Hierarchically porous carbon derived from delignified biomass for high sulfur-loading room-temperature sodium-sulfur batteries

The commercial applications of room-temperature sodium-sulfur battery still suffers from low sulfur utilization and poor reaction kinetics. Here, we develop a novel carbon material with hierarchical pores from camellia oleifera seed cake as the host of sulfur by introducing a delignification process followed by KOH activation. The large specific surface area (1362 m2 g−1) and well-developed porosity produced by the two-step method make it possible to realize high sulfur content (61.9 wt%). By the physical confinement of micropores, the formation of Na2Sx (4 ≤ x ≤ 8) is effectively suppressed to avoid the side reactions. The mesopores and macropores optimize the electrolyte accessibility. The sulfur-loaded carbon cathode delivers a reversible capacity of 702 mAh g−1 after 100 cycles at 0.1 C (1 C = 1675 mAh g−1). Even at 1 C, a reversible capacity of 404 mAh g−1 has been achieved after 300 cycles. This work demonstrates a sustainable cathode with a high sulfur content for the practical application of room-temperature Na–S batteries.