Confinement of sulfur in the micropores of honeycomb-like carbon derived from lignin for lithium-sulfur battery cathode

Abstract

Nitrogen-incorporated honeycomb-like nanoporous carbons (n-hC) are synthesized through the hydrothermal carbonization of a lignin precursor, subsequent KOH activation, and a post-doping process. The as-obtained n-hC exhibits a large surface area (2071 m2 g−1) and pore volume (1.11 cm3 g−1) and a high N content (3.47%). The n-hC is used as an S-hosting material with a mass loading of 64.1 wt% (S@n-hC) through the in situ redox reaction of Na2S2O3. The S@n-hC achieves a high initial discharge capacity of 1295.5 mAh g−1 at 0.1C and retains 647.2 mAh g−1 after 600 cycles, and shows excellent cycling stability (with the capacity fading of 0.05% per cycle over 900 cycles at 1C). The strong confinement of S in the N-incorporated micropores leads to the electrochemical and thermal stabilization of S, providing different redox environments. The facile and reversible redox kinetics of the S@n-hC are confirmed by deriving the lowest exchange current density and redox charge-transfer resistance from Tafel and Nyquist plots and through the prominent redox and charge/discharge profiles. The improved performance of the S@n-hC is attributed to the S confinement in the micropores, the honeycomb-like hierarchical structure, and the N incorporation for the inhibition of polysulfide dissolution and the efficient utilization of S.