Bidirectional Tandem Electrocatalysis Manipulated Sulfur Speciation Pathway for High-Capacity and Stable Na-S Battery

The sluggish polysulfide redox kinetics and the uncontrollable sulfur speciation pathway, leading to serious shuttling effect and high activation barrier associated with sulfur cathode. We describe here the use of core-shell structured composite matrixes containing abundant catalytic sites for nearly fully reversible cycling of sulfur cathodes for Na-S batteries. The bidirectional tandem electrocatalysis provide successive reversible conversion of both long- and short-chain polysulfides, whereas Fe2O3 accelerates Na2S8/Na2S6 to Na2S4 conversion and the redox-active Fe(CN)(6)(4-)-doped polypyrrole shell catalyzes Na2S4 reduction to Na2S. The electrochemically reactive Na2S can be readily charged back to sulfur with minimal overpotential. Simultaneously, stable cycling of Na-S pouch cell with a high reversible capacity of 696 mAh g(-1) is also demonstrated. The bidirectional confined tandem catalysis renders the manipulation of sulfur redox electrochemistry for practical Na-S cells.

Automated summary

In this study, core-shell structured composite matrixes were used to achieve nearly fully reversible cycling of sulfur cathodes for Na-S batteries. The bidirectional tandem electrocatalysis enabled successive reversible conversion of both long- and short-chain polysulfides, while Fe2O3 and redox-active Fe(CN)(6)(4-)-doped polypyrrole shell facilitated specific conversions. The electrochemically reactive Na2S could be readily charged back to sulfur, and stable cycling of a Na-S pouch cell with high reversible capacity was demonstrated.