A stable anode-free Na-S full cell at room temperature

Abstract

The extended cycling life of room-temperature Na-S batteries depends predominantly on the excessive Na metal. Inhibiting Na corrosion by soluble Na polysulfides (NaPS) and reducing the usage of Na metal are key challenges to achieve practical Na-S batteries. Herein, an anode-free Na-S full cell is assembled with Na2S@carbon paper cathode prepared by in situ carbon-thermal reduction of Na2SO4, and 3D current collector (3DCC) of carbon nanofibers at the anode side, extraordinarily using Fluoroethylene carbonate (FEC) as electrolyte additive. This Na2S-based 3DCC||Na2S full cell not only provides stoichiometric Na source but also permits FEC to participate in formation of SEI on 3DCC ahead of the production of soluble NaPS during the initial charging, overcoming the incompatibility of FEC in Na-S battery. The polysulfide-resistant SEI guarantees the stable plating/stripping of volume-expansion alleviated Na metal on 3DCC. The as-developed anode-free 3DCC||Na2S full cell demonstrates 500-cycle life at 0.5 C, delivering much higher overall energy density than those using excessive Na metal. This is the first report of rechargeable anode-free Na-S battery with satisfactory cycling durability, representing a significant step toward achieving practical Na-S batteries.