Tuning dual-atom mediator toward high-rate bidirectional polysulfide conversion in Li-S batteries

Abstract

An emerging practice in the realm of Li-S batteries lies in the employment of single-atom catalysts (SACs) as effective mediators to promote polysulfide conversion, but monometallic SACs affording isolated geometric dispersion and sole electronic configuration limit the catalytic benefits and curtail the cell performance. Here, we propose a class of dual-atom catalytic moieties comprising hetero- or homo-atomic pairs anchored on N-doped graphene (NG) to unlock the liquid–solid redox puzzle of sulfur, readily realizing Li-S full cell under high-rate-charging conditions. As for Fe-Ni-NG, in-depth experimental and theoretical analysis reveal that the hetero-atomic orbital coupling leads to altered energy levels, unique electronic structures, and varied Fe oxidation states in comparison with homo-atomic structures (Fe-Fe-NG or Ni-Ni-NG). This would weaken the bonding energy of polysulfide intermediates and thus enable facile electrochemical kinetics to gain rapid liquid-solid Li2S4 ↔ Li2S conversion. Encouragingly, a Li-S battery based on the S@Fe-Ni-NG cathode demonstrates unprecedented fast-charging capability, documenting impressive rate performance (542.7 mA h g−1 at 10.0 C) and favorable cyclic stability (a capacity decay of 0.016% per cycle over 3000 cycles at 10.0 C). This finding offers insights to the rational design and application of dual-atom mediators for Li-S batteries.