▎ 摘　　要

NOVELTY - Egg yolk shell structure cathode material i.e. iron-sulfur complex (I), is claimed. the cathode material has egg yolk shell structure, the iron sulfide particles are egg yolk, and the three-dimensional graphene is composed of shell, and the two constitute an egg yolk shell structure; this structure can effectively improve the conductivity of iron sulfide and suppress the volume expansion during the de-doping of potassium ions, so that it can stably and reversibly store potassium ions. USE - The cathode material is useful for potassium ion battery (claimed). ADVANTAGE - The cathode material: has low production cost, strong repeatability, and excellent performance when used as cathode of potassium ion battery. DETAILED DESCRIPTION - Egg yolk shell structure cathode material i.e. iron-sulfur complex of formula (FexS) (I), x = 0.5-1. , is claimed. the cathode material has egg yolk shell structure, the iron sulfide particles are egg yolk, and the three-dimensional graphene is composed of shell, and the two constitute an egg yolk shell structure; this structure can effectively improve the conductivity of iron sulfide and suppress the volume expansion during the de-doping of potassium ions, so that it can stably and reversibly store potassium ions. An INDEPENDENT CLAIM is also included for preparing the egg yolk shell structure cathode material (I) comprising (i) dissolving ferric nitrate nonahydrate and polyvinylpyrrolidone (K30) in deionized water with ultrasonic stirring for 6-10 minutes to prepare mixed solution, completely drying and grinding into powder; (ii) transferring the ground powder to the crucible, placing the crucible in tubular furnace in hydrogen-argon mixed gas atm osphere, heating to 800-900 degrees C for 1-2 hours under heating rate of 5-8 degrees C/minute, cooling the tubular furnace to room temperature, collecting black foam-type product, which is three-dimensional graphene composite material modified by iron nanoparticles; (iii) adding the iron nanoparticle-modified three-dimensional graphene composite material and sulfur source precursor into hydrothermal reactor, adding deionized water, stirring and mixing well, sealing, placing the hydrothermal reactor in oven, and heating to certain temperature for many hours. and (iv) cooling the hydrothermal reaction to room temperature, collecting the precipitate, centrifugal washing the precipitate with deionized water and absolute ethanol for many times, drying the precipitate in vacuum oven to obtain three-dimensional graphene/iron sulfide cathode material with egg yolk shell structure.