A Novel Flexible Hybrid Battery–Supercapacitor Based on a Self‐Assembled Vanadium‐Graphene Hydrogel

Abstract

A novel flexible hybrid battery–supercapacitor device is proposed consisting of high specific surface area electrodes paired with an electrolyte, which contains a redox species that can exist in more than two oxidation states. The two initially equal half‐cells of the device consist of a reduced graphene oxide hydrogel which encapsulates vanadium ions, synthesized with a single‐step method. During charge, the oxidation state of the vanadium ions changes, resulting in two half‐cells with different potentials which considerably increases the energy density. The achieved maximum capacity of more than 225 mAh g−1 is roughly eight times higher than that of comparable graphene hydrogel supercapacitors without vanadium content, but the potentiostatic charging time is only double. Operated as a supercapacitor, it retains 95% of the initial capacitance over 1000 cycles. As battery, the losses are more significant, retaining around 50% of the initial capacity. However, these losses during battery operation can be almost entirely restored by electric measures. The vanadium ion addition also improves the self‐discharge characteristics of the device. Moreover, the self‐discharge does not permanently damage the hybrid device since both half‐cells initially consist of the same vanadium graphene hydrogel and discharging resets it to initial conditions.

Facile Fabrication of Multivalent VOx/Graphene Nanocomposite Electrodes for High‐Energy‐Density Symmetric Supercapacitors

“…Among all types of vanadium oxides, V 2 O 5 has been studied the most for energy storage applications; [10][11][12][13][14][15] however, there are benefits to employing mixed-valence vanadium oxides (VO x ), since VO 2 and V 2 O 3 have higher electrical conductivities than V 2 O 5 [16] and the pre-existing multiple oxidation states are likely to provide a larger electrochemical active potential window. [17,18] For example, Yu et al reported a valence optimized VO x electro-oxidized from V 2 O 3 that increased its potential window from 0.5 V for pure V 2 O 3 to 0.8 V after their electro-oxidized modification. [19] Supercapacitors have emerged as one of the leading energy-storage technologies due to their short charge/discharge time and exceptional cycling stability; however, the state-of-the-art energy density is relatively low.…”

Research Progress of Graphene-Based Materials on Flexible Supercapacitors

“…Firstly, the force between the sheets is not uniform, so that some are strong and some are weak, resulting in the low overall strength of the material. Besides, the structural defect and disordered stack of the GHs lead to a poor electrical conductivity [134]. GAs not only have the advantages of graphene's high specific surface area and great conductivity, but also aerogel's characteristics of low density and high porosity [44].…”

“…As shown in Figure 13, 60 red light-emitting diodes (LED, 2.2 V) could be easily lit after charging for only 10 s in a single device filled only with ionic liquid electrolyte. The addition of transition metal oxide greatly improves the energy density of GHs [134]. Wang et al [139] prepared NiOOH nanosheets/GHs by solvothermal and hydrothermal mixing reactions.…”

Wood‐Derived Monolithic Ultrathick Porous Carbon Electrodes Filled with Reduced Graphene Oxide for High‐Performance Supercapacitors with Ultrahigh Areal Capacitances

“…However, the incorporation of pseudocapacitive materials would decelerate the charging and discharging rates, and diminish the stability of the devices. In addition, although graphene sheets are promising carbon materials for supercapacitors because of their high specific surface area, superior conductivity, and stable lattice structure, [39][40][41][42] their ease of stacking hinders the transport of ions and the infiltration of electrolytes into the electrode materials.…”