Archer group publishes on room-temperature sodium-sulfur batteries in Nature Communications
High-energy rechargeable batteries based on earth-abundant materials are important for mobile and stationary storage technologies. Rechargeable sodium–sulfur batteries able to operate stably at room temperature are among the most sought-after platforms because such cells take advantage of a two-electron-redox process to achieve high storage capacity from inexpensive electrode materials. However, realization of practical room-temperature Na-S batteries has been fraught with multiple stubborn problems ranging from unstable electrodeposition of sodium during battery recharge to rapid loss of the active cathode material by dissolution into the electrolyte. These issues limit the rechargeability, energy density and cycle life of such type of batteries.
Recently Archer group designed a stable room-temperature Na-S battery that uses a sodium metal anode, a microporous carbon-sulfur composite cathode, and a liquid electrolyte containing ionic liquid tethered silica nanoparticles as a deposition stabilizer. The Na-S cells with this configuration can cycle stably for over a hundred cycles with very high reversible capacity at intermediate current density. The high stability and reversibility of the cells stem from at least two sources. First, the tethered silica particles spontaneously form a Na-ion conductive film on the anode, which stabilize deposition of sodium and prevent electrolyte decomposition and depletion. Second, on the cathode side, microporous carbon materials play a key role that can constrain the electrochemical reaction between sodium ion and sulfur to the solid state. This combination of electrolyte and carbon substrate are shown to provide sufficiently strong association of sulfur in the cathode and at the same time stabilize the surface of the highly reactive sodium metal anode.
Reference: Wei, S. et al. A stable room-temperature sodium–sulfur battery. Nat. Commun. 7:11722 doi: 10.1038/ncomms11722 (2016).