Aging Monitoring Method for Lithium-Ion Batteries Using Harmonic Analysis

Monitoring the aging battery cells is important to maintain battery performance. Capacity is a key indicator of battery aging diagnosis, but capacity can be estimated differently depending on the C-rate. Battery impedance monitoring using electrochemical impedance spectroscopy (EIS) is also recognized as a battery diagnostic method. However, EIS is inefficient when diagnosing a large number of individual battery cells due to complex computation and measurement time. In this article, a harmonic analysis method for monitoring aging battery is proposed. The proposed diagnostic technique applies the designed 1-kHz sinusoidal signal, comprising a sinusoidal current component and a direct current component, to the battery. Harmonics are generated when signals passing through nonlinear systems are distorted. A battery is an asymmetric nonlinear system with different bidirectionality. Comparing the simulation and experimental results, we confirmed that the harmonic signatures are the indicators that distinguish between a normal and an aging battery. Moreover, the proposed in situ technique can be applied during charge/discharge cycles, even in the case of an apparent reduction of even harmonics.