Interpretable Real-Time Modeling of the Diffusion Overpotential in Lithium Batteries

Fractional-order dynamics can form physically interpretable equivalent-circuit models (ECMs) of the diffusion overpotential in lithium-ion batteries (LIBs) but have complex formulations in the time domain. Meanwhile, resistor-capacitor circuits have simple implementations but little physical meaning. Thus, we propose a discrete-time state-space diffusion model, named "receding-horizon diffusion" (RHD). It combines physical interpretability with computational simplicity. Analogous to the Warburg element in impedance spectroscopy, the RHD constant is explicitly linked with the lithium-ion diffusion coefficient. Fivefold validation of the RHD model using simulated and experimental from lithium NiMnCo and NiCoAl cells up to 3 C-rate, temperatures from 0 degrees C to 25 degrees C, and wide ranges of states of health and charge. The model has less than 1% modeling error. Ohmic, charge-transfer, and diffusion overpotentials are tracked in real time. The RHD model could be integrated into battery management systems (BMSs) in electric vehicles (EVs) and used in standard state estimation techniques.