Orthorhombic Nb2O5 Decorated Carbon Nanoreactors Enable Bidirectionally Regulated Redox Behaviors in Room-Temperature Na–S Batteries

Regulating redox kinetics is able to spur the great-leap-forward development of room-temperature sodium–sulfur (RT Na–S) batteries, especially on propelling their Na-ion storage capability. Here, an innovative metal oxide kinetics accelerator, orthorhombic Nb2O5 Na-ion conductor, is proposed to functionalize porous carbon nanoreactors (CNR) for S cathodes. The Nb2O5 is shown to chemically immobilize sodium polysulfides via strong affinity. Theoretical and experimental evidence reveals that the Nb2O5 can bidirectionally regulate redox behaviors of S cathodes, which accelerates reduction conversions from polysulfides to sulfides as well as promotes oxidation reactions from sulfides to S. In situ and ex situ characterization techniques further verify its electrochemical lasting endurance in catalyzing S conversions. The well-designed S cathode demonstrates a high specific capacity of 1377 mA h g−1 at 0.1 A g−1, outstanding rate capability of 405 mA h g−1 at 2 A g−1, and stable cyclability with a capacity retention of 617 mA h g−1 over 600 cycles at 0.5 A g−1. An ultralow capacity decay rate of 0.0193% per cycle is successfully realized, superior to those of current state-of-the-art RT Na–S batteries. This design also suits emerging Na–Se batteries, which contribute to outstanding electrochemical performance as well.