NOVELTY - A power storage device is manufactured by mixing raw materials comprising lithium to form 1st mixture, calcining 1st mixture, adding graphene oxide to 1st mixture to form 2nd mixture, and calcining 2nd mixture under e.g. inactive gas atmosphere to form positive-electrode active material (100) in which positive-electrode active material comprises core (101) comprising lithium metal oxide, and covering layer (102) which covers core and comprises structure where 1-10 graphene are stacked, and each graphene comprises hole (104) surrounded with covalently bonded carbon and oxygen atoms.    USE - Manufacture of power storage device for electronic devices e.g. digital cameras, video cameras, mobile phones, digital photo frames, portable game machines, portable information terminals, and audio reproducing devices. Can also be used for electric propulsion vehicles e.g. electric vehicles, hybrid vehicles, train vehicles, maintenance vehicles, carts, wheelchairs, and bicycles.    ADVANTAGE - The process improves electrical conductivity of positive-electrode active material and charge/discharge rate of power storage device, enables electrical charging/discharging at short time, has high current use efficiency and no conduction aid or extremely small amount of conduction aid, reduces cost, and minimizes secondary battery.    DETAILED DESCRIPTION - A power storage device is manufactured by mixing raw materials comprising lithium to form 1st mixture, calcining 1st mixture at 250-450 degrees C for 1-48 hours, adding graphene oxide to 1st mixture to form 2nd mixture, and calcining 2nd mixture at 500-800 degrees C for 1-48 hours under inactive gas atmosphere, reducing gas atmosphere, or vacuum to form positive-electrode active material in which positive-electrode active material comprises core comprising lithium metal oxide, and covering layer which covers core and comprises structure where 1-10 graphene are stacked, and each graphene comprises hole surrounded with covalently bonded carbon and oxygen atoms.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a positive-electrode active material.    Positive-electrode material (100)    Core (101)    Covering layer (102)    Hole (104)