Development of a Dynamic Model and Thermal Management Strategies for High-Temperature Sodium Sulfur Batteries

The sodium sulfur battery is an advanced secondary battery, which can be used for grid-level storage applications. At the grid level, sodium-sulfur batteries have high potential for electrical storage due to their high energy density, low cost of the reactants, and high open-circuit voltage. In a grid-connected system, sodium-sulfur batteries need to operate under high current density that can cause cell deterioration, lower sulfur utilization and lower energy efficiency. Furthermore, in the absence of an efficient thermal management strategy, unsafe temperature excursion may occur. To study the transient response of sodium-sulfur batteries under high current density operation and to develop efficient thermal management strategies, a thermo-electrochemical dynamic model of a sodium-sulfur battery has been developed.

First a high-fidelity model of the cell is developed. The thermal model of the cell considers heat generation due to Ohmic loss, Peltier heat, and heat due to the entropy change. Species conservation equations are written in the sulfur electrode for the chemical and ionic species by considering the phase transition and change in the composition depending on the state of discharge (SOD). The electrochemical reactions are modeled by using Arrhenius-type rate equations with temperature-dependent terms and varying species concentration depending on the SOD. Species conservation equations are written in the beta”-alumina electrolyte for the ionic species by considering the effect of diffusion and migration. In addition, the potential distribution, cell resistance, and energy conservation have been modeled. In addition, a thermo-electrochemical model is also developed for the sodium electrode. The physicochemical properties are considered to be temperature-dependent.

However, the cell model is computationally intractable for modeling the battery. A number of strategies are implemented similar to the work of Northrop et al. (2011). These strategies include coordinate transformation, orthogonal collocation, and model reformulation. The reduced order model solves significantly faster than the full, high-dimensional model but provides an accurate estimate of the key variables. It is observed that significant excursion in the battery temperature can occur under aggressive charging/discharging scenarios especially if the current density is high. A novel thermal management strategy is developed to maintain the battery temperature within acceptable limits.

Reference

(1)               Northrop PWC, Ramadesigan V, De S, and Subramanian VR, “Coordinate Transformation, Orthogonal Collocation, Model Reformulation and Simulation of Electrochemical-Thermal Behavior of Lithium-Ion Battery Stacks”, 158, A1461-A1477, Journal of the Electrochemical Society, 2011