Performance of LiFePO4 batteries in parallel based on connection topology

Abstract

Connection topology directly affects the performance of a battery pack, which must satisfy the demand of all-weather environments and the complex operating conditions of electric vehicles. Currently, studies focus on battery state estimation and inconsistency reduction to obtain high energy efficiency and long lifetimes, while lacking a comprehensive analysis of the battery inconsistency generation mechanism. Here, a method based on the battery posts position and connector resistance is developed to explain how connection topology affects the performance of LiFePO4/graphite batteries in parallel by experiments and theoretical analysis. Quantitative analyses of the interactions between current distribution and battery internal resistance, battery internal resistance and connector resistance, as well as load current rate and battery self-equalization, are discussed. The results indicate that the asynchronous change of individual cell voltage causes the voltage fluctuation of the battery module. The battery module has a larger available capacity at small current rates than at large ones. However, over-charge and over-discharge of individual cells are more likely to occur. Therefore, the cut-off conditions should be adjusted according to load current rates. Research on battery connection topology can directly contribute to better performance of the battery module, and improve the efficiency, reliability and economy of electric vehicles.