Active Material‐Free Continuous Carbon Nanotube Fibers with Unprecedented Enhancement of Physicochemical Properties for Fiber‐Type Solid‐State Supercapacitors

Fiber‐type solid‐state supercapacitors (FSSCs) are gaining traction as wearable energy storage devices, given their adaptability akin to traditional fibers. Carbon nanotube fibers (CNTFs) generated via a liquid crystalline (LC) wet‐spinning process demonstrate outstanding electrical conductivity, mechanical strength, and flexibility. However, their intrinsic “defect‐free” sp2 carbon surface restricts immediate FSSC application, limited by lower specific surface area and scant pseudocapacitive sites. This study develops LC‐spun CNTFs with inherent electrochemical activity, eliminating the need for post‐processing or additional active materials, a requirement typically essential in most previous research. This advancement arises from the wet‐spinning of functionalized CNTs from a LC solution with an exceptionally high concentration of 160 mg mL−1, facilitated by the manipulation of the LC phase transition range. The resultant CNTFs exhibit a refined internal structure, yielding an electrical conductivity of 1.9 MS m−1 and a mechanical strength of 0.93 GPa. Simultaneously, they demonstrate inherent electrical energy storage capabilities with a specific capacitance of 139.4 F g−1 and a volumetric capacitance of 192.4 F cm−3 at 0.5 A g−1. This innovation signifies a step forward in the potential for mass production without the burden of additional materials and steps. A high‐performance, fiber‐type, solid‐state supercapacitor is developed using functionalized CNTFs, which are fabricated by the wet‐spinning of their liquid crystal phase. These fibers not only possess exceptional physical properties but also exhibit inherent electrochemical activity. The active‐material‐free energy storage device in this study underscores the potential for efficient mass production of fiber‐type energy storage electrodes.