Sodium Intermetallics Enable Stable Sodium Plating and Stripping

Abstract

Sodium-based secondary batteries are emerging as promising complements and potential alternatives to lithium-ion batteries due to their analogous working mechanism but the greater availability of sodium precursors and the other elements making up the cathodes. Sodium metal batteries (SMBs) hold considerable promise due to the high theoretical capacity (1165 mAh g-1) of the metal anode and the associated low plating/stripping potential. Unfortunately, the metal dendrite growth and an associated unstable solid electrolyte interphase (SEI) prevail with SMBs in a wide range of electrolytes. Creating sodiophilic surfaces to promote metal wetting during deposition and simultaneously reduce the nucleation/growth overpotentials has been proven to be highly effective. In this work, a rapid annealing process is employed to fabricate chalcogen (sulfur, tellurium) intermetallic coated commercial copper foam (CF) as stable hosts for Na metal anodes, termed “S@CF” and “Te@CF”. These sodiophilic substrates demonstrate significantly improved sodium wettability, reduced plating/stripping overpotentials, and Coulombic efficiency (CE) in half-cell configurations. Symmetric cells made of Te@CF with thermally infused Na (Te@CF-TNa) showed stable cycling up to 7000 hours and full cells with Te@CF-TNa anodes and Na3V2(PO4)3 (NVP) cathodes give significantly improved rate capability (up to 30C) and cycling (>10000 cycles at 5C and 10C). Moreover, a prototype of a controllable Na thermal infusion process was proposed for the first time. Post-mortem analysis using cryogenic FIB-SEM (Cryo-EM) indicates that the early-stage electrodeposition behavior plays an important role in dictating the later-state electrochemical stability of the metal anodes. Sodium metal electrodeposits uniformly on the surface of Te@CF, resulting in dense and largely pore-free metal. By contrast, electrodeposition on the baseline uncoated CF collector results in filament-like sodium metal dendrites interspersed with pores and a solid electrolyte interphase (SEI). Density functional theory (DFT) and mesoscale calculations provide combined insights into the relationship between the substrate-metal interaction and the nucleation response, describing the underlying mechanisms that tailor an improved Na deposition morphology on the Te@CF substrate.