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The practical application of lithium-sulfur batteries is usually hindered by the unstable discharge intermediates and the low conductivity of the sulfur cathode. Herein, we propose to improve the performance of the sulfur cathode by introducing a built-in carbon nanotube network inside a biomass-derived hierarchically porous carbon for the subsequent sulfur loading. This balanced structural design of the carbon substrate enables effective trapping of active sulfur within the cathode and provides a highly efficient pathway for electron transmission, contributing to an increased conductivity and structural integrity of the cathode. By using a potentiostatic process at the end of charge, the reversibility of the electrode reaction of sulfur is improved. The sulfur cathode delivers an initial discharge capacity of 1739 mA h g−1 and reaches a high initial Columbic efficiency of 87.6 %, and maintains its efficiency to >97.5 % from the 2nd cycle. It also shows admirable cycling and rate performance.

Inspired by the egg-like yolk–shell structure, a novel kind of graphene-wrapped graphitic hollow carbon spheres (G-graphitic HCS) was designed and fabricated by iron-catalyzed carbonization of double-coated polystyrene (PS) spheres. Herein, a thin carbon shell and hollow, hierarchically porous G-graphitic HCS facilitate ionic transport, while also providing more active sites for the storage of ions. Both graphitic components result in a seamless and highly efficient transmission pathway for electrons. Thus, G-graphitic HCS demonstrate admirable multifunctions in energy-storage devices, including lithium batteries, sodium batteries, and supercapacitors. It delivers an unprecedentedly high initial discharge capacity of 2007 mA h g−1 at 0.1 A g−1, and preserves 92.4 % of the initial charge capacity after 100 cycles in a prototype lithium half-cell. The present concept may shed light on designing the key materials for next-generation energy-storage devices.