Balance of sulfur doping content and conductivity of hard carbon anode for high-performance K-ion storage

•The structural evolution mechanism of S-doped hard carbon is systematically verified through the combination of experimental and theoretical techniques at atomic scale.•SC-700 with a balance of high sulfur doping (7.59 at.%) and excellent sp2 carbon network has been synthesized.•High capacity, excellent rate capability and long-cycle stability are achieved for potassium-ion storage.