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Hybrid supercapacitors have the advantages of fast charging and discharging and long service life, which are an efficient and practical energy storage device. Therefore, the design of hybrid supercapacitors is the focus of current research. In this paper, the silver modified spinel NiCo2S4 nanorods (Ag2S-NiCo2S4/CF) are synthesized by an efficient and economical method, which has excellent electrochemical performance. The Ag2S-NiCo2S4/CF shows a high specific capacity of 179.7 mAh g−1 at current density of 1 A g−1, and excellent rate capability (capacitance retention of ~87% at 20 A g−1). The corresponding Ag2S-NiCo2S4/CF//AC/CF hybrid supercapacitor is assembled by Ag2S-NiCo2S4/CF as the positive electrode, which can provide an energy density of 35.978 Wh kg−1 at a high-power density of 800 W kg−1 and has significant cyclic stability (~80% of the initial capacitor after ~9600 cycles). Therefore, Ag2S-NiCo2S4/CF material is a promising electrode material that can be applied to hybrid supercapacitors.

In power storage technology, ion exchange is widely used to modify the electronic structures of electrode materials to stimulate their electrochemical properties. Here, we proposed a multistep ion exchange (cation exchange and anion exchange) strategy to synthesize amorphous Ni-Co-S and β-Co(OH)2 hybrid nanomaterials with a hollow polyhedron structures. The synergistic effects of different components and the remarkable superiorities of hollow structure endow Ni-Co-S/Co(OH)2 electrode with outstanding electrochemical performance, including ultra-high specific capacity (1440.0 C/g at 1 A/g), superior capacitance retention rate (79.1% retention at 20 A/g) and long operating lifespan (81.4% retention after 5000 cycles). Moreover, the corresponding hybrid supercapacitor enjoys a high energy density of 58.4 Wh/kg at the power density of 0.8 kW/kg, and a decent cyclability that the capacitances are maintained at 80.8% compared with the initial capacitance. This research presents a high-performance electrode material and provides a promising route for the construction of electrode materials for supercapacitors with both structural and component advantages.

Nano-polyhedral NiSe2/CoSe2 (Ni-Co-Se) with hollow architectures are synthesized by selenizing the precursors of Ni-Co bimetallic hydroxides that are directly derived from ZIF-67. The as-fabricated Ni-Co-Se electrodes exhibit high specific capacitance of 1668 F/g at 1 A/g accompanying with outstanding rate capability (about 82.8% retention of the initial capacity at 20 A/g). The corresponding Ni-Co-Se//AC all-solid-state hybrid supercapacitors are assembled by directly using the Ni-Co-Se on carbon fabric as the positive electrode, which deliver high energy density and power density (38.5 Wh/kg at 802.1 W/kg, 32.0 Wh/kg at 8008.8 W/kg), excellent cyclic stability (82.3% retention after 5000 cycle) and robust mechanical flexibility (no obvious attenuation at bending to different angles). This work will provide a new and smart route for constructing transition metal selenides for supercapacitor devices.

Dual-functional NiCo2S4 polyhedral architectures with outstanding electrochemical performance for supercapacitors and lithium-ion batteries (LIBs) have been rationally designed and successfully synthesized by a hydrothermal method. The as-synthesized NiCo2S4 electrode for supercapacitor exhibits an outstanding specific capacitance of 1298 F g−1 at 1 A g−1 and an excellent rate capability of ~80.4% at 20 A g−1. Besides, capacitance retention of 90.44% is realized after 8000 cycles. In addition, the NiCo2S4 as anode in LIBs delivers high initial charge/discharge capacities of 807.6 and 972.8 mAh g−1 at 0.5 C as well as good rate capability. In view of these points, this work provides a feasible pathway for assembling electrodes and devices with excellent electrochemical properties in the next generation energy storage applications.

High-performance aqueous zinc batteries are expected to be realized, rooting from component synergistic effects of the hierarchical composite electrode materials. Herein, hierarchical crystalline Ni–Co phosphide coated with amorphous phosphate nanoarrays (C-NiCoP@A-NiCoPO4) self-supporting on the Ni foam are constructed as cathode material of an aqueous zinc battery. In this unique core–shell structure, the hexagonal phosphide with high conductivity offers ultra-fast electronic transmission and amorphous phosphate with high stability, and open-framework provides more favorable ion diffusivity and a stable protective barrier. The synergistic effects of this intriguing core–shell structure endow the electrode material with outstanding reaction kinetics and structural stability, which is theoretically confirmed by density functional theory (DFT) calculations. As a result, the C-NiCoP@A-NiCoPO4 electrode exhibits a higher specific capacity of 350.6 mA h g−1 and excellent cyclic stability with 92.6% retention after 10 000 cycles. Moreover, the C-NiCoP@A-NiCoPO4 is coupled with Zn anode to assemble an aqueous pouch battery that delivers ultra-high energy density (626.33 W h kg−1 at 1.72 kW kg−1) with extraordinary rate performance (452.05 W h kg−1 at 33.56 kW kg−1). Moreover, the corresponding quasi-solid flexible battery with polyacrylamide hydrogel electrolyte exhibits favorable durability under frequent mechanical strains, which indicates the great promise of crystalline/amorphous hierarchical electrodes in the field of energy storage.

Hierarchical nanostructures with outstanding electrochemical properties and mechanical stability are ideal for constructing flexible hybrid supercapacitors. Herein, hierarchically hollow NiCo2S4@NiS nanostructures were designed and synthesized by sulfurizing the hierarchical NiCo double hydroxides (DHs) coated with nickel hydroxide nanostructures on carbon fabrics (NiCo-DHs@Ni(OH)2/CF), which trigger excellent electrochemical performances. The NiCo2S4@NiS/CF exhibits a high specific capacity of 1314.0 C g−1 at a current density of 1 A g−1, and maintains the rate performance at about 79.2% of the initial capacity at 30 A g−1. The hybrid supercapacitors of NiCo2S4@NiS//AC display a high energy density of 62.4 W h kg−1 at a power density of 800 W kg−1 with a remarkable cycling stability (96.2% of initial capacitance after 5000 cycles) and robust mechanical flexibility (no obvious decay of specific capacitance during various deformations). Consequently, NiCo2S4@NiS electrodes are expected to be a promising candidate for new smart energy storage devices with high security, stability and flexibility.

High-performance energy storage systems are becoming essential to cope with the possible energy crisis in the future. Herein, unique hierarchical B-Co4N have been reasonably designed and synthesized on Ni foam (NF) via a typical chemical reduction strategy. The successful realization of B-doping engineering effectively facilitates ion and electron transport, adding the electrochemically reactive sites, which endow the B-Co4N-20/NF electrode with high specific capacity (817.9 C g-1 at 1 A g-1), excellent rate capability (maintained about 90.9% at 10 A g-1) and cycling stability (about 93.06% retention of the initial capacity after 5000 cycles). The corresponding hybrid supercapacitor assembled with B-Co4N-20/NF electrodes has an energy density of 25.85 W h kg-1 at the power density of 800.2 W kg-1 and a long cycle life (98.59% retention ratio after 5000 cycles). These remarkable properties indicate that the doping of heteroatom and the construction of hierarchical structure will provide a favorable reference for the performance promotion of next-generation energy storage devices.

ZnCo2S4 nanoneedle clusters are uniformly grown as a core on foamed nickel and then are coated with Ni(OH)2 nanosheets as shell layers. The formed ZnCo2S4@Ni(OH)2 core–shell structures as electrode materials exhibit high specific capacitance (1193 C g−1 at 1 A g−1) and superior cycle rate performance (a capacity retention rate of 92% after 8000 cycles). The ZnCo2S4@Ni(OH)2//AC asymmetric supercapacitor composed of AC//NF as the negative electrode, ZnCo2S4@Ni(OH)2 as the positive electrode, porous glass fiber paper as the separator and 3 mol L−1 KOH as the electrolyte shows a specific capacitance of 215 F g−1 at 1 A g−1 with 70% capacitance retention and 100% coulombic efficiency even after 5000 cycles at a scan rate of 5 A g−1, evidencing the excellent energy storage capacitance and electrochemical performance. Besides, the ZnCo2S4@Ni(OH)2//AC device exhibits an exceptional energy density of ∼44 W h kg−1 at a power density of ∼0.83 kW kg−1.

Extensive exploratory works are dedicating to increase the energy density of aqueous asymmetric supercapacitors (AASCs), from the perspective of augmenting the specific capacitance and widening the operating voltage window. Herein, Mxene (V2C) derived unique accordion-like layered vanadium nitride coated by ultrathin amorphous carbon layer (L-VN@AC) is synthesized via a facile nitride strategy as negative electrode materials for AASC. Profiting from the distinctive layered structure inherited from V2C, the resultant L-VN@AC electrode exhibits a more remarkable areal capacitance (631.4 mF cm−2) and outstanding rate capability compared to the V2C precursor and commercial vanadium nitride (C-VN). Furthermore, a brand-new charge matching mechanism is proposed for the assembly of AASCs with capacitive-type (pseudocapacitance/electric double layer capacitance) electrode materials to soften the impact of energy density ascribed to the capacitance gap between the asymmetrical electrodes. Based on this charge matching mechanism, an optimized L-VN@AC//α-MnO2 AASC with 2.4 V operating voltage is assembled to achieve the enhancements in energy densities (597.5 μWh cm−2 at 2.4 mW cm−2 and 8.5 mWh cm−3 at 34.3 mW cm−3). It is believed that the design of high-performance L-VN@AC electrode materials and the proposal of balanced capacitance mechanism will provide new insights for the development of supercapacitors from two aspects of material synthesis and device assembly mechanism.

Energy storage devices with high security, stability and flexibility are desirable for newly smart wearable electronics. Herein, the moss-like nickel cobalt bimetallic phosphides (Ni-Co-P) nanosheet arrays on carbon fabrics are rationally designed and synthesized, which are directly treated as the electrodes to assemble highly flexible all-solid-state hybrid supercapacitors. The synthesized Ni-Co-P nanosheet arrays exhibit outstanding electrochemical performance and excellent stability owing to architectural advantages and compositional synergistic effect, which are further theoretically supported by calculations with density functional theory (DFT). The as-assembled hybrid supercapacitors deliver a high energy density of 48.4 Wh kg−1 at 811.2 W kg−1 accompanying a satisfactory cyclic stability (about 88.8 % retention after 8000 cycles). What's more, there is no obvious decline for the capacitance after bending 1,000 times under different bending states, implying excellent flexibility and mechanical stability of these bio-inspired nanosheet arrays. The outstanding mechanical stability and electrochemical performance demonstrate the promising potential of the hybrid supercapacitor as energy storage devices.