(49e) Optimal Thermal Management of a High-Temperature Sodium Sulphur Battery

Sai Pushpitha Vudata, Debangsu Bhattacharyya, Richard Turton

Department of Chemical and Biomedical Engineering, West Virginia University, Morgantown, WV 26506, USA

The sodium sulfur battery is an advanced secondary battery with high potential for grid-level storage due to their high energy density, low cost of the reactants, and high open-circuit voltage. However, as the current density is high and the normal operating temperature of the battery is high (about 300^oC), effective thermal management is required to prevent thermal runaway. This work proposes a hybrid cooling strategy– a combination of active and passive methods- that not only results in effective thermal management but also utilization of the heat for better energy efficiency. The cooling strategies will be implemented by an optimal method based on a control variable.

To study the transient response of sodium-sulfur batteries under high current density operation and to develop efficient optimal thermal management strategies, a detailed, thermo-electrochemical dynamic model of a sodium-sulfur cell is developed. However, the cell model is computationally intractable for simulating the large number of cells in the battery. Various strategies such as coordinate transformation, orthogonal collocation, and model reformulation (Northrop et al., 2011) are implemented to obtain a reduced order model that solves significantly faster than the full, high-dimensional model but provides an accurate estimate of the key variables.

Under rapid charging/discharging, especially under discharging conditions, it can lead to significant excursion in the battery temperature when the current density is high. Three thermal management strategies are considered in this work: active cooling, passive cooling, and hybrid cooling. The active cooling strategy uses air as the cooling medium whereas, the passive cooling strategy uses a phase change material (PCM) to serve as the thermal storage offsetting the transients. The passive cooling strategy provides faster heat dissipation than the active cooling strategy especially during high pulse power discharges while maintaining sufficiently uniform cell temperature. However, it was observed that the passive cooling strategy can lead to high heat accumulation in the PCM especially under very high current density and discharging conditions. This can eventually lead to thermal runaway. A hybrid cooling strategy is developed that can not only maintain the cell temperature near the optimum under rapid cycling operation at high current density, but can effectively utilize the heat improving the overall efficiency of the battery system.

Reference

• 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