The main limitation of aqueous supercapacitors (SCs) lies in their narrow operating voltages, especially when compared with organic SCs. Fundamental understanding of factors relevant to the operating voltage helps providing guidance for the assembly of high-voltage aqueous SCs. In this regard, this concept analyzes the deciding factors for the operating voltage of aqueous SCs. Strategies applied to expand the operating voltage are summarized and discussed from the aspects of electrolyte, electrode, and asymmetric structure. Dynamic factors associated with water electrolysis and maximally using the available potential ranges of electrodes are particularly emphasized. Finally, other promising approaches that have not been explored and their challenges are also elaborated, hoping to provide more insights for the design of high-voltage aqueous SCs.

A facile solvothermal reduction strategy is demonstrated to introduce oxygen defects into ultrathin Co3O4 nanosheets (R–Co3O4), which function as an advanced cathode for Zn//Co batteries.

The exploration of high-energy anodes with good mechanical properties is highly attractive for flexible asymmetric supercapacitors (ASCs) but challenging. Owing to the excellent conductivity and superior mechanical flexibility, carbon fiber textile (CFT) holds great promise as a substrate/ current-collector for fabricating flexible electrodes. Yet, it is rarely used as a flexible active electrode in terms of its low electrochemical reactivity and small accessible area. In this work, an effective surface and structural modulation strategy is developed to directly tune CFT into a highly active anode for flexible ASCs by creating hierarchical pores and numerous pseudocapacitive oxygenic groups. Arising from large surface and increased active sites, the as-prepared activated porous CFT (APCFT) electrode not only achieves a large capacitance (1.2 F cm −2 at 4 mA cm −2 ) and fast kinetics but also shows satisfying cycling durability (no capacitance decay after 25 000 cycles). More importantly, an advanced flexible ASC device with an impressive energy density of 4.70 mWh cm −3 is successfully assembled by employing this APCFT as an anode, outperforming most recently reported ASC devices. This dual modification strategy may throw light on the rational design of new generation advanced carbon electrodes for high-performance flexible supercapacitors.

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