Optimizing Mid-Temperature Sodium Iodine Batteries for Sustainable Large-Scale Energy Storage: A Comprehensive Modeling Approach and Experimental Validation
Authors: Gerbig Felix , Schäfer Frank , Holzapfel Michael , Nirschl Hermann 
Published: August 2024

The need for safe, eco-friendly, low-cost batteries for large scale implementation rises in the presence of the expansions of renewable energy sources. High-temperature liquid sodium batteries (e.g. sodium-sulfur) are a well-established technology for large-scale grid storage. Combining the molten sodium anode with an aqueous iodine cathode overcomes the problems of thermal loses and sealing by reducing the operating temperature to about 100°C. This leads to higher cost efficiency, energy density and a simplified cell design.
Here we present a novel modelling approach for complex carbon-based cathode structures and its limits and abilities on enhancing the utilizable capacity. Due to their sustainability and high efficiency, which is comparable to Li-Ion –batteries, mid-temperature sodium-iodine batteries are a promising candidate for stationary energy storage applications. With a high specific energy of around 200 Wh kg-1, sodium-iodine batteries have the ability to meet the growing demand of short-term energy storage caused by the integration of renewable energy sources into the power grid. Up to this day, the detailed processes inside the battery are not well-understood. Quantities like initial species concentrations, C-rate, cell design and cathode geometry have large impacts on the overall battery performance. A deeper understanding of these processes is inevitable for enhancing the battery performance by choosing the optimal abovementioned quantities. We set up a fully resolved 3D Simulation model to gain insight into microstructural processes inside the battery, as experimental studies are limited to macroscopic quantities like electronic current and potential. The methodology is based on continuum hypothesis by using an open-source CFD software, which is rewritten accordingly. The proposed spatially resolved three-dimensional simulation model takes charge and mass transport, heterogeneous and homogeneous reactions as well as the electrochemical processes into account. Results show that transport limitations confine the utilizable capacity of the battery [1].
This contribution focuses on enhancing the battery energy density and efficiency by including open-pored glassy carbon foam structures in the cathode half-cell [2, 3]. We state simulation predicted, optimal morphology properties of such a structure. Furthermore, we describe the evaluation of improved thermodynamic data of the aqueous iodine solution by refitting simulation results to polarization curves. We utilize a novel impedance spectroscopy simulation method for sodium iodine batteries to improve parameterization of the underlying electrochemical model by comparing the results with experimental data.

References

Gerbig, F., Cernak, S., Nirschl, H. (2021). 3D Simulation of Cell Design Influences on Sodium–Iodine Battery Performance. Energy Technology, vol. 9, no. 6, p. 2000857

Gerbig, F., Cernak, S. and Nirschl H. (2021), Towards a Novel Sodium-Iodine Battery with an Aqueous Catholyte: Numerical Investigations of Complex Cathode Structures, ECS Trans., vol. 104, no. 1, pp. 123–130

Gerbig, M. Holzapfel, and H. Nirschl, Simulating the Impact of Glassy Carbon Foam Electrodes on the Performance of Sodium Iodine Batteries, J. Electrochem. Soc., vol. 170, no. 4, p. 40517, 2023, doi: 10.1149/1945-7111/accab7.

Figure 1