In Situ Inversion of Lithium-Ion Battery Pack Unbalanced Current for Inconsistency Detection Using Magnetic Field Imaging

The performance inconsistency of lithium-ion battery packs is one of the key factors that lead to their accelerated lifespan degradation and reduced reliability. Hence, it is of great significance to accurately detect the consistency of cell parameters within the pack without destructive testing. The working current of the cell is the most direct and effective parameter to characterize the consistency of its module. However, cell-level current is not monitored in commercial battery packs due to the limitations of current sensors. Therefore, this work proposes an inversion method using in situ magnetic field imaging for detecting unbalanced current induced by performance inconsistency of the pack. Through elucidating the superposition property of current-induced magnetic field (CIMF) between cells, a current inversion model (CIM) for the battery pack is constructed, with the model principle and solution method given. Battery packs with different configuration structures are designed, simulated, and measured. The results show that this method can reduce the interference of susceptibility-induced magnetic field (SIMF) and achieve milliampere-level current calculated accuracy. This provides a new way to quickly and accurately evaluate the performance consistency of battery packs and provides a technical guarantee for battery pack service performance testing and maintenance.