(Invited) Lithium Plating as a Critical Ageing Mechanism in Lithium-Ion Batteries – Detection by Advanced Methods and Mitigation
Authors: Waldmann Thomas , Hogrefe Christin , Fluegel Marius , Feinauer Max , Kasper Michael , Wohlfahrt-Mehrens Margret 
Published: February 2024

The cycle life of Li-ion batteries is limited by aging on the material and electrode level. Prolonging the battery life helps increasing sustainability, reducing the dependency from critical raw materials, and safes costs. The first step in extending battery life is to understand the underlying degradation mechanisms. Post-Mortem analysis of commercial and pilot-line made cells showed that Lithium plating is a very relevant and severe aging mechanism which can lead to high aging rates and decrease safety properties.1 In this talk, we analyse the aging mechanism of Lithium plating on cell and electrode level.
On cell level, capacity fade per time yields aging rates, which are temperature dependent. This temperature dependency is analyzed via Arrhenius plots. The Arrhenius plots for cycling aging show a typical V-shape with a low and a high temperature branch.2–4 A minimum in the Arrhenius plot corresponds to the maximum cycle life of the battery, while the low temperature branch indicates Lithium plating. Interestingly, the minimum in the Arrhenius plot shifts with the charging C-rate, the battery type,3,4 and – in case of non-linear capacity fade curves – with aging.4

In the last years, our group developed new semi-quantitative methods based on glow discharge optical emission spectroscopy (GD-OES) depth profiling for detection of Lithium plating on graphite5 and on Si/graphite composite anodes.6 Furthermore, a new in situ optical microscopy method with cross-sectioned full cells allows direct observations of the electrodes during charging and discharging.7,8 The color change of lithiated graphite in combination with simultaneous electrochemical data gives insight into the charging behavior of anodes. Under slow charging conditions (0.1C), the lithiation of the anode is observed to be homogeneously. Most interestingly, at 1C transport limitations come into play and lithiation fronts moving from the anode surface to the current collector can be directly observed and quantified by image analysis. Our results of both methods5,6,8 and in full consistence with simulations by others9 show that Lithium is mainly deposited on the anode surface, i.e. near the separator (see Figure).
Finally, we show that Lithium deposition can be prevented by avoiding anode potentials < 0 V vs. Li/Li+ in commercial cells and cells from our pilot-line. Interestingly, Si/graphite anodes in pouch full cells show a lower susceptibility to Lithium plating at low temperatures with increasing Si content and the same anode areal capacity and N/P ratio. This suggests that the transport limitations in the pores of these Si/graphite anodes are reduced due to lower anode coating thickness.

References

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M. Flügel, K. Richter, M. Wohlfahrt-Mehrens, and T. Waldmann, J. Electrochem. Soc., 169, 050533 (2022).

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Acknowledgement

The authors would like to acknowledge the Federal Ministry for Economic Affairs and Climate Action (BMWK) for financial support of the Structur.e project (03ETE018E), the German Federal Ministry of Education and Research (BMBF) for funding of the project CharLiSiKo (03XP0333A) and the TEESMAT project (Horizon 2020 E.U. Framework Program, Grant Agreement N° 814106, http://www.teesmat.eu).

Figure 1