Abstract <p>Porous carbon from biomass constitutes a cost-effective alternative for producing sustainable cathodes for Li–S cells. The incorporation of iron as heteroatom in a carbon material is suitable to enhance the performance of the cathode in the cell. This study evaluates the optimum percentage of iron incorporated onto porous carbon prepared from Agave bagasse and its effect on the Li–S cell. Low iron percentages were incorporated onto the carbon (0 wt%, 1.5 wt%, 4 wt%, 6 wt%). The SEM images displayed the presence of iron highly dispersed, probably related with the formation of iron carbide. An improvement in stability and discharge capacity of the cell was observed when using carbons with 4% iron (1477 mAhg⁻¹ in cycle 1, and 639 mAhg⁻¹ at cycle 20). Higher iron content did not result in a considerable improvement of the cell, so 4% was considered an optimal value.</p> Graphical abstract <p></p>