Non-aqueous energy storage devices using graphene nanosheets synthesized by green route

Abstract

In this paper we report the use of triethylene glycol reduced graphene oxide (TRGO) as an electrode material for non-aqueous energy storage devices such as supercapacitors and Li-ion batteries. TRGO based non–aqueous symmetric supercapacitor is constructed and shown to deliver maximum energy and power densities of 60.4 Wh kg–1 and 0.15 kW kg–1, respectively. More importantly, symmetric supercapacitor shows an extraordinary cycleability (5000 cycles) with over 80% of capacitance retention. In addition, Li-storage properties of TRGO are also evaluated in half-cell configuration (Li/TRGO) and shown to deliver a reversible capacity of ∼705 mAh g–1 with good cycleability at constant current density of 37 mA g–1. This result clearly suggests that green-synthesized graphene can be effectively used as a prospective electrode material for non-aqueous energy storage systems such as Li-ion batteries and supercapacitors

Symmetric Supercapacitor Based on Reduced Graphene Oxide in Non-Aqueous Electrolyte

“…As per energy storage mechanism, both anions (PF 6 − ) and cations (Li + ) are adsorbed on the graphene sheets during charging process, whereas the process is reversed during discharge. 5 It is obvious to notice that increasing sweep rate leads to a decrease in the net charge under the curve. At the high scan rates the surface of the active material (RGO) is only involved in the electrochemical reaction rather than the bulk, which results in a decrease in specific capacitance.…”

“…The obtained values are highly comparable to the previous reports. 5,16,17 Recently, Mhamane et al, reported the capacitance of 97 F g −1 at a current density of 0.1 A g −1 .…”

“…The observed values in the present study are comparatively higher than that of carbon based systems. 5,16,17 The cycling stability of symmetric RGO/RGO cell was subjected to galvanostatic charge-discharge cycling at a specific current density of 0.2 A g −1 (Fig. 3).…”

“…The specific capacitance measured in aqueous electrolytes is generally higher than in organic electrolyte. However, organic electrolytes are more attractive as they can withstand a higher operation voltage (up to 3 V) 5 than aqueous electrolyte (1.6 V for symmetric 6 and 2.0 V for asymmetric 7 supercapacitors). Compared with the batteries, the energy density of supercapacitors is often limited to less than 10 Wh kg −1 .…”

Graphene‐Based Energy Devices

“…Figure 3.34 and Table 3.4 summarize specific capacitances of common materials for supercapacitor applications [34]. Because of their merits of a large, open, flat layer with high surface area and excellent electronic transport properties, GNSs have been considered a promising electrode material for supercapacitors [34][35][36][37][38][39][40]. The capacitance of graphene can approach ∼200 F g −1 [34,35], even though the specific surface area of graphene is not high compared to activated carbon.…”