Wide range of malfunctions can occur during the operation of lithium-ion battery packs (BPs). However, most existing studies focus on internal short circuits and thermal runaway of the battery detection. The same statement also applies to the most common monitoring methods of BP operating parameters and their faults detection. Therefore, such methods may be incapable of identifying a malfunction such as degradation or a complete loss of electrical connection to a cell within the battery. At the same time, losing a connection to even a single cell in the BP can lead to significant changes in operating modes, affecting the overall safety, efficiency, and longevity of the battery. Modeling this type of failure is an essential step in developing new and more effective diagnostic methods for BPs. This study models a 3s7p battery pack consisting of lithium-ion 18650 cells with a lost connection to one of the cells. Numerical modelling is conducted utilizing COMSOL Multiphysics software. A mathematical model of the thermoelectric processes in the battery is described. The finite element method is used to calculate the thermal field during battery discharge. The impact of the lost cell on neighbouring cells and the overall BP is examined. The modeling results confirm that the loss of a cell creates an imbalance in current distribution among the battery cells, leading to accelerated heating and rapid discharge of the cells connected in parallel with the lost one. Although the remaining cells discharged more slowly, they cannot compensate for the overall loss of battery state of charge. These changes increase the risk of overheating the functional cells and may contribute to their rapid degradation in the future. The thermal field inside the battery is calculated. Its analysis shows distinct differences when compared to a healthy battery. The results may be useful for further development of improved BP design and thermal management methods. The recommended method can be utilized for diagnostics and early fault detection in lithium-ion battery packs, thereby decreasing operational risks and enhancing battery longevity.
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