Influence of connection impedance on the performance of parallel-connected lithium-ion battery modules

Abstract

Parallel lithium-ion battery modules are crucial for boosting the energy and power of battery systems. However, the presence of faulty electrical contact points (FECPs) between the cells often leads to severe performance degradation, including reduced capacity, accelerated aging, and the potential risk of thermal runaway. Hence, comprehending the influence of connection impedance (CI) on battery module performance and effectively diagnosing FECPs in parallel modules are of paramount importance for ensuring the secure and efficient operation of battery modules. This study investigates the influence of CI within a LiFePO4/graphite 2-parallel module, focusing on voltage, capacity, temperature, and electrochemical impedance spectroscopy (EIS). The findings reveal a direct relationship between increased CI and decreased capacity as well as diminished rate capability of the battery modules. Moreover, the presence of FECPs induces voltage fluctuations between cells and modules, while concurrently accelerating the rate of temperature elevation at the FECPs. Through EIS analysis, this study identifies the connection quality and locates FECPs within the 2-parallel module. The insights gained from this research offer valuable guidance for optimizing the design and performance of parallel-connected lithium-ion battery modules, ultimately enhancing the efficiency and reliability of energy storage systems.