Unzipped Carbon Nanotube/Graphene Hybrid Fiber with Less “Dead Volume” for Ultrahigh Volumetric Energy Density Supercapacitors

The development of 1D fiber‐shaped supercapacitors (SCs) with high volumetric energy density is of great significance for miniature wearable electronics, where limiting the device's volume is critical. In this study, a partially unzipped carbon nanotube/reduction graphene oxide (PUCNT/RGO) hybrid fiber with less “dead volume” and a well‐ordered porous structure is fabricated via wet spinning of a mixed partially unzipped oxidized carbon nanotube (PUOCNT)/GO solution and chemical reduction. The spinning solution is of low viscosity and high concentration, which can ensure smooth spinning while reducing the mass transfer during phase separation, thus lessen the “dead volume” derived from isolated pores. Moreover, PUOCNT with 1D and 2D hybrid nanoarchitecture, large specific surface area, and good water solubility can be a more effective spacer to inhibit the restacking of graphene oxide sheets while reducing the spacer itself and the large spacious voids formed “dead volume”. The all‐solid‐state SC assembled from the PUCNT/RGO hybrid fiber exhibits an excellent volumetric energy density of 8.63 mWh cm−3, exceeding the values of previously reported carbon‐based fibers. The findings may open a door for finely controlling the density and pore structure of graphene‐based fiber for applications in high volumetric energy storage via a scalable and efficient process. A partially unzipped carbon nanotube/graphene hybrid fiber is developed, featuring a well‐ordered porous structure and less “dead volume”. The performance of the constructed flexible supercapacitor is significantly improved, exhibiting an ultrahigh volumetric energy density of 8.63 mW h cm–3, long cycle stability over 20 000 cycles with 97.8% retention of initial specific capacitance, and excellent mechanical stability of 98.2% capacitance retention after 1000 times bending.