Mechanistic Analysis of Solid Electrolyte Interphase Interactions in Sodium Metal Electrodes

Sodium (Na) metal batteries have emerged as promising candidates for next-generation low-cost energy storage systems. However, the formation of a heterogeneous solid electrolyte interphase (SEI) at the anode results in high interfacial resistances and morphological instabilities, posing a major challenge for the practical implementation of Na metal batteries. Heterogeneities in the SEI can lead to ionic transport limitations and influence the reaction distribution at the Na/SEI interface. The resulting current heterogeneity induces non-uniform morphological growth and stress hotspots in the SEI. In this work, we develop a spatiotemporal mesoscale model to study the mechanics-coupled electrochemical interactions governing the electrodeposition stability of Na metal electrodes. We reveal that the evolution of mechanical stresses in the SEI and Na metal strongly influences the reaction kinetics by altering the mechanical overpotential. We analyze the effect of electrochemical and mechanical properties of the SEI on interface growth and onset of cell failure. Three distinct SEI failure modes primarily driven by the mechanical, transport, and reaction kinetic interactions at the Na/SEI interface have been delineated.