**5. Conclusions**

In this article a test bench was presented, which enables the individual temperature control of each cell connected in parallel. This allows to reconstruct arising temperature gradients in a battery module due and to investigate their impacts on the dynamic of the current distribution. The aluminum plates adjacent to the cells can be heated and cooled with a rate of about *T* ˙ Plate = 250 mK·s<sup>−</sup>1, which exceeds the maximum heating rate of the cells due to dissipation with *T* ˙ Cell = 114 mK·s<sup>−</sup>1. The influence of the test bench on the current distribution caused by induced additional resistors was determined and minimized. The contact resistance at the cathode tab was reduced from *R*Tab+ = 81.18 μΩ to *R*Tab+ = 55.15 μΩ by treating with a non-woven abrasive cloth, cleaning with an oxide-dissolving spray and increasing the pressure from *p* = 27 N · mm<sup>−</sup><sup>2</sup> to *p* = 93 N · mm<sup>−</sup>2. In addition, an increase of the contact resistance during the test period is prevented by air seal of the contact. Without air sealing, the resistance increased from *R*Tab+ = 57.54 μΩ to *R*Tab+ = 133.57 μΩ within 51 days at room temperature. The contact resistance at the anode tab was reduced by the same treatments from *R*Tab−= 35.59 μΩ to *R*Tab−= 28.2 μΩ. Due to their nickel coating an air seal was not necessary.

Measurements of two parallel-connected cells with load cable resistances of *R*Cab+ = 0.3 <sup>m</sup>Ω, *R*Cab+ = 1.6 mΩ and *R*Cab+ = 4.35 mΩ showed qualitatively the same dynamic of the current distribution with decreasing current differences within the parallel-connected cells with decreasing cable resistance. An ECM considering the current distribution within the cells as well as the impacts of the induced resistances by the test bench was introduced, parameterized and compared to measurements. The model fitted well to measurements with an RMSD of *ξ*RMSD = 0.083 A. Measurements simulating different cell positions in a battery and thermal connections of cells to their neighbor cells were conducted. The consideration of a cell at the module edge showed increasing temperature differences of Δ*T* = 3.8 ◦C for thermal-coupled cells and of Δ*T* = 15.8 for thermal isolated cells. This temperature difference further increased the initial cell parameter difference and led to higher current and SoC gaps within the parallel-connected cells. The crossing point of the cell current was delayed with increasing Δ*T*, which in turn caused an increasing current peak of cell two from *I*2 = 0.73 · *I*Batt to *I*2 = 0.81 · *I*Batt comparing the thermal-coupled and isolated scenarios.

**Author Contributions:** A.F., T.M., T.S. and R.L. conceived and designed the test bench. A.F., T.M. and T.S. conducted the experiments and analyzed the data. A.F. designed the simulations and wrote the article. K.P.B. and T.S. contributed to the manuscript design and revised the article. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors want to thank Björn Mulder for reviewing the article.

**Conflicts of Interest:** The authors declare no conflict of interest.
