## 1 Introduction  
The rapid development of wearable/flexible electronics has tremendously increased the attraction of flexible power supplies/devices that are lightweight and flexible [1, 2, 3]. Among various flexible power sources, fiber-shaped supercapacitors not only possess these superiorities of lightweight, small, and mechanical flexibility, but also can be easily woven into textiles, highlighting great advantages in the future flexible, portable, and wearable electronics field [4, 5, 6]. However, compared with lithium ion batteries or traditional supercapacitors, fiber-shaped supercapacitors display much lower specific capacitance and energy density, which impede their widespread application [7, 8]. As we know, the energy density of supercapacitors is proportional to its capacitance depending on the intrinsic charge storage capabilities of electrode materials [9, 10]. Therefore, much effort has been committed to exploiting new structural electrode materials to construct high electrochemical performance fiber-shaped supercapacitors for wearable/flexible electronic devices.  
For fiber-shaped supercapacitors, carbon-based materials are the most commonly utilized as electrodes because of their many characteristics including exceptional electric conductivity, large surface area, lightweight, low-cost, and chemical stability, as well as wide operating temperature range, especially graphene fibers [11, 12]. In 2011, [PERSON] and his coworkers exploited graphene oxides as a liquid crystal spinning solution, and first prepared graphene fibers by the wet-spinning method and chemical reduction [13]. Graphenefibers have been utilized extensively as flexible electrodes for wearable supercapacitors, exhibiting flexibility, lightweight, and representative double layer capacitor behavior. The charge-storage ability of the supercapacitors based on carbon materials is mainly dominated by the effective specific surface area. However, the graphene fibers exhibit graphite-like structures because of the strong \(\pi\)-\(\pi\) bonding existing in graphene nanosheets, which results in a low specific surface area and a poor wettability of the electrolyte [8; 14; 15]. The limited specific capacitance and poor energy density of the pure graphene fibers restrict further application in future wearable/flexible electronics [16; 17; 18]. Therefore, some materials with pseudocapacitive properties, for example, transition metal oxides [19; 20; 21; 22], metal sulfides [14; 23; 24; 25], and conducting polymers [9; 26; 27; 28], have been added into graphene fibers or other carbon materials to promote specific capacitance and energy density. Polyaniline is a potential candidate for the high theoretical specific pseudocapacitance and good electrical conductivity [29; 30]. Polyaniline is combined with graphene fibers, increasing the electroactive sites and providing a stable structure of composite fiber flexible electrodes in electrochemical measurement processes.  
In this research, polyaniline/graphene composite fibers (PANI/GFs) were constructed by the self-assembly method and chemical reduction processes. The synthesis processes are shown in Figure 1. The polyaniline obtained by chemical polymerization exists in graphene fibers, which could impede the aggregation of graphene nanosheets and guarantee the uniform distribution of PANI in the composite fibers. These fiber-shaped supercapacitors consisting of PANI/GFs display an outstanding areal specific capacitance of 370.2 mF cm\({}^{-2}\) and an excellent energy density of 12.9 \(\mu\)W h cm\({}^{-2}\) when the power density is up to 25.3 \(\mu\)W cm\({}^{-2}\) on PVA/H\({}_{2}\)SO\({}_{4}\) gel electrolyte. Graphene composite fibers exhibit potential advantages as fiber electrode for wearable energy storage systems, boosting the further application of graphene fibers in prospective flexible/wearable electronic devices.