Self-supported hierarchically porous 3D carbon nanofiber network comprising Ni/Co/NiCo2O4 nanocrystals and hollow N-doped C nanocages as sulfur host for highly reversible Li–S batteries

Abstract

Hierarchically porous nitrogen-doped carbon nanofibers (P-N-CNF) comprise well-embedded metallic-Ni/Co and spinel-type NiCo2O4 nanocrystals (Ni-Co/NiCo2O4) along with metal-organic framework-derived hollow nitrogen-doped carbon nanocages (HNC), denoted as P-N-CNF@NCO/HNC, are rationally designed as cathode substrates for advanced lithium-sulfur batteries with feasible parameters. The highly conductive and porous N-CNF matrix provides numerous conductive channels for rapid ionic and electronic transfer. HNC guarantees efficient impregnation of a large volume of active material along with high loading, channelizing the volume variation stress, and ensuring efficient electrolyte percolation, which is crucial for uniform dispersion and high active sulfur utilization, especially at low electrolyte/sulfur (E/S) ratios. The metallic-Ni/Co and polar spinel-type NiCo2O4 nanoparticles offer sufficient chemisorption sites to prevent polysulfide migration towards the anode. Li-S cells assembled using P-N-CNF@NCO/HNC as an advanced host and lithium polysulfide catholyte as the starting material displayed stable electrochemical performance even with strident battery parameters, including high sulfur content (79.8 wt%), high sulfur loading (7.7 mg cm−2), and low E/S ratio (8.0 µL mg−1). The cell displays a maximum areal capacity of 5.4 mA h cm−2 that stabilizes to 2.8 mA h cm−2 after 160 cycles at 0.1 C and is comparable to the theoretical threshold of presently available commercial systems.