Analysis of elastic, plastic, and creep properties of sodium metal and implications for solid-state batteries

Abstract

Na metal has garnered attention as an anode because of its high specific capacity, low potential and abundance compared to Li metal. With continued development of fast Na-ion conductors, solid-state Na metal batteries present a solution for low-cost batteries with high energy densities. However, many of the rate-limitations in solid-state batteries are hypothesized to relate to the physical properties of the metal anode, necessitating a better understanding of the mechanical behavior of alkali metals. In this study, various analyses were performed to gain insight into the mechanical properties of Na metal at room temperature. Tensile/compressive tests were performed on Na metal using a load-frame in an inert environment, demonstrating a yield strength between 0.19 and 0.28 MPa at a strain-rate of ~10−3 s−1. An elastic modulus of 4.6 GPa was measured using acoustic techniques. Because of its low melting temperature, deformation of Na is highly influenced by creep. A stress exponent was measured to be 5.0, suggesting dislocation climb as the rate-controlling mechanism. Lastly, to better understand how the mechanical behavior will affect performance, compression tests were performed on substrates germane to solid-state cells. The mechanical properties presented in this work may provide new insights in the design, modeling, and understanding of solid-state batteries utilizing alkali metal anodes.