Role of thermal gradient in interface stability of sodium metal electrodes

Abstract

The practical implementation of sodium (Na) metal electrodes is hindered by challenges such as dendrite growth and low coulombic efficiency. The morphological stability of the metal-electrolyte interface is strongly governed by coupled thermal phenomena that alter the underlying chemo-mechanical interactions. In this study, we investigate the role of operating temperature and thermal gradients in influencing ion transport, reaction kinetics, and interface stability during plating and stripping. While an increase in temperature improves ionic mobility and promotes creep-driven stabilization, it is demonstrated that higher temperatures also exacerbate reaction nonuniformity arising from heterogeneity in the solid electrolyte interphase (SEI). A comparative analysis between Na and lithium (Li) reveals that although Na exhibits higher creep rates, its larger molar volume leads to faster filament growth during deposition. Moreover, we show that localized heating within the SEI gives rise to thermal gradients near the metal-electrolyte interface, which in turn drive ionic flux via thermo-diffusion (Soret effect). It is found that thermo-diffusion can either suppress or amplify reaction heterogeneity depending on the direction and magnitude of thermal gradients. This work highlights the critical role of thermal design in enabling safe and stable operation of Na metal anodes across a wide range of operating conditions.