(Invited) Intermetallics Based on Sodium Chalcogenides Promote Stable Electrodeposition – Electrodissolution of Sodium Metal Anodes

Sodiophilic micro-composite films of sodium-chalcogenide intermetallics (Na2Te and Na2S) and Cu particles are fabricated onto commercial copper foam current collectors (Na2Te@CF and Na2S@CF). For the first time a controllable capacity thermal infusion process is demonstrated. Enhanced wetting by the metal electrodeposition leads to state-of-the-art electrochemical performance. For example, Na2Te@CF-based half-cells demonstrate stable cycling at 6 mA cm-2 and 6 mAh cm-2, corresponding to 54 μm of Na electrodeposited/electrodissolved by geometric area. Sodium metal battery (SMB, NMB) cells with Na3V2(PO4)3 (NVP) cathodes are stable at 30C (7 mA cm-2) and for 10,000 cycles at 5C and 10C. Cross-sectional cryogenic focused ion beam (cryo-FIB) microscopy details deposited and remnant dissolved microstructures. Sodium metal deposited onto Na2Te@CF is dense, smooth, and free of dendrites or pores. On unmodified copper foam, sodium grows in a filament-like manner, not requiring cycling to achieve this geometry. Substrate-metal interaction critically affects the metal-electrolyte interface, namely the thickness and morphology of the solid electrolyte interphase (SEI). Density functional theory (DFT) and mesoscale simulations provide insight into support-adatom energetics, nucleation response, and early-stage morphological evolution. On Na2Te sodium atomic dispersion is thermodynamically more stable than isolated clusters, leading to conformal adatom coverage of the surface.