Long-life room-temperature sodium-sulfur batteries by virtue of transition metal nanocluster-sulfur interactions.

Room-temperature sodium-sulfur (RT-Na/S) batteries hold significant promise for large-scale application because of low cost of both sodium and sulfur. However, the dissolution of polysulfides into the electrolyte limits practical application. Here, we report the design and testing of a new class of sulfur hosts as transition metal (Fe, Cu, and Ni) nanoclusters (~ 1.2 nm) wreathed on hollow carbon nanospheres (S@M-HC) for RT-Na/S batteries. A chemical couple between the metal nanoclusters and sulfur is hypothesized to assist in immobilization of sulfur and to enhance conductivity and activity. S@Fe-HC exhibited an unprecedented reversible capacity of 394 mAh g-1 despite 1000 cycles at 100 mA g-1, together with the a rate capability of 220 mAh g-1 at a high current density of 5 A g-1. Importantly, density functional theory calculations underscore that these metal nanoclusters serve as electrocatalysts to rapidly reduce Na2S4 into short-chain sulfides and thereby obviate the 'shuttle effect'. We conclude these novel S host cathodes will provide new opportunities to construct electrode materials for various practical battery technologies.