Thermally and electrochemically driven imbalances might reduce the overall net energy within large format lithium-ion batteries. In this study, we designed a proprietary multi-tab pouch cell for investigation of these imbalances depending on cell design and temperature. The cell consists of a single-layered NMC/graphite electrode pair with a length of 50 cm and a width of 10 cm. 22 equidistantly distributed tabs are connected to each electrode giving insight to local potentials within the current collector domain (Fig. 1). Temperature variation is negligible due to the comparably small heat generation of the cell and the global influence of temperature can be analyzed. A high precision measurement setup is prepared for a μV resolution between tab pairs. By that, the internal current density distribution can be assessed.

The cell is operated at 5, 25 and 40 °C and 0.1, 0.5, 1 and 2C current rate, whereby three different tab patterns are applied: Standard pouch cell, counter-tab and center-tab design. It turns out that higher potential drops along the cell as well as larger potential variation occur at elevated temperature. Further, the differentiation of potential difference between the tabs indicates a larger state of charge inhomogeneity at higher temperature, even at low current rates. It might be concluded that the interaction of an increased current collector resistance and an increased electrochemical performance in between the collector foils provokes a more distinct inhomogeneity in current density at higher temperature.

Corresponding to our previous work [1,2], we apply a multi-dimensional modeling approach to the presented multi-tab cell to describe the temperature dependent current spread for purpose of optimized cell design. Based on these simulations, a maximum tab-to-tab distance depending on temperature can be estimated under the objective of an acceptable potential drop along the current collectors.

References:

[1] P.J. Osswald, S.V. Erhard, J. Wilhelm, H.E. Hoster and A. Jossen: Simulation and Measurement of Local Potentials of Modified Commercial Cylindrical Cells - Part I: Cell Preparation and Measurements, Journal of The Electrochemical Society 162 (10), A2099, 2015

[2] S.V. Erhard, P.J. Osswald, J. Wilhelm, A. Rheinfeld, S. Kosch and A. Jossen: Simulation and Measurement of Local Potentials of Modified Commercial Cylindrical Cells - Part II: Multi-Dimensional Modeling and Validation, Journal of The Electrochemical Society 162 (14), A2707, 2015