Capacity Enhancement and Discharge Mechanisms of Room-Temperature Sodium-Sulfur Batteries

A strategy for capacity and cyclability enhancement of room-temperature sodium-sulfur (Na-S) batteries is reported by inserting a nanostructured, carbon-based interlayer between the sulfur cathode and the separator. The interlayer localizes the soluble polysulfide species and prevents its migration to the sodium anode. Electrochemical and spectroscopic characterizations along with thermodynamic analyses indicate that the charge/discharge of the Na-S cell involves complicated transition processes through a series of long-chain (Na2Sn, 4 <= n <= 8) and short-chain (Na2Sn, 1 <= n <= 4) sodium-polysulfide intermediates. The results obtained in this work show that the cell can provide a remarkable capacity of 400 Ah kg(-1) and an energy density of 720 Wh kg(-1) (based on the sulfur cathode) after 20 cycles.