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

Abstract Sodiophilic micro‐composite films of sodium‐chalcogenide intermetallics (Na 2 Te and Na 2 S) and Cu particles are fabricated onto commercial copper foam current collectors (Na 2 Te@CF and Na 2 S@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, Na 2 Te@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 batteries with Na 3 V 2 (PO 4 ) 3 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 electrodeposition onto Na 2 Te@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. Density functional theory and mesoscale simulations provide insight into support‐adatom energetics, nucleation response, and early‐stage morphological evolution. On Na 2 Te sodium atomic dispersion is thermodynamically more stable than isolated clusters, leading to conformal adatom coverage of the surface.