In this study, carbon nanorods (CNR) and graphene nanoribbons (GNR) derived from metal–organic frameworks (MOFs) were first prepared by solvothermal method. Then, Ni–Co layered double hydroxide (LDH)/CNR and LDH/GNR composite materials for supercapacitors were synthesized using a facile co-precipitation method. With the help of GNR, the Ni–Co LDH/GNR composite material showed great specific capacity (1765 F g⁻¹), rate performance (68% capacity retention when current density increased from 1 to 20 A g⁻¹) and cycling stability (83% capacity retention after 2000 charge–discharge cycles at 5 A g⁻¹). Furthermore, an asymmetric supercapacitor (ASC) with Ni–Co LDH/GNR as positive and activated carbon (AC) as negative electrodes was fabricated. The ASC device delivered a high energy density of 25.4 W h kg⁻¹ at power density of 749 W kg⁻¹ and exhibited excellent cycling stability (96% specific capacity retention after 5000 cycles).

Cauliflower-like NiCo₂S₄ nanoparticles (NPs) for use as battery-type materials have been synthesized via a simple one-step route solvothermal method with thioacetamide (TAA) as the sulfur source. The synthesis of the Ni–Co precursors and the S²⁻ anion exchange reactions occur at the same time, which is time-effective and cost-effective compared to other methods. The obtained NiCo₂S₄ NPs display very competitive electrochemical performance (a specific capacitance of 2480 F g⁻¹ is achieved at a current density of 0.5 A g⁻¹, excellent rate capability with 68% of the original capacitance remained at 10 A g⁻¹ and ideal cycle stability with 80% capacitance remained after 3000 cycles) with high mass-loading (5 mg cm⁻²). In addition, low-cost activated balsam pear pulp (ABPP) is developed as a capacitor-type carbon material for supercapacitors with ideal electrochemical performances. The asymmetric hybrid capacitors (AHCs) are further assembled into pouch cells using battery-type NiCo₂S₄ NPs as the positive electrode, capacitor-type ABPP as the negative electrode and flexible carbon papers as the current collector. The AHCs demonstrate high power density (3.52 kW kg⁻¹ at an energy density of 3.72 Wh kg⁻¹) and cycle stability (72.4% after 9000 cycles).

The soft-packed supercapacitor, assembled with Bi ₂ O ₃ and Ni(OH) ₂ , has an extremely high energy and power density. Connecting the two supercapacitors in series as a power source can light up the “SCU” LED sign and drive a tiny fan.

Graphene has attracted much attention since it was firstly stripped from graphite by two physicists in 2004, and the supercapacitor based on graphene has obtained wide attention and much investment as well. For practical applications of graphene-based supercapacitors, however, there are still many challenges to solve, for instance, to simplify the technological process, to lower the fabrication cost, and to improve the electrochemical performance. In this work, graphene/MnO₂ composites are prepared by a microwave sintering method, and we report here a relatively simple method for the supercapacitor packaging, i.e., dipping Ni-foam into a graphene/MnO₂ composite solution directly for a period of time to coat the active material on a current collector. It is found that the microwave reaction time has a significant effect on the microstructure of graphene/MnO₂ composites, and consequently, the electrochemical properties of the supercapacitors based on graphene/MnO₂ composites are strongly microstructure dependent. An appropriately longer microwave reaction time, namely, 15 min, facilitates a very dense and homogeneous microstructure of the graphene/MnO₂ composites, and thus, excellent electrochemical performance is achieved in the supercapacitor device, including a high specific capacitance of 296 F/g and a high capacitance retention of 93% after 3,000 times of charging/discharging cycles. PACS 81.05.ue; 78.67.Sc; 88.80.fh