Fractional-order equivalent circuit model for commercial sodium-ion batteries in a wide temperature range considering aging

Abstract

With the development of electric vehicles and microgrids, the demand for energy storage is growing rapidly. Sodium-ion batteries, due to their abundant reserves, high energy density, and good safety, are beginning to be used in electric vehicles and energy storage power stations. High-precision modeling is the basis for state estimation and energy management of sodium-ion batteries. Fractional-order equivalent circuit model is favored for its balance between computational complexity and accuracy. In this study, electrochemical impedance spectroscopy tests were conducted on sodium-ion batteries, and a fractional-order equivalent circuit model in a wide temperature range considering aging, was established. The model parameters can be identified online using the global optimization algorithm based on dynamic cycling condition. The model’s accuracy was verified under different temperatures and dynamic working conditions. The results show that, compared to the Thevenin model and second-order equivalent circuit model, the fractional-order equivalent circuit model can better fit the terminal voltage of sodium-ion batteries, with a mean relative error of less than 4%.