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

Abstract

Commercialization of lithium–sulfur batteries (Li–S) 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 pore sizes ≤0.7 nm, which can accommodate only short-chain polysulfides (Li₂S_2–4) to resolve the challenge of polysulfide shuttling. However, the discharge products of long-chain 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 created microporous carbon (AC900) with a pore size of 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 solid-state conversion 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 g_S⁻¹ after 100 cycles and 1000 mAh g_S⁻¹ in the first cycle at C/20, higher than those of AC900S and AC900NS. An improvement in capacity retention to 96% was noted at C/10, with a discharge capacity of 722 mAh g_S⁻¹ after 100 cycles, compared to 805 mAh g_S⁻¹ in the first cycle. The results identify 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.