Although there has been tremendous progress in exploring new configurations of zinc‐ion hybrid supercapacitors (Zn‐HSCs) recently, the much lower energy density, especially the much lower areal energy density compared with that of the rechargeable battery, is still the bottleneck, which is impeding their wide applications in wearable devices. Herein, the pre‐intercalation of Zn2+ which gives rise to a highly stable tunnel structure of ZnxMnO2 in nanowire form that are grown on flexible carbon cloth with a disruptively large mass loading of 12 mg cm−2 is reported. More interestingly, the ZnxMnO2 nanowires of tunnel structure enable an ultrahigh areal energy density and power density, when they are employed as the cathode in Zn‐HSCs. The achieved areal capacitance of up to 1745.8 mF cm−2 at 2 mA cm−2, and the remarkable areal energy density of 969.9 µWh cm−2 are comparable favorably with those of Zn‐ion batteries. When integrated into a quasi‐solid‐state device, they also endow outstanding mechanical flexibility. The truly battery‐level Zn‐HSCs are timely in filling up of the battery‐supercapacitor gap, and promise applications in the new generation flexible and wearable devices.
The development of novel electrochemical energy storage devices is a grand challenge. Here, an aqueous ammonium‐ion hybrid supercapacitor (A‐HSC), consisting of a layered δ‐MnO2 based cathode, an activated carbon cloth anode, and an aqueous (NH4)2SO4 electrolyte is developed. The aqueous A‐HSC demonstrates an ultrahigh areal capacitance of 1550 mF cm−2 with a wide voltage window of 2.0 V. An amenable peak areal energy density (861.2 μWh cm−2) and a decent capacitance retention (72.2% after 5000 cycles) are also achieved, surpassing traditional metal‐ion hybrid supercapacitors. Ex situ characterizations reveal that NH4+ intercalation/deintercalation in the layered δ‐MnO2 is accompanied by hydrogen bond formation/breaking. This work proposes a new paradigm for electrochemical energy storage.
As a new generation of Zn-ion storage systems, Zn-ion hybrid supercapacitors (ZHSCs) garner tremendous interests recently from researchers due to the perfect integration of batteries and supercapacitors. ZHSCs have excellent integration of high energy density and power density, which seamlessly bridges the gap between batteries and supercapacitors, becoming one of the most viable future options for large-scale equipment and portable electronic devices. However, the currently reported two configurations of ZHSCs and corresponding energy storage mechanisms still lack systematic analyses. Herein, this review will be prudently organized from the perspectives of design strategies, electrode configurations, energy storage mechanisms, recent advances in electrode materials, electrolyte behaviors and further applications (micro or flexible devices) of ZHSCs. The synthesis processes and electrochemical properties of well-designed Zn anodes, capacitor-type electrodes and novel Zn-ion battery-type cathodes are comprehensively discussed. Finally, a brief summary and outlook for the further development of ZHSCs are presented as well. This review will provide timely access for researchers to the recent works regarding ZHSCs.
Cobalt-doped Ni3S2 nanorod arrays have been prepared via a hydrothermal method. As a free-standing electrode, the Co-Ni3S2 demonstrates ultrahigh areal capacitance, affording the Co-Ni3S2//FeOOH hybrid supercapacitor a high energy density.
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