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Assessment of different Fast Charging Strategies for Cycling Lithium-Ion Batteries
Poster Exhibition
Life cycle analysis (LCA)

Fast charging is one of the main challenges of lithium-ion batteries as it may increase the cell degradation. The most important degradation effect associated with fast charging is called lithium-plating. If the negative electrode’s (anode) voltage drops below 0 V vs. lithium during charging, metallic lithium is likely to arise on the anode’s surface. This lithium-plating leads to capacity fade and may lead to undesired side reactions or an internal short circuit in the worst case as the lithium-plating is likely to occur as sharp dendrites. These consequences benefit an earlier cell defect, resulting in a reduced cyclability and shorter life time.
In this contribution different fast charging strategies are tested. On the one hand, there is a state of the art 3C constant-current-constant-voltage (CCCV) strategy that lasts about 20 min for 0 – 80% SOC for the considered NMC622/G cells. On the other hand, there is a model-based optimized fast charging strategy by minimizing the anode´s voltage to a low positive value in order to prevent lithium-plating. The electrode equivalent circuit model (EECM) is parameterized by 3-electrode-cells and a novel parameterization approach. The model shows good simulation fidelity of about <20mV root mean square error between 0 – 100% SOC for 0.05C – 3C currents. Based on the model, the fast charging current is maximized considering an anodic voltage boundary of 10mV. By limiting the maximum current to 3C, the fast charging time is about 30min for 0 – 80% SOC. The state of the art 3C CCCV and the optimized 3C strategy are used for the cycling of the cells. It is found that the state of the art 3C CCCV strategy leads to huge degradation related to lithium-plating as proven by optical post-mortem-analysis after 100 cycles. In contrast, the optimized strategy prevents lithium-plating even after 300 fast charging cycles and shows a significant lower degradation as the state of the art 3C CCCV method. The results present a successful validation of the model-based approach. The method can be used in order to design optimized fast charging strategies that prevent lithium-plating. This will lead to a short charging time while guaranteeing a longer cycle life compared to common CCCV methods. Moreover, time-consuming aging studies can be accelerated while preventing lithium-plating.

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Prof. Dr.-Ing. Kurrat