Capacitance of carbon-based electrical double-layer capacitors

Abstract

Experimental electrical double-layer capacitances of porous carbon electrodes fall below ideal values, thus limiting the practical energy densities of carbon-based electrical double-layer capacitors. Here we investigate the origin of this behaviour by measuring the electrical double-layer capacitance in one to five-layer graphene. We find that the capacitances are suppressed near neutrality, and are anomalously enhanced for thicknesses below a few layers. We attribute the first effect to quantum capacitance effects near the point of zero charge, and the second to correlations between electrons in the graphene sheet and ions in the electrolyte. The large capacitance values imply gravimetric energy storage densities in the single-layer graphene limit that are comparable to those of batteries. We anticipate that these results shed light on developing new theoretical models in understanding the electrical double-layer capacitance of carbon electrodes, and on opening up new strategies for improving the energy density of carbon-based capacitors.

Two-dimensional NiCo2O4nanosheet-coated three-dimensional graphene networks for high-rate, long-cycle-life supercapacitors

“…[1][2][3][4][5][6] There are mainly two types of supercapacitors, i.e. electric double-layer capacitors (EDLC) and pseudocapacitors.…”

“…electric double-layer capacitors (EDLC) and pseudocapacitors. The pseudocapacitor undergoes reversible redox reaction that occurs in the electrode materials, such as metal oxides (RuO 2 , MnO 2 , Co 3 O 4 , NiCo 2 O 4 , CoMoO 4 , etc.) [7][8][9][10][11][12][13][14][15][16] and metal hydroxides (Co(OH) 2 , Ni(OH) 2 , etc.…”

Highly densified carbon electrode materials towards practical supercapacitor devices

“…Besides, the specific gravimetric capacitance does not always increase with SSA due to many reasons [45]. For example, ultra-small pores, if present, are not accessible to ions in the electrolyte, whereas, these pores may be taken into consideration for the calculation of SSA.…”

“…A linear relationship between the specific capacitance and E-SSA has been obtained based on the experimental results for AC in various electrolytes. For carbons with very high SSAs such as graphene, other factors related to the space-charge capacitance, e.g., quantum capacitance, may play a more important role in the overall ion storage capability [45,[47][48][49].…”

“…Hence it is obvious that, for a specific active material, increasing the density without loss of gravimetric capacitance will directly contribute to the volumetric performance. However, there is usually a balance between the density and the SSA for carbon materials, and it is well known that the SSA has a direct correlation to the gravimetric capacitance within a certain range [45]. For example, AC electrodes have high SSAs but low stacking densities of around 0.3-0.6 g cm −3 , leading to a relatively low volumetric capacitance (80-120 F cm −3 in aqueous electrolyte and 40-80 F cm −3 in non-aqueous electrolyte) [39].…”