Browsing by Author "Schaltz, Erik"
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Item Open Access Self-balancing feature of Lithium-Sulfur batteries(Elsevier, 2017-11-05) Knap, Vaclav; Stroe, Daniel-Ioan; Christensen, Andreas E.; Propp, Karsten; Fotouhi, Abbas; Auger, Daniel J.; Schaltz, Erik; Teodorescu, RemusThe Li-S batteries are a prospective battery technology, which despite to its currently remaining drawbacks offers useable performance and interesting features. The polysulfide shuttle mechanism, a characteristic phenomenon for the Li-S batteries, causes a significant self-discharge at higher state-of-charge (SOC) levels, which leads to the energy dissipation of cells with higher charge. In an operation of series-connected Li-S cells, the shuttle mechanism results into a self-balancing effect which is studied here. A model for prediction of the self-balancing effect is proposed in this work and it is validated by experiments. Our results confirm the self-balancing feature of Li-S cells and illustrate their dependence on various conditions such as temperature, charging limits and idling time at high SOC.Item Open Access A self-discharge model of Lithium-Sulfur batteries based on direct shuttle current measurement(Elsevier, 2016-10-29) Knap, Vaclav; Stroe, Daniel-Ioan; Swierczynski, Maciej; Purkayastha, Rajlakshmi; Propp, Karsten; Teodorescu, Remus; Schaltz, ErikIn the group of post Lithium-ion batteries, Lithium-Sulfur (Li-S) batteries attract a high interest due to their high theoretical limits of the specific capacity of 1672 Ah kg−1 and specific energy of around 2600 Wh kg−1. However, they suffer from polysulfide shuttle, a specific phenomenon of this chemistry, which causes fast capacity fade, low coulombic efficiency, and high self-discharge. The high self-discharge of Li-S batteries is observed in the range of minutes to hours, especially at a high state of charge levels, and makes their use in practical applications and testing a challenging process. A simple but comprehensive mathematical model of the Li-S battery cell self-discharge based on the shuttle current was developed and is presented. The shuttle current values for the model parameterization were obtained from the direct shuttle current measurements. Furthermore, the battery cell depth-of-discharge values were recomputed in order to account for the influence of the self-discharge and provide a higher accuracy of the model. Finally, the derived model was successfully validated against laboratory experiments at various conditions.Item Open Access Significance of the capacity recovery effect in pouch lithium-sulfur battery cells(The Electrochemical Society, 2016-12-07) Knap, Vaclav; Zhang, Teng; Stroe, Daniel-Ioan; Schaltz, Erik; Teodorescu, Remus; Propp, KarstenLithium-Sulfur (Li-S) batteries are an emerging energy storage technology, which is technically-attractive due to its high theoretical limits; practically, it is expected that Li-S batteries will result into lighter energy storage devices with higher capacities than traditional Lithium-ion batteries. One of the actual disadvantages for this technology is the highly pronounced rate capacity effect, which reduces the available capacity to be discharged when high currents are used. This drawback might be addressed by the use of the capacity recovery effect, which by introducing relaxation periods between consecutive pulse discharges of the battery, increases the available discharge capacity of the cell. The capacity recovery effect of the Li-S cell is studied in this paper using the pulse discharge technique, considering its dependence on the applied current, discharge step length, temperature, and on the length of the relaxation period between the discharging pulses.