▎ 摘　　要

NOVELTY - Cathode active material (I), is new. USE - The material useful for potassium ion battery, preferably potassium ion secondary battery (claimed). ADVANTAGE - The material has high oxidation-reduction potential by using polyanion including sulfur-oxygen bond with high electronegativity in the structure, has rhombohedral crystal structure, contains vacancies through which ions can be inserted/desorbed, has short distance of the ion diffusion path, improves the conductivity, maximizes the conductivity by conductive carbon attached to the surface, suppresses the volume expansion during charging and discharging, has excellent electrochemical performance such as high capacity and operating voltage, and has excellent capacity retention during charging and discharging. DETAILED DESCRIPTION - Cathode active material of formula Fe 2(S aO b) 3 (I), is new. a=1-5; and b=2-9. INDEPENDENT CLAIMS are also included for: manufacturing cathode active material; and potassium ion secondary battery comprising cathode coated with cathode active material, potassium anode facing cathode, and electrolyte disposed between the anode and cathode. DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of the cathode active material.