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Supercapacitors are playing a very relevant role in many applications due to their capability to supply high power density and long durability. However, there is a growing demand to increase their energy density, in gravimetric and volumetric basis. There are different strategies to increase supercapacitor performance by improving the active materials used in the electrodes, the type of electrolyte used or even the configuration employed in the cell. In this work, a combination of these strategies is presented with the use of different active materials, electrolytes, and symmetric vs. asymmetric configuration. The supercapacitor with asymmetric configuration using the graphene-doped carbon xerogel in the negative electrode and the manganese oxide in the positive electrode, along with the use of Na+-form Aquivion electrolyte membrane as solid electrolyte, seems to be a promising combination to obtain a substantial enhancement of both gravimetric and volumetric capacitance. Furthermore, the device presents great stability in a wide operational voltage window from 0 to 1.8 V and with a neutral pH polymer electrolyte which contributes to improve the performance, safety, and long cycle life of the device.

In this research work, we reported the synthesis of MnO2 by a simple co-precipitation technique and its use as electrode material for supercapacitors. Thus, hybrid supercapacitors with asymmetric configuration were constructed using a commercial activated carbon as the negative electrode, MnO2 and composites in the positive electrode, and Na+-form Aquivion electrolyte membrane as the separator and polymer electrolyte. The synergistic influence of MnO2 and carbon in the electrodes resulted in perfectly reversible charge storage processes at the positive electrode. As a result, the fabricated solid-state supercapacitors exhibited well rectangular voltammograms and a high specific capacitance of 130 F g ̶ 1 at 0.2 A g ̶ 1, as well as an energy density of 11.5 Wh kg ̶ 1 at a power density of 161 W kg ̶ 1. Moreover, this type of hybrid supercapacitor was able to achieve a long lifetime (i.e., 150 h at 1.6 V) for up to 10,000 cycles through a combination of galvanostatic charging/discharging, and floating conditions without compromising the capacitance stability. In addition, the NRT//MnO2 supercapacitor exhibited excellent voltage retention (self-discharge) of more than ∼74% at 48 h after charging in a high-voltage window of 1.6 V. These results suggest that the presented asymmetric solid-state configuration may be suitable for developing more efficient and sustainable energy storage devices.

For the development and optimization of solid-state symmetrical supercapacitors, herein, we propose using carbon-based electrodes and sodium- and lithium-form Aquivion electrolyte membranes, which serve as the separator and electrolyte. Carbon xerogels, synthesized using microwave-assisted sol-gel methodology, with designed and controlled properties were obtained as electrode materials. Commercial activated carbon (YP-50F, “Kuraray Europe” GmbH) was used as the active material for comparison. Notably, the developed solid-state symmetrical supercapacitors provide sufficiently high specific capacitances of 105–110 F g−1 at 0.2 A g−1, along with an energy density of 4.5 Wh kg−1 at 300 W kg−1, and a voltage window of 0–1.2 V in aqueous environments, also demonstrating an excellent cycling stability for up to 10,000 charge/discharge cycles. These results can demonstrate the potential applications of carbon xerogel as the active electrode material and cation exchange membrane as the electrolyte in the development of solid-state supercapacitor devices.