A New View of Supercapacitors: Integrated Supercapacitors

Abstract

Until now, supercapacitors have been optimized in many ways to solve the abovementioned two main issues, such as the modification of existing materials, [5,6] the discovery of new materials, [7][8][9] the exploration of electrolytes, [10][11][12] the assembly of full supercapacitors, [13] the optimization of the voltage window etc. [14,15] Specifically, from the perspective of material development, RuO 2 is regarded as an ideal supercapacitor electrode material due to its high specific capacitance, but its high cost limits its practical application. [16,17] Thus, other nonnoble pseudocapacitive materials (for example, MnO 2 , [18] Fe 2 O 3 , [19] MoO 3 , [20] Nb 2 O 5 , [21] and VN [22] ) have attracted much attention. However, the poor electronic conductivity of most pseudocapacitor materials lead to their higher electrode resistances and lower power densities compared with those of EDLCs (Electrical Double Layer Capacitors) and electrolytic capacitors. [23] Very recently, 2D materials with high capacitances, such as MXenes, have been reported, but their main drawbacks are their complex synthetic processes and the use of highly toxic hydrofluoric acid (HF). [7,9] With regard to electrolytes, most researchers prefer aqueous electrolytes for their higher ionic concentration, lower resistance, lower cost, and better environmental-friendliness compared to those of organic electrolytes. [13,24,25] However, the limited potential window of aqueous supercapacitors, owing to the theoretical water splitting potential window of 1.23 V, is a challenge. To widen the potential window, supercapacitor electrodes must always be assembled into supercapacitor systems or so-called full supercapacitors, including symmetric supercapacitors, asymmetric supercapacitors, and hybrid supercapacitors. [4,5,13] To further enhance the voltage window of a single electrode or full supercapacitor, some methods have been adopted, including surface charge optimization, [14] electrode material modification, [15,26] electrolyte exploration, [5,10,24,27] and unique full supercapacitor system assemblies. [4,5,13] Although the above strategies have resulted in great progress for supercapacitors over the past few decades, the application of supercapacitors is still limited. Acquiring excellent performance while using simple methods is still a challenge. Thus, new strategies for the further development of supercapacitors are urgently needed. Herein, we propose a new view of the supercapacitor called the "integrated supercapacitor." As shown in the "supercapacitor tree" (Figure 1a), the integrated supercapacitor is a powerful strategy for integrating the traditional concepts of positive electrodes, negative electrodes, symmetric Charging times ranging from seconds to minutes with high power densities can be achieved by electrochemical capacitors in principle. Over the past few decades, the performance of supercapacitors has been greatly improved by the utilization of new materials, preparation of unique nanostructures, investigation of electrolytes, and ...

O/N Co‐Doped, Layered Porous Carbon with Mesoporosity up to 99 % for Ultrahigh‐Rate Capability Supercapacitors

“…Supercapacitors by virtue of high power density, long lifecycle, and environmental friendliness have always been the research hotspots in the field of electrochemical energy storage systems. [1][2][3] Although supercapacitors have been developed for several decades, the energy density is still much lower as compared to batteries and fuel cells. For instance, most of the carbon-based supercapacitors have an energy density of less than 10 Wh kg À 1 , which remains a big challenge for practical applications.…”

Regulating Voltage Window and Energy Density of Aqueous Asymmetric Supercapacitors by Pinecone‐Like Hollow Fe2O3/MnO2 Nano‐Heterostructure

“…Remarkably, the area of CV profile for Fe 2 O 3 /MnO 2 ‐3 NHs is far larger than that of MnO 2 , suggesting the capacitance of Fe 2 O 3 /MnO 2 ‐3 NHs electrode is higher than that of pure MnO 2 . Besides, the pure MnO 2 electrode has a polarization phenomenon when the voltage window increased to 1.0 V. In contrast, benefiting from the high oxygen evolution reaction overpotential and high redox electrochemical activity by the addition of Fe 2 O 3 , the voltage window of Fe 2 O 3 /MnO 2 ‐3 NHs electrode can reach to 1.2 V. These results indicate that the addition of Fe 2 O 3 conductive substrate can increase the capacitance performance and potential window of MnO 2 . The CV test at various scan rates indicates the stable working potential of Fe 2 O 3 /MnO 2 ‐3 NHs is 1.2 V (Figure b).…”

Morphology and crystal structure dependent pseudocapacitor performance of hydrated WO3 nanostructures

“…Highly efficient and nextgeneration energy storage devices are required to fulfill the desire of the smart civilization, for example long-lasting portable electronic devices, ecofriendly e-vehicles and so on. [1][2][3][4] Both batteries and supercapacitors are promising electrochemical energy storage devices. Remarkably, supercapacitors exhibit fascinating properties such as a fast charging-discharging rate, millions of life cycles and high power density compared to batteries.…”