1. Selection of Container Materials for NaS Batteries towards Higher Thermo-mechanical Stability
Yihan Xu and Chang-Soo Kim
Materials Science and Engineering Department
University of Wisconsin-Milwaukee
April 2018

2. Introduction to Sodium Sulfur (NaS) Batteries
Advantages: high energy density, long discharge time, long lifetime, no self-discharge, and low manufacturing costs.
Applications: grid scale energy storage systems.

3. fracture from the outer surface of IH
Objectives
The thermo-mechanical stress concentrates in the sealing areas during the cell assembly and/or operation processes, especially for planar cells with increasing cell sizes.
fracture from the outer surface of IH
We introduce the FEA approach to address the quantitative assessment of such thermo-mechanical stress concentrations.
Modeling Procedure:
Design cell structure  Construct 3D structure using hyperMesh  Apply BCs, impose static thermal load  ABAQUS solver
Planar NaS cells
K. Jung et al. Journal of Power Sources 324 (2016)
The impacts of the cell container material types on the thermo-mechanical behavior of the cell will be explored.

4. Deformations and von-Mises Stress Distributions
Y. Xu et al. Journal of Energy Storage 12 (2017) 215–225.
Whole cells
Cell joint areas

5. Thermo-mechanical Stress Distribution/Accumulation
The normal bonding strength of IH/IM is measured as 40~80 Mpa

6. Summary
It is suggested to use KOVAR or other alloys to have CTE values smaller than those of STS430 when the planar NaS cell size is large (i.e., greater than 90 mm of BASE disk diameter).
It is expected that the current computational model could be readily applied to guide the material selections and to test the thermo-mechanical stability (predict the most likely regions and conditions of potential thermo-mechanical fracture) of contemporary planar NaS cells towards advanced large scale energy storage systems.

7. Acknowledgements
This work was supported by POSCO, Korea Institute of Energy Technology Evaluation and Planning (KETEP) under the authority of the Ministry of Trade, Industry, and Energy of the Republic of Korea, and US Department of Energy (US DoE) (No ).