition phenomenon. Nonetheless, we revealed that this degradation process does not affect the bulk structure of the materials but only the surface of the particles.

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An Explanation of the Ageing Mechanism of Li-Ion Batteries by Metallographic and Material Analysis

Cited by 16 publications

References 14 publications

Effects of Tab Design in 21700 Li‐Ion Cells: Improvements of Cell Impedance, Rate Capability, and Cycling Aging

Effects of Tab Design in 21700 Li‐Ion Cells: Improvements of Cell Impedance, Rate Capability, and Cycling Aging

Increase of Cycling Stability in Pilot-Scale 21700 Format Li-Ion Cells by Foil Tab Design

Post-Mortem Analysis of Calendar-Aged 16 Ah NMC/Graphite Pouch Cells for EV Application

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