The often-observed current distribution between parallel-connected lithium-ion cells within battery modules is probably evoked by the properties of the connection, inhomogeneous contact and power line resistances, the impedance behavior of single cells and of the DoD. The extent to which each of the contributors and the interaction between them affects the current distribution within the battery module is crucial to improve the system’s efficiency, which is investigated here via various electrically cross-linked, physicochemical-thermal simulations with variable system terminal (ST). Consequently, cross-connectors balance the system and reduce DoD shifts between cells. Furthermore, if one compares ST-side and ST-cross, the position of the ST is negligible for topologies that incorporate at least two cells in serial and parallel. Depending on the ST configuration, point and axis symmetry patterns appear for the current distribution. Compared to welding seam and cross-connector resistances, the string connector resistance dominates the current distribution. Like the behavior of a single cell, the system’s rate capability shows a non-linear decrease with increasing C-rate under constant current discharge. As a recommendation for the assembly of battery modules using multiple lithium-ion cells, the position of the ST is of minor importance compared to the presence of cross-connectors and low-resistance string connectors.

Aging behavior and long-term cell-to-cell variations have been much more frequently investigated in single-cells than cells connected in parallel. In particular, the literature lacks a study investigating the aging behavior of cells in parallel that is based on defined cell-to-cell variations and on the results of a previous single-cell aging study. Moreover, present studies are unable to exclude the impacts of measurement systems on their final results. To counter this deficiency, a novel 4-wire measurement technique is used which does not influence the current distribution but allows both single and parallel measurements to be recorded without changing the measurement configuration. Cells in parallel generally displayed improved aging behaviors in comparison to those seen in the single-cell aging study and the positive influence of extended CV-charging was evident, as long as the CV-charging phase was limited in length. It was also observed that the exclusion of critical voltage ranges exerted the most significant influence on the aging rate and dominates the influence of initial cell-to-cell variations in the long-term. As a result, it is recommended that module manufacturers reduce the effort spent on initial cell matching strategies for cells in parallel in favor of developing cell-specific charging profiles.

This study presents a method to analyze the electrical resistance of planar contacts. The method can determine whether the contact resistance of the joint exhibits linear or non-linear behavior. By analyzing the current distribution over a planar contact, it can be determined whether an area-based contact resistance is justified or if other parameters define the contact resistance. Additionally, a quantitative evaluation of the factors that affect the measurement accuracy, including the positioning, the measurement equipment used, and the influence of the current injection on the sense pin was conducted. Based on these findings, the electrical contact resistance and the mechanical ultimate tensile force of a silver-filled epoxy-based adhesive are analyzed and discussed. The layer thickness and the lap joint length were varied. Overall, the investigated adhesive shows a low contact resistance and high mechanical strength of the same magnitude as that of well-established joining techniques, such as welding, press connections, and soldering. In addition to evaluating the mechanical and electrical properties, the electric conductive adhesive underwent an economic assessment. This analysis revealed that the material costs of the adhesive significantly contribute to the overall connection costs. Consequently, the effective costs in mass production are higher than those associated with laser beam welding.