High-energy density room temperature sodium-sulfur battery enabled by sodium polysulfide catholyte and carbon cloth current collector decorated with MnO2 nanoarrays

The sodium-sulfur (Na-S) battery is a well-known large-scale electrochemical storage option. The disadvantages of this particular battery technology result from its high operation temperature. Room temperature sodiumsulfur (RT Na-S) batteries would overcome these issues, but have issues of their own, such as rapid capacity decay caused by the polysulfide shuttle and low usage of active material resulting from the insulating nature of sulfur and the final discharge product. Here, we prepare a free-standing cathode using manganese dioxide decorated carbon cloth (CC@ MnO2) as an electronically-conducting substrate and polysulfide reservoir, and sodium polysulfide (Na2S6) catholyte as the active material. Without incorporating any active interlayer, nor an expensive ion-selective membrane (such as Nafion), this free-standing cathode exhibits an initial reversible specific capacity of 938 mA h g(-1) with remarkable capacity retention of 67% after 500 cycles. The as-assembled RT Na-S cell operates at an average potential of 1.82 V and delivered an initial energy density (based on the mass and molecular weight of sulfur and sodium) of 946Wh kg(-1), retained an energy density of 855 Wh kg(-1) after 50 cycles, and attend energy density of 728Wh kg(-1) after 500 cycles. Furthermore, the nature of the interactions between MnO2 and the intermediate polysulfides is investigated by X-ray photoelectron spectroscopy.