Throughout the project an extended electrical characterization has been performed on silicon based non-commercial pouch cells. One important conclusion is that effect of mechanical pressure on this cell has a significant influence on its performance: mainly capacity retention (ultimately cycle life) and energy density. In this paper this influence will be discussed in detail by using classical electrical characterization tests such as an Open-Circuit Voltage test (OCV), a capacity test and Hybrid Pulse Power Characterization (HPPC) test complying with the existing standards. In this abstract only the capacity test will be discussed, the remaining tests will be discussed in the full paper.
Results and discussion:
The procedure used during the capacity test consists of standard charging phase (constant current and constant voltage) followed by several discharges at different C-rates (C/5, C/3, 1C & 1.5C), based upon the international standard IEC 62660-1. The current and its corresponding voltage response of a capacity test of the clamped Si-alloy pouch cells is visualized in figure 1. Figure 2 provides a comparison of the discharge capacity of both the clamped an unclamped pouch cells. It can be clearly seen that when clamping the cell a significant increase of 10-20% in the discharge capacity can be observed. The most probable root cause of this difference is due to gassing of the negative electrodes because after the electrical characterization tests it can be clearly observed that the unclamped pouch cells are swollen and the clamped ones show no signs of swelling. These gasses are not conductive resulting in regions of low conductivity which are not taking part anymore in the electrochemical reactions. The clamped cell shows no swelling which can be explained by two reasons: firstly, it is possible that due to the pressure of clamping the gassing is reduced or secondly that the gas is pushed to the side of the cell where it doesn’t interfere with the electrochemical reactions. Since no gassing is observed the firstly is more likely.
An extended analysis of the effect of mechanical pressure on the electrical performance will be discussed in detail in the full paper by means of the remaining electrical characterization tests (OCV and HPPC) as well as an extended investigation of the root cause will be discussed in the full paper.
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This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 653531. Further, we acknowledge the support to our research team from “Flanders Make”.