A fast diagnosis method for accelerated degradation fault induced by overcharging of LiFePO4 batteries

The second-use application technique is an effective method to deal with the retired batteries from electric vehicles, which avoids energy waste and reduce vehicle cost. Since the accelerated degradation fault results in the fast degradation of the battery performance, especially under the storage condition, it is urgently to be diagnosed before the second-use application. A fast diagnostic method is developed for the accelerated degradation fault with the following contributions. First, the unusual changes in the charging voltage that approach the upper limit (Back-end voltage) caused by accelerated degradation fault is detected. By the mechanism analysis, it is revealed that the correspondence between the unusual Back-end voltage variation and fault mechanism is deterministic. Second, according to the particular Back-end voltage variation, a novel fault feature (κ) is proposed. Furthermore, to calculate κ reliably, how to acquire the Back-end voltage is determined based on the full-voltage composition; the third-order spline least-square method is utilized to smooth the Back-end voltage data. Finally, the proposed diagnostic method for accelerated degradation fault is validated via the large number of retired batteries, which guarantees that even if the historical driving data is lost, the accelerated degradation fault can be effectively diagnosed with better accuracy.