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Production cost, capacitance, and electrode materials safety are the key factors to be concerned about for supercapacitors. In this work, a type of carbon nanosheets was produced through the carbonization of tripotassium citrate monohydrate and nitric acidification. Subsequently, a well-designed manganese dioxide/carbon nanosheets composite was synthesized through hydrothermal treating. The carbon nanosheets served as the substrate for growing the manganese dioxide, regulating its distribution, and preventing it from inhomogeneous dimensions and severe agglomeration. Many manganese dioxide nanosheets grew vertically on the numerous functional groups generated on the surface of the carbon nanosheets during acidification. The synergistic combination of carbon nanosheets and manganese dioxide tailors the electrochemical performance of the composite, which benefits from the excellent conductivity and stability of carbon nanosheets. The carbon nanosheets derived from tripotassium citrate monohydrate are conducive to the remarkable performance of manganese dioxide/carbon nanosheets electrode. Finally, an asymmetric supercapacitor with active carbon as the cathode and manganese dioxide/carbon nanosheets as the anode was assembled, achieving an outstanding energy density of 54.68 Wh·kg−1 and remarkable power density of 6399.2 W·kg−1 superior to conventional lead-acid batteries. After 10000 charge-discharge cycles, the device retained 75.3% of the initial capacitance, showing good cycle stability. Two assembled asymmetric supercapacitors in series charged for 3 min could power a yellow light emitting diode with an operating voltage of 2 V for 2 min. This study may provide valuable insights for applying carbon materials and manganese dioxide in the energy storage field.

As an emerging energy storage device, supercapacitor is widely investigated owing to its excellent capability, quick charge-discharge and tremendous cycle life. The operation potential window, energy density and mass loading of supercapacitor must be taken into deep consideration for its practical application. In this work, an outstanding electrode based on CFF@V2O5 nanosheets was prepared. Then a free-standing asymmetric supercapacitor with CFF@V2O5 composite as positive electrode and CFF@AC as negative electrode was assembled. Owing to the functional groups produced on CFF after the activation, V2O5 nanosheets was immobilized. The composite exhibits remarkable specific capabilities of 1465 mF cm−2 (492 F g−1). The energy density of the assembled free-standing asymmetric supercapacitor achieves 0.928 mWh cm−3 when the power density is 17.5 mW cm−3. After 6000 charging-discharging cycles as under normal, bended and anti-bended conditions for respective 2000 cycles, the device retains 89.7% of the initial capacitance, exhibiting fascinating cycle stabilization. Finally, two devices linked series can lighten a LED of 1.8 V for 2 min after charging for 2.5 min, which is inspiring for the practical application and production of self-supporting asymmetric supercapacitors.

As a new energy-storage device, a supercapacitor has attracted great attention, but its low power density limits its wide application. The key to develop high-performance supercapacitors is to find...

Increasing requirements for wearable devices stimulate the development of flexible energy storage components. Herein, a flexible integrated electrode consisting of SnS2nanosheet arraysin situanchored on the functionalized carbon cloth was prepared via a facile one-step hydrothermal method. Through pretreatment of carbon cloth, rough morphology is appeared on the surface of carbon fiber, which is conducive to optimizing the accessible load of SnS2. The SnS2nanosheet arrays and the carbon fiber as conductive skeleton cooperate with each other to provide a highly open surface, leading to the enhancement in capacitance (194.4 mF cm-2) and the outstanding retention after long-term service (86.5% after 10 000 cycles). A quasi-solid-state asymmetric flexible supercapacitor was assembled to evaluate the practical application under various conditions, suggesting satisfactory electrochemical performance as a maximum energy density of 10.95μWh cm-2at the power density of 4.75 mW cm-2and mechanical stability under actual conditions.

As a typical flexible electrode substrate, carbon cloth (CC) has high flexibility but compromised capacitance performance. In this work, CuS nanoflake arrays with enhanced pseudocapacitance property are loaded on the surface of CC via a one-step solvothermal method. CuS nanoflakes provide the electroactive sites required for faradaic redox reaction, while the channels between the nanoflake arrays play a vital role to improve the efficiency of charges transportation. Benefit from the favorable microstructure, CuS/CC-4 demonstrates the specific capacity of 213.8 C g−1 at 0.49 A g−1 (436.5 mF cm−2 at 1 mA cm−2), and maintains 75.1% of initial capacitance after 5000 cycles. Furthermore, a quasi-solid-state asymmetric flexible supercapacitor (AFSC) is assembled with the voltage window of 1.6 V, which delivers the energy density of 0.027 mWh cm−2 and exhibits outstanding cycle stability of 86.4% after 5000 cycles at a high current density of 5 mA cm−2. This work provides insights into the integrated electrode containing the merits of flexibility, lightweight and satisfying electrochemical performance, and revealing its promising application prospects in flexible energy storage devices.

At present, it is still a challenge for developing hybrid supercapacitors with outstanding electrochemical performance. Herein, a step-by-step approach was tailored to fabricate a novel electrode material as nickel-vanadium layered double hydroxide (NiV-LDH)@Co2NiO4 nano-coral arrays anchored on nickel foam. Thanks to the three-dimensional interconnected nanostructure, the electrode fully immersed in electrolyte participates in faradaic redox reaction, which promotes the transfer of ions and charges, leading to the enhancement of electrochemical performance. The optimal NiV-LDH@Co2NiO4/NF (nickel foam) exhibits 1381.8 C g−1 at 1 A g−1, which is the best among the prepared samples (compared with NiV-LDH/NF and Co2NiO4/NF). Benefitting from the coral-like interconnect morphology, NiV-LDH@Co2NiO4/NF retains 79.8% of the initial capacity after 5000 cycles at 5 A g−1. Besides, NiV-LDH@Co2NiO4/NF and activated carbon (AC) act as positive and negative electrodes, assembling a hybrid asymmetric supercapacitor, which delivers an ideal energy density of 68.7 W h kg−1 at a power density of 878.6 W kg−1 and leaves 88.6% of specific capacity remaining after 5000 cycles. To evaluate the practical application of NiV-LDH@Co2NiO4/NF//AC, two devices are connected in series and acted as a continuous energy supply for a 2.2 V LED light.

Rapid developing flexible electronics, such as flexible screens, sensors and wearable devices, make them forward to invent portable and flexible energy storage systems. Flexible supercapacitors possess quick charge-discharge, high power density, environmentally friendly and flexible characteristics, which highly cater to the growing market demands. In supercapacitors, electrolyte is one of the key factors affecting their performance. Herein, we demonstrate that a self-assembly Mn3O4/carbon cloth (Mn3O4/CC) electrode is synthesized successfully by a two-step hydrothermal method. In a three electrodes system, the Mn3O4/CC electrode is tested in Na2SO4 and KOH respectively. The results reveal that Mn3O4/CC exhibits higher specific capacitance (555 mF cm−2 at 1 mA cm−2) and lower internal resistance in KOH. On the other hand, it expresses nearly no loss in the cycle stability test (99% retention after 2000 cycles) in Na2SO4. The all-solid-state asymmetric supercapacitor presents a maximum energy density reaching 25 μWh cm−2 with a power density of 0.64 mW cm−2. It also presents ultra-high flexibility (bending and twisting for 200 times) and superior cycling performance (99.3% after 2000 cycles). Hence, the Mn3O4/CC electrode is of great prospect in the application of flexible electronic devices.