Fig. 4.

Cycling stability and rate capability of sulfur cathode. a–c Low and high magnification scanning electron microscopy (SEM) images of the NSHG/S₈/Ni cathode (NSHG is nitrogen and sulfur heavily doped graphene). The sulfur cathode was obtained by direct infiltration of NSHG/S₈ hybrid inks into the nickel-deposited carbon fabric (NiCF), followed by drying at 60 °C in a vacuum chamber. Scale bar for a–c is 100 µm, 5 µm, and 500 nm, respectively. d Transmission electron microscopy (TEM) images of NSHG/S₈ cladding layers, extracted from NSHG/S₈/Ni cathode (scale bar = 200 nm). e Specific capacities at various rates for sulfur cathodes, including NSHG/S₈/NiCF, NSHG/S₈/CF (CF is carbon fabric), RGO/S₈/NiCF (RGO is reduced graphene oxide) and Super P/S₈/Al electrodes (Super P is a type of carbon black). f Specific capacities, and corresponding CE values of the optimized NSHG/S₈/NiCF cathode were obtained at 2 mA cm⁻² for 400 cycles. g Cyclic voltammetry curves of NSHG/S₈/NiCF and NSHG/S₈/CF at a scan rate of 0.2 mV s⁻¹ in a potential window from 1.7 to 2.8 V. h Theoretical calculation of the adsorption and decomposition energies of Li₂S on the surface of RGO, nitrogen-doped graphene (NGr), NSHG, and the thin slab of Ni (111). Notably, the thin slab of Ni (111) with a large adsorption energy of −3.51 eV and a tiny decomposition energy barrier of 0.2 eV for Li₂S facilitates the rapid oxidation of Li₂S back to sulfur (carbon is gray, sulfur is yellow, lithium is purple, nitrogen is blue, nickel is light blue)