Atomic Manganese Manipulating Polysulfide Speciation Pathway for Room-Temperature Na-S Batteries

Sluggish polysulfide redox kinetics, especially the high energy barrier of rate-determining short-chain polysulfide conversion and the high activation barrier of Na2S decomposition during sulfur recovery, compromise the full potential of rechargeable Na-S electrochemistry. Herein we construct the hierarchical sandwich-structured carbon matrix with atomically dispersed Mn-N4 Lewis acidic sites, taking advantage of their bidirectional electrocatalytic behavior toward interface-mediated reversible sulfur redox. Experimental and theoretical results reveal that the spatial confinement and catalytic effects facilitated via strong Lewis acid-base electron interactions synergistically manipulate the low kinetically direct Na2S4 to Na2S conversion, and the formation of Mn-S bond minimizes the energy barrier of Na2S electrochemical activation during battery recharging, thereby rendering a reversible and tunable polysulfide speciation pathway. Furthermore, the degradation of the Na-S cell is due to the depletion of metal anode rather than the loss of active sulfur species and/or aggregation of inactive dead sulfur. As expected, the S@Mn/NC cathode delivers outstanding rate capability and ultrahigh cycling stability. Simultaneously, a proof-of-concept pouch cell was also demonstrated capable of delivering an energy density up to 840 Wh kgcathode -1. The tunable sulfur redox electrochemistry invoked by the bidirectional monodispersed Mn catalytic hot spots facilitates the efficient polysulfide speciation for practical Na-S cells.