科研之友
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摘要
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)64?‐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.(#br)The proposed bidirectional tandem electrocatalysis facilitates successive reversible conversion of both long‐ and short‐chain polysulfides, whereas porous Fe2O3 core serves as the main reactor and accelerates long‐chain Na2S8/Na2S6 to Na2S4 conversion and the redox‐active Fe CN)64?‐doped polypyrrole shell functions as physical barrier and catalyzes confined short‐chain Na2S4 reduction to final Na2S inside the nanopores.
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