The abrupt degradation of LiFePO4/graphite battery induced by electrode inhomogeneity

The abrupt degradation of lithium-ion battery (LIB) that seems to be normal in the early hundreds of cycles is a quite common phenomenon. Based on the LiFePO4/graphite battery, a series of methods are used to systematically analyze such a phenomenon that may bring reliability and safety risks to the LIB system. For differential voltage analysis, the shift of the characteristic peak can effectively reflect the lithium loss, which can be an early indicator to warn accelerating decay. The capacity of the cathode and anode can be restored almost completely by reassembling coin cells, proving that the electrode structure degradation is not the key factor for the abrupt failure. The X-ray photoelectron and Raman spectra only denote the different lithiation state rather than significant structural transformation after abrupt decay. The statistical data of coin cells of cathodes and Raman mapping of anodes show that the failed battery has worse compositional homogeneity at either macro or micro scale, which is the most likely mechanism for the abrupt decay. The presented results suggest that the electrode homogeneity is a key factor to make a battery system with robust cycle performance.