Effect of cell-to-cell variation and module configuration on the performance of lithium-ion battery systems

The performance of lithium-ion battery modules significantly depends on cell-to-cell variations and connection topology. In particular, inhomogeneous distribution across the parallel battery module results in performance degradation and potential safety problems. This study evaluates the overall performance of battery modules, including parallel-connected cell groups with different system terminal positions, and examines the effect of cross-connectors. First, a battery module model with electrochemical, thermal, and aging properties is introduced. An LMN structure that allows all battery module structures was proposed for the first time. Next, modules with different topologies are simulated to analyze the cell-to-cell variations in terms of current, temperature, and aging. Finally, six performance indices are extracted from the simulation results to represent the module performance. The module with the cross-contacting system terminal reduces the effect of the connection resistance on the cell-to-cell variation, showing clear improvement over other topologies of up to 61.5%. Additionally, the use of cross-connectors reduces inconsistencies between cells and improves the safety of the battery modules in the event of potential problems. The number of cycles increases by over four times compared with the general case and no significant overdischarge state is observed in a particular cell. The proposed method can be used to solve system-level problems and assist engineers in designing battery management systems to provide longer-lasting and more efficient energy storage systems.