Fast conversion and controlled deposition of lithium (poly)sulfides in lithium-sulfur batteries using high-loading cobalt single atoms

Lithium-sulfur (Li-S) batteries are appealing energy storage technologies owing to their exceptional energy density. Their practical applications, however, are largely compromised by poor cycling stability and rate capability because of detrimental shuffling of polysulfide intermediates, complicated multiphase sulfur redox reactions, and uncontrolled precipitation of the discharge products (lithium sulfide, Li2S). Herein, monodispersed Co single-atom catalyst on conductive nitrogen-doped carbon nanosheet (CoSA-N-C) with high Co content of 15.3 wt% was fabricated through a salt-template method and used as a sulfur host material to simultaneously alleviate the polysulfide shuffling, propel the redox kinetics of dissolved polysulfides, and mediate the deposition of Li2S. The robust two-dimensional architecture of CoSA-N-C with large surface area, high porosity, and dual lithiophilic-sulfiphilic Co-N species enable strong physical and chemical polysulfides confinement and fast electrons/ions transfer process. The densely populated Co-N-4 coordinated moieties function as electrocatalytic sites to accelerate the reversible conversion between lithium polysulfides and Li2S. Importantly, the CoSA-N-C enables spatially controlled deposition of Li2S nanoparticles during the battery discharge process, as opposed to conventional Li2S passivation layers that fully covered the conductive host. Consequently, the as-fabricated cathodes based on the CoSA-N-C deliver high sulfur utilization (1574 mAh-g(-1) at 0.05 C), outstanding rate capability (624 mAh g(-1) at 5 C) and superior long-term stability (capacity fade rate of 0.035% per cycle for 1000 cycles at 1 C). Even under a sulfur loading up to 4.9 mg cm(-2), the reversible areal capacity could reach 4.24 mAh cm(-2) after 120 cycles at 0.2 C, delivering an ultrahigh capacity retention of 91.8%. This work sheds inspiring insights on the important role of single atomic metal with high mass loading in mediating the deposition of lithium sulfides and accelerating the reversible conversion of lithium polysulfides toward decent-performance Li-S batteries.