Hengyue Xu
Understanding how curved molecular carbon interfaces regulate sulfur redox remains a central challenge for the rational design of advanced Li–S and Na–S batteries. Here, we present a systematic theoretical study of sulfur species adsorbed on C 60 and establish a mechanistic framework for curvature-gated sulfur redox. The calculated adsorption energies reveal pronounced chain-length-dependent stabilization on C 60, with terminal short-chain sulfides being most strongly bound, including C 60 -Li 2 S and C 60 -Na 2 S. Gibbs free-energy analysis further shows that both Li–S and Na–S pathways share a common thermodynamic bottleneck at the M 2 S 4 → M 2 S 2 conversion step, with uphill free-energy changes of +0.76 eV and +0.83 eV, respectively. Electronic-structure analyses demonstrate that this selective stabilization is governed by interfacial polarization rather than geometric confinement alone and evolves from weak contact for neutral sulfur to predominantly electrostatic interaction for intermediate-chain sulfides and a hybrid covalent-electrostatic mode for terminal sulfides. At the orbital level, both C 60 -Li 2 S and C 60 -Na 2 S exhibit a common motif consisting of a fullerene-centered low-lying acceptor manifold and mixed occupied interfacial frontier states. Most importantly, although Na 2 S binds more strongly to C 60 than Li 2 S, its final Na–S bond-cleavage barrier (1.05 eV) is markedly lower than the corresponding Li–S bond-cleavage barrier (1.48 eV), showing that Na 2 S is kinetically more labile than Li 2 S on the same curved carbon interface. These results identify C 60 as a curvature-gated reaction interface that reshapes sulfur redox through stage-selective thermodynamic bias, polarization-governed stabilization, and metal-dependent terminal conversion kinetics.