Microporous carbon enhanced by structural modifications to suppress polysulfide shuttling and reducing capacity fading in lithium-sulfur batteries

Abstract

Lithium-sulfur batteries (Li-S) commercialization remains complex due to limited cycling stability related to the solubility of polysulfide intermediates, specifically higher-order polysulfides (Li2S4 to Li2S8). Some studies have utilized microporous carbons with pores ≤0.7 nm, which can accommodate only short-chain polysulfides (Li2S2-4) to resolve the challenge of polysulfide shuttling. Yet, the discharge products of long-chained polysulfides, Li2S8 and Li2S6 molecules with diameters of 0.84 nm and 0.76 nm, are not entirely confined in the micropores due to the poor affinity of the carbon host and polysulfides. In this study, we have created a micropore carbon (AC900) with a pore size (1.2 nm) that can accommodate both long and short-chain polysulfides and infiltrated it with sulfur (AC900S). To mitigate capacity fading, we further modified the carbon using urea (AC900NS) and nickel sulfate (AC900S-Ni) treatments. The latter did not result in detectable Ni incorporation but induced partial changes in carbon hybridization and surface structure. The synthesis-driven structural adjustment in AC900S-Ni influenced polysulfide confinement and improved electrochemical stability compared to AC900S and AC900NS. The AC900S-Ni cathode demonstrated a capacity retention of 72% with a capacity of 773 mAh/gS after 100 cycles and 1000 mAh/gS in the first cycle at C/20, higher compared to AC900S and AC900NS. An improvement in capacity retention of 96% was noted at C/10, with a discharge capacity of 722 mAh/gS after 100 cycles, compared to 805 mAh/gS in the first cycle. The results isolate the factor contributing to capacity fading in unmodified AC900S and demonstrate that chemical/structural modification of microporous carbon combined with a carbonate electrolyte provides a promising pathway for Li-S systems. This study offers a facile approach to tune carbon hosts and expand their applicability in Li-S batteries.