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

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.