A quantitative method for early-stage detection of the internal-short-circuit in Lithium-ion battery pack under float-charging conditions

Detecting the internal short circuit (ISC) of Lithium-ion batteries is critically important for preventing thermal runaway. Conventional approaches mainly focus on ISC detection for dynamic load profiles, while the commonly seen float-charging scenarios with a high risk of ISC are rarely considered. Technical challenges arise from not only the lack of models describing battery dynamics at fully charged conditions but also the computational burden caused by the high number of series-connected cells in a battery pack. To address these issues, we here propose a simple and accurate method to quantitatively identify the leakage current of the battery with ISC, by checking the behaviors of the battery equalization system. Battery-in-the-loop experiments are carried out to verify the proposed method under a wide range of the short circuit resistances (similar to 20 to similar to 500 omega), using both LiFePO4 and Li(NiCoMn)0.33O2 batteries with different aging degrees. The typical errors of the identified leakage currents can be well-bounded within +/- 1 mA, including the cases of using both passive and active balancing. The proposed method is completely model-free and, therefore, can be transplanted into low-cost embedded systems to support broader applications.