Graphene fibers (GF) have received great interest in wearable electronics applications because of their excellent mechanical flexibility and superior electrical conductivity. Herein, an all-in-one graphene and MnO2 composite hybrid supercapacitor fiber device has been developed. The unique coaxial design of this device facilitates large-scale production while avoiding the risk of short circuiting. The core backbone of the device consists of GF that not only provides mechanical stability but also ensures fast electron transfer during charge−discharge. The introduction of a MnO₂ (200 nm in length) hierarchical nanostructured film enhanced the pseudocapacitance dramatically compared to the graphene-only device in part because of the abundant number of active sites in contact with the poly(vinyl alcohol) (PVA)/H₃PO4 electrolyte.

The entire device exhibits outstanding mechanical strength as well as good electrocapacitive performance with a volumetric capacitance of 29.6 F cm⁻³ at 2 mv s⁻¹. The capacitance of the device did not fade under bending from 0° to 150°, while the capacitance retention of 93% was observed after 1000 cycles. These unique features make this device a promising candidate for applications in wearable fabric supercapacitors. Furthermore, the materials were applied to fabricate Li ion battery and the initial data is promising and more analysis is underway.