Investigating the Mechanical Properties of Na Metal for Solid-State Batteries

Abstract

In recent years, increasing power density and reducing cost has fueled interest in developing all solid-state batteries. Na metal anodes have garnered attention because of its abundance and high theoretical capacity (1165 mA h g–1) [1]. However, similar to solid-state Li-ion conductors, it has been reported that dendrite growth through Na-ion conductors also occurs. It has been hypothesized that dendrite propagation through the electrolyte is dependent upon the elastic and plastic properties of the alkali metal anode [2]. Therefore, a better understanding of the mechanical properties of bulk Na can promote the further development of Na-based solid-state batteries.In this study, several analyses were performed to gain insight into the mechanical properties of Na metal. Tensile and compressive tests were performed by using a load frame contained in an inert atmosphere. From the resulting stress-strain graphs, the yield strength was determined to be 0.283 MPa. An acoustic technique was employed to determine that the elastic modulus of Na was 4.6 GPa. Because Na has a relatively low melting point (98°C), the deformation mechanism of Na during battery operation is likely dominated by creep. To investigate the creep behavior of Na, tension creep measurements were performed. The creep exponent of Na was determined to be n = 7.4. Lastly, to better understand the mechanical behavior of Na at the various interfaces in a solid-state battery, compression tests were performed on varying substrates. Three interfaces were examined: Oil/Na (simulating a frictionless interface), current collector/Na, and Na/Na-β’’-alumina.We believe the mechanical measurements in this work will provide new insights into in the design requirements for solid-state batteries utilizing Na metal anodes.REFERENCE 1. Sun, B., Li, P., Zhang, J., Wang, D., Munroe, P., Wang, C., ... & Wang, G. (2018). Dendrite‐Free Sodium‐Metal Anodes for High‐Energy Sodium‐Metal Batteries. Advanced Materials, 30(29), 1801334.2. LePage, W. S., Chen, Y., Kazyak, E., Chen, K. H., Sanchez, A. J., Poli, A., ... & Dasgupta, N. P. (2019). Lithium Mechanics: Roles of Strain Rate and Temperature and Implications for Lithium Metal Batteries. Journal of The Electrochemical Society, 166(2), A89-A97.