To solve balance problem between flexibility and energy density for graphene-based fiber electrodes,
graphene oxide (GO) with nanosheet size larger than 20 mm and Mn3O4 nanocrystals with a size of about
5 nm were used as assembled units, reduced graphene oxide (RGO)/Mn3O4 hybrid fibers with excellent
flexibility and high capacitance were prepared by a simple and scalable wet-spinning approach and
followed by treating in a solution of hydrazine hydrate, in which GO could be reduced into RGO, while
Mn3O4 nanocrystals were maintained after hydrazine vapor reduction treatment. A suitable amount of
Mn3O4 nanocrystals not only maintained the tensile strength and flexibility of the obtained fiber
electrode, but also obviously improved its capacitance. RGO/Mn3O4-30 fiber electrode showed a
maximum volumetric capacitance of 311 F cm 3 at a current density of 300 mA cm 3 on the basis of
maintaining the electrode good flexibility and mechanical strength. By intertwining two as-prepared
RGO/Mn3O4-30 flexible hybrid fiber electrodes, flexible symmetric all-solid-state fiber supercapacitor
was assembled by using PVA/H3PO4 as the gel electrolyte. The assembled device showed a maximum
volumetric capacitance of 45.5 F cm 3 at a current density of 50 mA cm 3, and remarkable flexibility and
mechanical property to tolerate long-term and repeated bending. Moreover, the assembled device
exhibited a maximum volumetric energy density of 4.05 mWh cm 3 and a maximum volumetric power
density of 268 mW cm 3. When three flexible symmetric all-solid-state fiber supercapacitors were
connected in series, the series device could be used to power a red light emission diode (LED) lamp after
being fully charged, demonstrating its potential application as an efficient energy storage component for
flexible electronics.