Highly electroconductive lightweight graphene fibers with high current-carrying capacity fabricated via sequential continuous electrothermal annealing

•Fast, energy-saving electrothermal annealing for healing defects of graphene fibers.•Sequential continuous Joule heating for developing next-generation conductors.•Large-scale production and systematic control of inner structure of graphene fibers.•Delineation of defect healing and graphitic structure development.•Investigation of deoxygenation and enhanced orientation of graphene fibers. The recent increase in demand for miniaturized electronics has necessitated the development of lightweight, narrow, and flexible channels with high current density as next-generation conductors. Despite the high electrical conductivity and current-carrying capacity (i.e., ampacity) of conventional metal conductors (e.g., copper and gold), their high mass density should be overcome for potential weight-critical applications. In this regard, defect-free graphene fibers (GFs) are excellent alternatives owing to their lightweight and high electroconductivity. In this study, GFs were electrothermally annealed at ~3000 K for a very short time (~50 s) via sequential continuous current injection. This treatment led to the carbonization and subsequent graphitization of the GFs, resulting in successful reparation of the structural disorder and crystalline defects of the GFs. This continuous process is advantageous for scaled production of highly electroconductive GFs. The resultant meter-scale GFs exhibit an electrical conductivity of 2721 S cm−1, maximum ampacity of 3.84 × 104 A cm−2, and specific current-carrying capacity of 4.67 × 104 A cm g−1, which are higher than the corresponding values of a commercial copper wire. This study provides a versatile and cost-effective technique for the development of advanced fibers and films as lightweight conductors for relevant applications.