Fundamental Investigation of Lithium–Sulfur Battery Cathodes with Controlled Sulfur Content in Activated Carbon by Electrochemical Techniques

Lithium–sulfur (Li–S) batteries are considered promising energy storage systems due to their high theoretical energy density and the abundance of sulfur. However, their performance strongly depends on the cathode architecture and sulfur distribution within the carbon host. In this work, we present a fundamental investigation of sulfur cathodes supported on graphene, graphite, and activated carbon (AC) under identical synthesis and testing conditions. AC proved to be the most effective host owing to its high surface area, large pore volume, and oxygen-containing functional groups, which promote strong chemical interactions with sulfur and mitigate the shuttle effect. Among the tested AC/S mass ratios (10:6 to 10:30, w/w), the 10:10 composition provided the best balance between conductivity, electrochemical accessibility, and mechanical stability, delivering an initial capacity of 2.3 mA h at 0.1 C and retaining ∼64% after 600 cycles at 1 C, with a low decay rate (0.076% per cycle) and stable cycling up to 1000 cycles. These results highlight how systematic control of sulfur content and carbon host structure provides a valuable understanding of sulfur utilization and cycling stability in Li–S batteries, offering a mechanistic basis for the rational design of future high-loading electrodes.