Date of Award

December 2015

Degree Type

Thesis

Degree Name

Master of Science

Department

Engineering

First Advisor

Chang Soo Kim

Committee Members

Benjamin C. Church, Junhong Chen

Keywords

FEA, Finite Element Analysis, NaS, Sodium, Sulfur, Thermomechnical Stress

Abstract

The importance of a reliable and safe way to store energy, and allow for on-demand usage, has led to much research in the field of secondary battery development. The thesis herein explores a technology that has shown promising results when implemented in large-scale energy grid applications. Though the technology has proven viable in both load-leveling on existing grids as well as serving to legitimize renewable energy sources, the development of such advanced battery systems is not without challenge. Sodium-sulfur (NaS) secondary cells have shown promising results when implemented in the aforementioned energy storage applications. One of the main drawbacks to this technology however, is that the cells must operate at elevated temperatures (~350°C) for facile transport of active materials. The high operating temperatures keep the highly reactive molten electrodes in the liquid phase, which can lead to catastrophic failure if not properly contained. This has led much research in the direction of safety advancements while maintaining the overall desired cell output efficiency. The complexity of the thermal loading conditions induced during the production sequence and subsequent operation has made successful development both difficult and expense. In particular, the stress accumulation in the cell joint areas are of high concern. Through the incorporation of finite element analysis (FEA), the complexities of the intricate cell design, and influences from thermomechanical stresses can be studied more easily. In this work, several computational models of the cell have been developed to predict the thermally induced stress concentrations on the various components within the planar-type NaS cell. The ABAQUS commercial software package (Hibbit Karlson & Sorences Inc. Pawtucket, RI, USA) was implemented to perform the computational analyzes. Throughout the current work, the impacts of geometrical and material specific properties were modified to quantify the impacts of those variables on the resultant stress accumulations. The development of the current models can be used to accurately predict the relative induced motions of the dissimilar materials within the cell. From the results, the highest thermal stress concentration areas, with corresponding stress values in the cell, were predicted. Additionally, by modifying the coefficients of thermal expansion (CTE) values of the various materials; the resultant normal and shear stress concentrations during temperature cycling were investigated. It is anticipated that the developed computational model can be readily applied to select the constituent materials and to optimize the cell design toward enhanced stability and safety.

Download

Share

COinS