Impedance Measurement of Lithium-Ion Batteries Using Optimized Pulse Patterns

Abstract

As the demand for Lithium-ion (Li-ion) batteries has surged in recent years, concerns about their environmental impact have grown. Instead of disposing of these batteries in landfills at the end of their lifecycle, interest in recycling cells for second-life applications has increased. A key factor in assessing the reusability of these cells is determining their state of health (SOH). Battery internal impedance, which is closely tied to SOH, serves as a reliable and rapid indicator of a battery’s health status. Recent studies have introduced fast and easily implementable impedance measurement methods based on broadband excitations and Fourier techniques. These methods involve subjecting the battery under test to charge and discharge cycles according to the excitation signal. The resulting voltage and current waveforms are measured, and impedance information is extracted via the Fourier transform. While effective, many broadband excitations are designed as discrete-time sequences, which restrict and limit signal properties in practical applications. This paper proposes a continuous-time excitation design method based on optimized pulse patterns (OPP). The OPP approach identifies optimal time instants for a predefined number of signal level changes within a signal period. Compared to discrete-time signal designs, the OPP method offers several significant advantages. It allows unrestricted signal generation frequencies and can be optimized for any injection device. Additionally, the spectrum shape of the OPP excitation can be largely controlled, enabling maximized perturbation energy at desired frequencies. Experimental measurements using broadband excitations designed with the proposed OPP method demonstrate the effectiveness of this approach.