**3. Optimization of graphene electrode-electrolyte for supercapacitors**

Carbon materials with large surface areas for charge storage are now the most researched materials. Despite these huge precise surface areas, the charges substantially deposited on the carbon electrodes. The deposition is somehow restricted by many factors, such as volume expansion, layer formation on the surface, surfaceto-volume ratio, etc. [72]. Therefore, an alternate electrode material is needed to enhance the performance of supercapacitor electrodes. Metal oxides and graphene is considered to be the exceptional electrode ingredients to enhance the performance of supercapacitors.

Electrolyte parameters, particularly specific capacitance and energy density are critical in determining the capacitive efficiency of electric double-layer capacitors (EDLCs). In particular, electrolytes with such a large electrochemical stability window (ESW) can provide superior specific capacitance as well as density, and that is why ionic liquid-based electrolytes have received a lot of attention. The quantity of ionic liquid (IL) is a significant parameter for controlling its viscosity, potential window, and ionic conductivity, which is represented in the EDLC working voltage and has yet to be well investigated [73]. A pseudocapacitor achieves charge aggregation by faradic reactions (redox reactions) of redox-active materials deposited on the electrodes or immersed in fluids. Because of their excellent redox characteristics, metal oxides have frequently been employed as cathodes for those deposited on the electrodes [74].

Graphene-based micro-supercapacitors on standard Xerox paper substrates were created in response to future demands for flexible, simple, and moderate energy storage devices. To enhance the overall performance of the device, the usage of redox-active species (iodine redox couple) was investigated. At 6.5 mA cm−3, the

*Perspective Chapter: Graphene Based Nanocomposites for Supercapacitor Electrodes DOI: http://dx.doi.org/10.5772/intechopen.106050*

smart printed device based on graphene composite had an amazing high volumetric capacitance of 29.6 mF cm−3 (volume of entire device). These electrodes contain redox-active potassium iodide. Surprisingly, the device demonstrated enhanced volumetric capacitance of 130 mF cm−3. In an H2 SO4 solution, the maximal density for a graphene +K device was determined to be 0.026 mWh cm−3 [75].

Surjit Sahoo et al. [76] described a unique supercapacitor device that uses 2D graphene sheets as electrode material. The markedly high energy storage and a porosity PVDF electrolyte incorporating TEABF4 as a solid-like piezo-polymer separator were used. When placed under stress, stresses ranging from 5 to 20 N, the porous PVDF film produced a voltage ranging from 4 to 11 V. The graphene polymer composite device had the highest particular device capacitance of 28.46 F g−1 (31.63 mF cm−2) as well a specific energy of 35.58 Wh kg−1, as well as a great power density of 7500 W kg−1. The above discussion shows that the optimum composition of electrolyte, as well as electrode configuration, is very important to obtain high capacity as well as cyclability.
