Influence of Cell-to-Cell Variations on the Inhomogeneity of Lithium-Ion Battery Modules

Abstract

Inhomogeneity within lithium-ion battery modules can occur due to variations in capacity and impedance of the connected cells as well as due to thermal gradients or cell connector design. We present a model for describing xSyP battery modules during operation, which is able to study these effects. The multidimensional multiphysics model includes a physicochemical model describing the electrochemical behavior of each cell. The electrical model accounts for the conservation of electric charge and energy between the cells to reach electrical consistency according to the respective module topology and cell interconnections. The model is capable of investigating the influence of defective and asymmetric cell connectors on the inhomogeneity of module operation. To evaluate this electrical influence, the observed inhomogeneities are compared to the influence of thermal gradients between the cells. The resulting inhomogeneous current distribution is presented for a module of two parallel connected lithium iron phosphate-graphite cells under constant current discharge operation for variations in cell capacity, cell impedance and ambient temperature at different module contact scenarios. From the observed impact of both, electrical and thermal variations between parallel connected cells, a matching strategy is derived and discussed which can enhance a module's performance during e.g. second life applications.

Measurement of the Temperature Influence on the Current Distribution in Lithium‐Ion Batteries

“…Regarding temperature, there are both simulative [ 26–28 ] and experimental [ 27–29 ] investigations on its influence on the current distribution in parallel connected cells. The studies differ in terms of cell chemistry, number of cells, temperature differences, and temperature level, however, they achieve similar conclusions.…”

“…[ 27 ] Thus, the current distribution is also influenced by the shape of the OCV‐versus‐SOC‐function and the changes in its gradient, which affect the profiles of the individual cell currents. [ 26,29,31,32 ] In addition, after terminating charge or discharge processes, charge compensation between the cells takes place, [ 33,34 ] so that the differences in the OCV as a function of the SOC are neutralized. [ 35 ] Furthermore, the C‐rate has an influence on the individual cell currents.…”

Numerical study on sensitivity analysis of factors influencing liquid cooling with double cold‐plate for lithium‐ion pouch cell

“…The life span of a lithium‐ion battery is influenced by the operating conditions, including temperature 10 . The Arrhenius equation suggests the exponential dependence of the reaction rate on temperature 11 . The non‐uniform temperature distribution affects the performance of a lithium‐ion battery 12 .…”

Degradation and Dependence Analysis of a Lithium-Ion Battery Pack in the Unbalanced State

“…The unbalanced state refers to a situation in which the high level of non-uniformed operational states of the components would speed up the failure process of an entire system [4]. As a typical performance balancing system, the consistency of lithium-ion packs has always been a matter of concern [5][6][7][8]. Due to manufacturing tolerances and environmental stresses during use, there are typically performance differences between individual cells [9].…”