A packaging for a flexible secondary battery that is wrapped around an outer surface of an electrode assembly of the flexible secondary battery, the packaging for a flexible secondary battery in a shape of a tube that is wrapped around the outer surface of the electrode assembly, the packaging for a flexible secondary battery comprising: a mechanical support layer; a reduced graphene oxide (rGO) layer disposed on the mechanical support layer and including a plurality of reduced graphene oxide sheets; a heat shrink layer disposed on the reduced graphene oxide layer; and a sealant layer disposed on the heat shrink layer, wherein reduced graphene oxide particles are stacked to form a reduced graphene oxide sheet; the plurality of reduced graphene oxide sheets in the reduced graphene oxide layer forms electrostatic interaction between adjacent reduced graphene oxide sheets, and forms the reduced graphene oxide layer; the reduced graphene oxide sheets form electrostatic interaction between the adjacent reduced graphene oxide sheets by medium of metal cation Li +, K +, Ag +, Mg 2+, Ca 2+, Cu 2+, Pb 2+, Co 2+, Al 3+, Cr 3+, Fe 3+, or two or more thereof, forming electrostatic interaction, including ionic bonding, with oxygen functional groups at the edge of the reduced graphene oxide particles. the packaging for a flexible secondary battery in a shape of a tube that is wrapped around the outer surface of the electrode assembly, the packaging for a flexible secondary battery comprising: a mechanical support layer; a reduced graphene oxide (rGO) layer disposed on the mechanical support layer and including a plurality of reduced graphene oxide sheets; a heat shrink layer disposed on the reduced graphene oxide layer; and a sealant layer disposed on the heat shrink layer, wherein reduced graphene oxide particles are stacked to form a reduced graphene oxide sheet; the plurality of reduced graphene oxide sheets in the reduced graphene oxide layer forms electrostatic interaction between adjacent reduced graphene oxide sheets, and forms the reduced graphene oxide layer; the reduced graphene oxide sheets form electrostatic interaction between the adjacent reduced graphene oxide sheets by medium of metal cation Li +, K +, Ag +, Mg 2+, Ca 2+, Cu 2+, Pb 2+, Co 2+, Al 3+, Cr 3+, Fe 3+, or two or more thereof, forming electrostatic interaction, including ionic bonding, with oxygen functional groups at the edge of the reduced graphene oxide particles. a mechanical support layer; a reduced graphene oxide (rGO) layer disposed on the mechanical support layer and including a plurality of reduced graphene oxide sheets; a heat shrink layer disposed on the reduced graphene oxide layer; and a sealant layer disposed on the heat shrink layer, wherein reduced graphene oxide particles are stacked to form a reduced graphene oxide sheet; the plurality of reduced graphene oxide sheets in the reduced graphene oxide layer forms electrostatic interaction between adjacent reduced graphene oxide sheets, and forms the reduced graphene oxide layer; the reduced graphene oxide sheets form electrostatic interaction between the adjacent reduced graphene oxide sheets by medium of metal cation Li +, K +, Ag +, Mg 2+, Ca 2+, Cu 2+, Pb 2+, Co 2+, Al 3+, Cr 3+, Fe 3+, or two or more thereof, forming electrostatic interaction, including ionic bonding, with oxygen functional groups at the edge of the reduced graphene oxide particles.