Elucidating solid electrolyte interphase formation in sodium-based batteries: key reductive reactions and inorganic composition

Abstract

Sodium-based batteries, due to their abundant and inexpensive resources, have emerged as promising candidates for next-generation high-energy battery systems. Nonetheless, the large-scale commercial application of these batteries remains hindered by the formation of dendritic and mossy-like microstructures on the sodium metal anode, accompanied by an unstable solid electrolyte interphase (SEI), which results in reduced coulombic efficiency (CE) and increased safety risks. Despite significant progress in developing Na-metal anodes, the fundamental understanding of the SEI remains unclear. In this study, a hybrid ab initio and reactive molecular dynamics (HAIR) approach is employed to elucidate the initial reductive reactions towards SEI formation by analysing detailed molecular dynamics simulation trajectories. The formation processes of OH⁻ and CO₃²⁻, crucial components of the SEI layer, are identified, consistent with experimental observations. To further validate the simulation results, radial distribution function (RDF), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) patterns are simulated following long-duration (2.8 ns) HAIR simulations. NaOH, NaF, and Na₂CO₃ are identified as the inorganic components of the SEI, aligning with experimental findings.