Polysulfide regulation by defect-modulated Ta₃N_5-x electrocatalyst toward superior room-temperature sodium-sulfur batteries

Resolving low sulfur reaction activity and severe polysulfide dissolution remains challenging in metalsulfur batteries. Motivated by a theoretical prediction, herein, we strategically propose nitrogenvacancy tantalum nitride (Ta3N5-x) impregnated inside the interconnected nanopores of nitrogendecorated carbon matrix as a new electrocatalyst for regulating sulfur redox reactions in roomtemperature sodium-sulfur batteries. Through a pore-constriction mechanism, the nitrogen vacancies are controllably constructed during the nucleation of Ta3N5-x. The defect manipulation on the local environment enables well-regulated Ta 5d-orbital energy level, not only modulating band structure toward enhanced intrinsic conductivity of Ta-based materials, but also promoting polysulfide stabilization and achieving bifunctional catalytic capability toward completely reversible polysulfide conversion. Moreover, the interconnected continuous Ta3N5-x-in-pore structure facilitates electron and sodium-ion transport and accommodates volume expansion of sulfur species while suppressing their shuttle behavior. Due to these attributes, the as-developed Ta3N5-x-based electrode achieves superior rate capability of 730 mAh g(-1) at 3.35 A g(-1), long-term cycling stability over 2000 cycles, and high areal capacity over 6 mAh cm(-2) under high sulfur loading of 6.2 mg cm(-2). This work not only presents a new sulfur electrocatalyst candidate for metal-sulfur batteries, but also sheds light on the controllable material design of defect structure in hopes of inspiring new ideas and directions for future research. (c) 2023 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.