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Poster-No.

P4-003

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Fast charging of lithium-ion batteries and range of electric cars are decisive criterions for the acceptance of electromobility in society. The requirements for fast charging differ depending on the application, which is often limited by the material system and cell design. In the aging process, the cell properties degrade, which can be accelerated by fast charging cycles. Therefore, the operating limits are often configured pessimistically, in order to avoid accelerated aging effects and safety-critical processes. Another possibility is to determine the aging-dependent operating limits and to adapt the charging strategy accordingly. Three-electrode cell setups enable to measure the positive and negative electrode voltage severally, so that electrical equivalent circuit models (EECM) can be parameterized for each electrode separately. Consequently, fast charging profiles can be simulated by pretending a minimum anode voltage. The safety-critical deposition of metallic lithium (lithium-plating) occurs with a negative anode voltage and can lead to irreversible loss of lithium ions. Scaling up the simulated charging strategy based on three-electrode cells to larger pouch cell formats poses a challenge. The stainless steel plunger used in the three-electrode cell setup have such large heat capacities that constant temperatures in cells are expected during the charging process. In the pouch cell format can be noticed a variation of temperature along two dimensions (length and breadth) which leads to higher ohmic resistances in colder areas of the cell. In these areas, the probability of lithium-plating increases. Silicon-graphite electrodes enable higher energy densities than pure graphite electrodes, which promises greater ranges in electromobility. In this study, fast-charging strategies for lithium-ion-cells with silicon-graphite-anodes are model based derived and tested on three-electrode cells and pouch-cells. The study shows the cycling and post-mortem results in addition to challenges of the upscaling from laboratory cell formats to bigger cell formats.