Free-standing 3D network-like cathode based on biomass-derived N-doped carbon/graphene/g-C3N4 hybrid ultrathin sheets as sulfur host for high-rate Li-S battery

Derived from low-cost biomass chitin with hierarchical N-involving molecular structures, a novel renewable N-doping carbonaceous host material (denoted as C-NC) for S cathode in Li-S batteries with 3D network-like structures was fabricated via a facile dissolution and carbonization approach. When incorporated with a small amount of graphene (GN) and g-C3N4, the final products of C-NC/GN/g-C3N4 hybrids maintain the 3D interconnected network-like morphology assembled by 2D ultrathin graphene-like sheets. Meanwhile, the hybrids synergize the advantages of the graphene with high conductivity to facilitate fast electron transfer, the g-C3N4 with efficient chemical absorptivity for intermediate polysulfides to inhibit the unfavorable dissolution, as well as the 3D network frameworks of C-NC with high surface area and macro/mesoporous features to offer rapid ion diffusion channels and adequate electrolyte infiltration and mitigate the structural changes of S cathode during cycling. When loading with elemental S, the fabricated S@C-NC/GN/g-C3N4 cathode shows superior high-rate capability and remarkable cycling performance, which maintains a high reversible capacity of ∼1130 mA h g−1 after 500 consecutive electrochemical cycles. This renewable biomass-based cathode construction strategy offers a low-cost promising approach to design high-rate and ultralong-lifespan Li-S batteries.