Novel equivalent circuit model for high-energy lithium-ion batteries considering the effect of nonlinear solid-phase diffusion

Abstract

Efficient and accurate management of lithium-ion batteries (LIBs) highly relies on models that capture the in-cell nonlinear behaviors. As one of the most dominant dynamics inside high-energy LIBs, the solid-phase diffusion shows nonlinearity because the lithium diffusivity in solid phase is a physical parameter varying with the lithium concentration. Yet, this nonlinearity has not been well disclosed in the electrical modeling field of LIBs. This paper presents a novel equivalent circuit model in which the effect of nonlinear solid-phase diffusion is considered. First, the modeling process is illustrated, and it is worth noting that the circuit representation of solid-phase diffusion is established based on its physical principles at electrode particle level. Second, while paying special attention to the relaxation voltage offset, the model parameters are identified with the help of the multi-timescale characteristics of batteries during the voltage recovery period in pulse discharge test. Finally, the model is thoroughly validated by performing constant-current discharge and dynamic tests on the commercial high-energy LIBs. Results show that the proposed model remains robust to the state-of-health of batteries and outperforms the conventional second-order resistor–capacitor model. Moreover, the model keeps similar simplicity to the conventional one and can meet the real-time requirements in engineering.