(40i) 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