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Lithium–sulfur (Li–S) battery is labeled as a promising high-energy-density battery system, but some inherent drawbacks of sulfur cathode materials using relatively complicated techniques impair the practical applications. Herein, an integrated approach is proposed to fabricate the high-performance rGO/VS4/S cathode composites through a simple one-step solvothermal method, where nano sulfur and VS4 particles are uniformly distributed on the conductive rGO matrix. rGO and sulfiphilic VS4 provide electron transfer skeleton and physical/chemical anchor for soluble lithium polysulfides (LiPS). Meanwhile, VS4 could also act as an electrochemical mediator to efficiently enhance the utilization and reversible conversion of LiPS. Correspondingly, the rGO/VS4/S composites maintain a high reversible capacity of 969 mAh/g at 0.2 C after 100 cycles, with a capacity retention rate of 82.3%. The capacity fade rate could lower to 0.0374% per cycle at 1 C. Moreover, capacity still sustains 795 mAh g–1 after 100 cycles in the relatively high-sulfur-loading battery (6.5 mg/cm2). Thus, the suggested method in configuring the sulfur-based composites is demonstrated a simple and efficient strategy to construct the high-performance Li–S batteries.

The selection and development of cathode of alkaline zinc batteries (AZBs) is still hindered and often leads to poor rate capability and short cycle life. Here, amorphous hollow nickel-cobalt-based sulfides nanocages with nanosheet arrays (AM-NCS) are designed and constructed with ZIF-67 as the self-template to exchange with Ni2+ and S2− by using a two-step ion exchange method. The synthesized AM-NCS possess the high specific capacity (160 mAh/g at 2 A/g), and the assembled battery has excellent rate performance (146 mAh/g reversible capacity at 5 A/g). The assembled device has excellent rate performance (155 mAh/g at 2 A/g) and long cycling stability (7000 cycles, 62.5% of initial capacity). The excellent electrochemical properties of the electrode materials are mainly attributed to the unique structure, in particular, polyhedron structure with hollow structure can improve the cyclic stability, and the amorphous structure can expose more reactive sites on the surfaces of nickel, cobalt and sulfur. This work provides a new strategy for the design and fabrication of high performance cathode materials for AZBs.

Aqueous zinc ion batteries (AZIBs) have broad prospects in many fields because of their high theoretical capacity, high hydrogen overpotential, low equilibrium potential, low cost and high safety. However, the surface chemical reactivity of cathode is usually limited by the utilization of active materials, resulting in insensitive edge position and unsatisfactory capacity. In this paper, a simple and convenient strategy is reported, in which the bimetallic phosphide nano-interfaces are constructed only by electrochemical high-voltage activation, so as to increase the electrode capacity of about 150 % (compared to the original NiCoP electrode). Under the combined action of water and oxygen, a coating of NiCo-OH nanosheet is formed on the NiCoP nano-wall, and the surfaces are rich in low-priced mixed state with remarkable reactivity and structural stability, which is theoretically confirmed by density functional theory (DFT). As a result, the 3D cathode has an ultra-high capacity of 544.9 mAh g

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.

The proposal of hybrid ion batteries, which can integrate the advantages of the single ion battery, opens up a new route for developing high-performance secondary batteries. Herein, we successfully constructed an aqueous hybrid battery comprised of polyanionic-type cathode material (Na

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.

NiCo2S4 nanosheet arrays have been successfully grown on carbon cloth via an easy hydrothermal way, which were then used to assemble asymmetric supercapacitors. The microstructures, the crystal structures and the electrochemical properties were carefully studied, and the NiCo2S4 nanosheet arrays exhibited impressive specific capacitance (SC) of 184.2 mAh/g at 1 A/g. The asymmetric supercapacitors (ASCs) with NiCo2S4 nanosheets as positive electrode demonstrated the energy density of 55.6 Wh/kg at 1.6 kW/kg. Furthermore, good cycle stability (93.72% after 5000 cycles) can be also possessed.

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.

High-performance energy storage systems are becoming essential to cope with the possible energy crisis in the future. Herein, unique hierarchical B-Co

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.

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.

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.

The electrode materials as the key component of supercapacitors have attracted considerable research interests, especially for nickel/cobalt based materials by virtue of their superior electrochemical performance with multiple oxidation states for richer redox reactions, abundant natural resources, lower prices and toxicity. There are many advanced electrodes based on the nickel/cobalt materials exploited for the application of supercapacitors, however, some controversial statements have induced some confusion. Herein, we refine the mechanism of energy storage for the nickel/cobalt based materials for supercapacitors and reclassify them into battery-type materials with the corresponding devices named as hybrid supercapacitors.

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.

Boron-doped NiCo2O4 (B-NiCo2O4) nanoarchitectures with rich oxygen vacancies have been rationally designed and synthesized on carbon fabrics via a conventional chemical reduction strategy. The B doping successfully realizes the introduction of oxygen vacancies, effectively accelerates ion and electron transport, increases the redox reactive sites, which endow the B-NiCo2O4 electrode with high specific capacity (799.9 C g−1 at 1 A g−1), outstanding rate capability (maintained about 75.1% at 20 A g−1) and impressive cyclic stability (about 94.7% retention of the initial capacity after 5000 cycles). The corresponding asymmetric supercapacitor assembled directly with B-NiCo2O4 electrodes exhibits a high energy density (77.7 Wh kg−1 at 2890.8 W kg−1) and a long lifespan (91% retention ratio after 5000 cycles). These remarkable properties indicate that the doping of hybrid atoms and the construction of defect engineering will provide a favorable reference for the performance promotion of the next-generation of energy storage devices.

Transition metal oxides (TMOs) with high specific capacities are considered to be alternative anodes for up-to-date lithium-ion batteries. However, the storage mechanism of TMOs-based anodes usually refers to conversion and alloying reactions, which cause the low initial Coulombic efficiency and fast capacity decay. Here, a new proof-of-concept nanocomposite of oxides-borides combined with reduced graphene oxides (CoO/Co2B/rGO) is proposed to regulate the storage mechanism of TMOs-based anodes. Cyclic voltammogram demonstrates the increasing proportion ranging from ~60% to 90% for the capacitive contribution at varied scan rates for this nanocomposite. As expected, the as-prepared CoO/Co2B/rGO nanocomposite exhibits an enhanced initial Coulombic efficiency together with cycling stability probably for the reduced Li+ diffusion contribution occurred in conversion and alloying reactions. These findings give a new insight into improving the lithium storage property of TMOs-based anodes for LIBs.