Discrete-time modeling of Li-ion batteries with electrochemical overpotentials including diffusion

Abstract

A battery equivalent circuit model (ECM) is proposed using a novel physics-based diffusion component and N resistor–capacitor (RC) pairs, hence its name the ‘DNRC model’. The DNRC model characterizes ohmic, charge transfer, and diffusion overpotentials in the time domain with physically-meaningful circuit elements. Unlike the Warburg impedance, the diffusion component has no need for frequency-domain data and is formulated entirely in the time domain. Physical interpretability is validated by comparison with physics-based model (PBM) generated data. Experimental validation is performed at a wide range of state of charge (SoC) and state of health (SoH) using pulse injection and drive cycle data. The mean absolute percent error is below 0.3% using 5 circuit elements for 4 min of an arbitrary current load. The DNRC model is grounded in physical principles, suitable for real-time estimation, and may form the basis for new approaches to degradation reduction or diagnosis in battery management systems.