| Lithium-ion batteries are widely used in portable devices, household electronics, and transportation vehicles. Accurately estimating the state of charge (SOC), state of health (SOH), and remaining usable lifetime (RUL) of Li-ion batteries is increasingly important. New diagnostic method are needed to improve battery management and performance. Here we review electrochemical impedance spectroscopy (EIS) based SOC and SOH estimation methods. We then introduce a new method to do EIS on portable devices. We show that screen brightness modulations can be used to produce a modulated current at the battery. The modulated current induces a modulated voltage signal. Fast Fourier Transforms (FFTs) of the current and voltage signals are used to determine the battery impedance at the modulation frequency. An Android application is used to control the screen modulation and make the current and voltage measurements on the phone. The prototype EIS application is demonstrated as a potentially valuable new characterization tool for on-device battery diagnostics. |
