Room-temperature metal–sulfur batteries have attracted extensive interest because of their advantages of high theoretical capacity, high elemental abundance, and low cost. Towards improving the electrochemical performances of the sulfurized polyacrylonitrile (SPAN) composite cathode in potassium–sulfur batteries (KSBs), an advanced electrode design has been developed by applying a polyacrylic acid (PAA) binder to the SPAN electrode. By integrating the merit of the SPAN composite cathode and PAA binder, the proposed SPAN cell generates a high reversible capacity of 1,050 mA h g^-1 and has excellent cycling stability after 100 cycles (95% retention of the initial cycle) at a high current density of 837.5 mA g^-1 . Ex situ Raman spectra show that the PAA binder is evidently more effective at improving the structural stability of the SPAN electrode than the PVdF binder during cycling. Despite the large volume changes during reduction/oxidation steps in the wide voltage window of 0.1–3.0 V, the SPAN electrode with the PAA binder gave an excellent electrochemical performance in KSBs. To better understand the electrochemical reaction mechanism of SPAN in KSBs, XPS analysis was further performed in a wide discharge cut-off voltage range.