Abstract:

Lithium batteries are widely used in new energy electric vehicles and energy storage because of their superior performance. However, micro-short circuits in lithium batteries are a safety hazard during the use of battery packs. This paper proposes a method to diagnose micro-short circuits on the basis of the change in the relative charging time of the cell to determine whether the battery pack is micro-short and judge the micro-short circuit cell. At the end of the battery pack charging, this method uses the voltage curve of the cell that first reaches the charge cut-off voltage as a reference, analyzes the charging times for other cells to reach the charge cut-off voltage under the condition that they can continue to be charged, and characterizes these with the relative charging time. Because of the micro-short circuit battery's continuous consumption of electrical energy, its relative charging time increases with the number of charging times. Accordingly, each cell's relative charging time in the battery pack is analyzed, and abnormality detection is performed through the box diagram. Among the abnormal monomers detected, the micro-short circuit cell has the most repeated occurrences. While analyzing the relative charging time, analyzing the influence of the DC internal resistance on the diagnosis result is necessary to improve the result's accuracy. After a comparative analysis, the diagnosis results are highly consistent with the actual results. The implementation of this method does not require special tests on the battery pack; the operation is convenient, which can guide battery pack safety testing.

Key words: battery pack, micro short circuit, relative charging time, box diagram