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Until now, crystalline NiCo2S4 and its composites have demonstrated improved performance in supercapacitor applications compared to their oxide analogues due to their relatively higher electrical conductivity and multifaceted redox reaction. However, amorphous phase materials have recently shown promise in electrochemical energy storage systems. This work reports on amorphous NiCo2S4 with the help of urea via the hydrothermal method. It was noted that urea not only aided the amorphous formation but also served as a nitrogen precursor. In comparison, amorphous NiCo2S4 demonstrated a higher nitrogen atom% of 5.9 compared to 4.49 for crystalline NiCo2S4. Furthermore, the amorphous NiCo2S4 electrode exhibited superior electrochemical performance, with a specific capacitance of ~3506 F g−1, which was higher than the cNCS electrode's specific capacitance of ~2185 F g−1 at 2 A g−1. Additionally, aNCS in a two-electrode asymmetric supercapacitor exhibited a specific capacitance and an energy density of ~196 F g−1 and 56 Wh kg−1, respectively. [ABSTRACT FROM AUTHOR]

In this study, a hierarchical heterostructure composed of NiCo 2 S 4 bound to a carbon substrate (NiCo 2 S 4 /CNs) was created. The heterostructure enhances OH− adsorption on Ni and Co active sites and boosts electronic conductivity. Ex-situ XRD reveals mutual transformations of sulfides and hydroxyl oxides during charging/discharging in alkaline solution. DFT confirms that the heterostructure facilitates faster, more efficient redox reactions by enhancing conductivity and OH− adsorption/desorption on active sites. This architectural approach stabilizes charge statuses at the interface, prevents electrode structure collapse, and leads to notable electrochemical performance. [Display omitted] • A hierarchical heterostructure of NiCo 2 S 4 anchored onto a carbon substrate is successfully fabricated. • The innovative design enhances the adsorption of OH− on independent active sites of Ni and Co. • Ex-situ XRD confirms the mutual transformation of sulfides, hydroxides, and hydroxyl oxides. • NiCo 2 S 4 /CNs electrode exhibits excellent specific capacity and high energy density. To improve the low energy density, low conductivity, and poor cycling stability of NiCo 2 S 4 in supercapacitors, a two-step hydrothermal method was used to prepare a composite material of NiCo 2 S 4 and carbon nanosheets (NiCo 2 S 4 /CNs). The electrochemical tests revealed a high specific capacitance of 1576 F g−1 at 1 A/g for the composite, and the NiCo 2 S 4 /CNs//AC asymmetric supercapacitor showed a energy density of 49.7 Wh kg−1 at 818 W kg−1. This study confirmed the phase transformation of NiCo 2 S 4 during charge/discharge in alkaline solution through ex-situ X-ray diffraction (ex-situ XRD) for the first time, and proposed a potential reaction pathway. Moreover, Density Functional Theory (DFT) confirmed that the NiCo 2 S 4 /CNs heterostructure enhances OH− adsorption/desorption on Ni and Co active sites and improves electronic conductivity. In conclusion, this study advances the application of transition metal sulfide in high-performance energy storage. [ABSTRACT FROM AUTHOR]

One‐step colloidal synthetic route was adopted to in‐situ grow monodispersed NiCo2S4 nanoparticles (NPs) on nickel foam (NF) from metallic salts with benzyl disulfide in the media of oleylamine and octadecene. Owing to the favorable dispersion and considerable redox activity of NiCo2S4 along with tight and binder‐free connection with NF, the obtained battery‐type supercapacitor delivered a specific capacitance of 1790.8 F g−1 at 1 A g−1 via a three‐electrode system. Simultaneously, it just degraded 40 % at 20 A g−1 and maintained 86.8 % of initial specific capacitance (C0) after 2000 cyclic trials at 10 A g−1. When the NiCo2S4 NPs were assembled with active carbon (AC) forming an asymmetric capacitor device of NiCo2S4 NPs//AC, it delivered an energy density (E) of 48.7 W h kg−1 at a power density (P) of 161.1 W kg−1, and kept 21.9 W h kg−1 at a high P of 8.05 kW kg−1. Meanwhile, the capacitor manifested preeminent cycling life (C=94.5 % C0 after 5000 cyclic trials) at 5 A g−1. The in‐situ grown NiCo2S4 NPs on NF without any binder exhibited high performance in energy storage, providing a feasible way to improve the electrochemical performance of the electrode materials. [ABSTRACT FROM AUTHOR]

Transition bimetallic sulfides exhibit high capacity and outstanding chemical performance in supercapacitors due to their abundant electrochemical active sites and conductivity. In this paper, NiCo2S4 with an obvious core–shell nanosphere structure was prepared by adjusting the amount of thiourea by a one-step hydrothermal method. This special core–shell structure of the NiCo2S4 material can provide more active sites to make it exhibit better electrochemical performance. The electrochemical performance test results show that the NiCo2S4 material prepared with 16 mmol thiourea can reach 1224.0 F g−1 at the current density of 1 A g−1, and maintain 88.74% capacitance even at 10 A g−1. In addition, with the NiCo2S4 as the positive electrode and activated carbon as the negative electrode, the supercapacitor (NiCoS3//AC) can achieve the specific capacitance of 121.9 F g−1 when the current density is 1 A g−1. At a power density of 614 W kg−1, the energy density reaches 38.1 Wh kg−1. The results show that the microstructure of the material is closely related to the amount of thiourea added, and that only appropriate degree of vulcanization is helpful for the formation of core–shell-like NiCo2S4 with excellent performance. NiCo2S4 material with its unique core–shell structure makes it exhibit a better energy storage performance. [ABSTRACT FROM AUTHOR]

Converting biowaste into carbon-based supercapacitor materials provides a new solution for high-performance and environmentally friendly energy storage applications. Herein, the hierarchical PAC/NiCo2S4 composite structure was fabricated through the combination of activation and sulfuration treatments. The PAC/NiCo2S4 electrode garnered advantages from its hierarchical structure and hollow architecture, resulting in a notable specific capacitance (1217.2 F g−1 at 1.25 A g−1) and superior cycling stability. Moreover, a novel all-solid-state asymmetric supercapacitor (ASC) was successfully constructed, utilizing PAC/NiCo2S4 as the cathode and PAC as the anode. The resultant device exhibited exceptionally high energy (49.7 Wh kg−1) and power density (4785.5 W kg−1), indicating the potential of this biomass-derived, hierarchical PAC/NiCo2S4 composite structure for employment in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

Throughout the evolution of supercapacitors, binary transition metal sulfides have been extensively researched for their potential as electrode materials. Here, NSAC-NiCo 2 S 4 composites are prepared by in-situ growing NiCo 2 S 4 nanosphere on N, S co-doped activated carbon (NSAC) using a simple solvothermal way. The optimized NSAC-NiCo 2 S 4 composite inherits the NSAC's huge specific surface area, hierarchical porous structure, and high electronic conductivity, along with the excellent capacitive performance of NiCo 2 S 4. This combination effectively reduces contact resistance and enhances the transfer rate. Calculations based on the density functional theory further indicate that synergistic interactions between NiCo 2 S 4 and NSAC in the composite lower the OH− adsorption energy and release more active electrons. This enhancement facilitates the electrochemical reaction kinetics in supercapacitors. The as-fabricated NSAC-NiCo 2 S 4 -2 electrode possesses a remarkable specific capacitance (762 F g−1) at 1 A g−1 and exhibits a minimal charge transfer resistance (0.28 Ω). Furthermore, an asymmetric supercapacitor (positive electrode: NSAC-NiCo 2 S 4 -2; negative electrode: NSAC), achieves an impressive energy density of 36.6 Wh kg−1 at a power density of 400.0 W kg−1. It also exhibits exceptional cycling stability, maintaining 86.2 % of its capacity after 10,000 cycles. These excellent results further highlight the great potential of the obtained NSAC-NiCo 2 S 4 composites for use in energy reserve systems. [Display omitted] • Spherical-like structure NiCo 2 S 4 in-situ growing on N, S co-doped activated carbon (NSAC). • NSAC-NiCo 2 S 4 -2 composites have fast electron transport and high specific capacitance performance. • NSAC-NiCo 2 S 4 -2//NSAC device exhibits high energy density and excellent cycling stability. [ABSTRACT FROM AUTHOR]

• The simple preparation of ZnCo 2 S 4 with double hollow morphology by two-part hydrothermal method has excellent performance. • The synthesis of ZnCo 2 S 4 /Ti 3 C 2 T x and ZnCo 2 P 4 /Ti 3 C 2 T x via the electrostatic self-assembly method was successfully accomplished, and their subsequent assembly with AC led to the formation of LIC. • The specific capacitance of ZnCo 2 S 4 /Ti 3 C 2 T x is 1563 C·g−1, which exceeds that of ZnCo 2 P 4 /Ti 3 C 2 T x (936 C·g−1) and pure Ti 3 C 2 T x (289 C·g−1). • Lithium-ion capacitors based on ZnCo 2 S 4 /Ti 3 C 2 T x provide an energy density of 136.25 Wh kg−1 at a specific power of 337.10 W kg−1. Lithium-ion capacitors (LICs) represent a novel energy storage solution, merging the high energy storage capacity of lithium-ion batteries with the adequate power density of supercapacitors. However, the electrochemical performance of lithium-ion capacitors is notably constrained by the inherent imbalance between the charge storage mechanisms and electrochemical reaction dynamics of their anodes and cathodes. In this study, a dual-shell hollow structured ZnCo 2 S 4 was prepared via a two-step hydrothermal method and compared with spherical ZnCo 2 P 4 prepared by calcination. Subsequently, they were respectively anchored onto two-dimensional Ti 3 C 2 T x nanosheets, which possess abundant surface functional groups, through electrostatic adsorption, forming layered semi-encapsulated framework structures. The introduction of MXene significantly enhances the conductivity of the material, restricts the expansion of ZnCo 2 S 4 and ZnCo 2 P 4 during the Li+ insertion/extraction process, and inhibits their aggregation. Under a three-electrode configuration, ZnCo 2 S 4 /Ti 3 C 2 T x exhibits excellent rate performance (1004 C·g−1 at 10 A·g−1) and cycling stability (95 % capacity retention after 5000 cycles at 2 A·g−1). The discharge capacity of the ZnCo 2 S 4 /Ti 3 C 2 T x LIB is up to 1360 mAh·g−1 at 0.1 A·g−1, and the discharge capacity of the ZnCo 2 P 4 /Ti 3 C 2 T x LIB is 1121 mAh·g−1 at 0.1 A·g−1. As an anode material for LIC, ZnCo 2 S 4 /Ti 3 C 2 T x demonstrates excellent specific capacitance and rate performance (105 F·g−1 at 0.5 A·g−1). At a power density of 337.10 W·kg−1, ZnCo 2 S 4 /Ti 3 C 2 T x //AC LIC exhibits a significant energy density of 136.25 Wh·kg−1. At a current density of 2 A·g−1, ZnCo 2 S 4 /Ti 3 C 2 T x //AC LIC retains 89 % of its capacity after 5000 charge-discharge cycles, demonstrating excellent stability for practical applications. ZnCo 2 P 4 /Ti 3 C 2 T x //AC LIC exhibits an energy density of 45.20 Wh·kg−1 at a power density of 623.07 W·kg−1, and after 5000 cycles at 2 A·g−1, its capacity retention rate reaches 80 %. These findings suggest that ZnCo 2 S 4 /Ti 3 C 2 T x and ZnCo 2 P 4 /Ti 3 C 2 T x composites are promising anode materials for LICs. [ABSTRACT FROM AUTHOR]

Transition-metal sulfides exaggerate higher theoretical capacities and were considered a type of prospective nanomaterials for energy storage; their inherent weaker conductivities and lower electrochemical active sites limited the commercial applications of the electrodes. The sheet-like nickel cobalt sulfide nanoparticles with richer sulfur vacancies were fabricated by a two-step hydrothermal technique. The sheet-like nanoparticles self-combination by ultrathin nanoparticles brought active electrodes entirely contacted with the electrolytes, benefiting ion diffusion and charges/discharges. Nevertheless, defect engineers of sulfur vacancy at the atomic level raise the intrinsic conductivities and improve the active sites for energy storage functions. As a result, the gained sulfur-deficient NiCo2S4 nanosheets consist of good specific capacitances of 971 F g−1 at 2 A g−1 and an excellent cycle span, retaining 88.7% of the initial capacitance over 3500 cyclings. Moreover, the values of capacitance results exhibited that the fulfilling characteristic of the sample was a combination of the hydrothermal procedure and the surface capacitances behavior. This novel investigation proposes a new perspective to importantly improve the electrochemical performances of the electrode by the absolute engineering of defects and morphologies in the supercapacitor field. [ABSTRACT FROM AUTHOR]

In this work, NiCo2S4–graphene hybrids (NCS@G) with high electrochemical performance were prepared using a hydrothermal method. The response surface methodology (RSM), along with a central composite design (CCD), was used to investigate the effect of independent variables (G/NCS, hydrothermal time, and S/Ni) on the specific capacitances of the NCS@G/Ni composite electrodes. RSM analysis revealed that the developed quadratic model with regression coefficient values of more than 0.95 could be well adapted to represent experimental results. Optimized preparation conditions for NCS@G were G/NCS = 6.0%, hydrothermal time = 10.0, and S/Ni = 6.0 of NCS@G (111) sample. The maximum specific capacitance of NCS@G (111)/Ni fabricated at the optimal condition is about 216% higher than the best result obtained using the conventional experimental method. The enhanced capacitive performance of the NCS@G (111) sample can be attributed to the synergistic effect between NCS nanoparticles and graphene, which has the meso/macropores conductive network and low diffusion resistance. Notably, the NCS@G (111) could not only provide numerous reaction sites but also prevent the restacking of graphene layers. Furthermore, a supercapattery cell was fabricated with an (G + AC)/Ni anode, a NCS@G (111)/Ni cathode, and a carboxymethyl cellulose–potassium hydroxide (CMC-KOH) gel electrolyte. The NCS@G (111)//(G + AC) demonstrates an outstanding energy density of 80 Wh kg−1 at a power density of 4 kW kg−1, and a good cycling performance of 75% after 5000 cycles at 2 A g−1. Applying the synthesis strategy of RSM endows remarkable capacitive performance of the hybrid materials, providing an economical pathway to design promising composite electrode material and fabricate high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • The bimetallic sulfides and electrospun carbon nanofibers are integrated. • The high conductivity and active sites promote adsorption and catalytic conversion. • The cathode with hierarchical structure shows excellent electrochemical performance. As a new generation of energy storage systems, lithium-sulfur batteries (LSBs) with high energy density up to 2600 Wh kg−1 present broad development prospects. However, their practical applications are faced with the problems of slow redox kinetics as well as shuttle effect of lithium polysulfides (LiPSs). Herein, we have developed a structure and function integrated cathode of bimetallic sulfides/electrospun carbon nanofibers. The rational designed cathode with hierarchical structure can achieve the physical confinement of polysulfide and accommodate sulfur volume expansion/contraction throughout the lithiation/delithiation cycle to alleviate the impact of volume expansion during conversion process of sulfur. And bimetallic sulfides with high electron conductivity and abundant chemical active sites not only can provide fast transmission paths for electrons and ions but also anchor LiPSs through Lewis acid-base interactions suppressing shuttle effect efficiently, finally reducing polarization and overpotential. Therefore, the well-designed sulfur-host cathode shows remarkable reversible capacity of 908.6 mAh g−1 at 2C and still has specific capacity of 680.1 mAh g−1 after 500 cycles at 1C, further demonstrating practicality feasibility of this design. [ABSTRACT FROM AUTHOR]

A 3D flower bud-like P, W co-doped NiCo 2 S 4 @MoS 2 (P, W-NCS@MS) composites grown on carbon cloth transforming from the nanoneedle-like precursors (P, W-NCH) by hydrothermal method as a high-performance electrode for asymmetric supercapacitor. [Display omitted] • A novel 3D flower bud-like P, W co-doped NiCo 2 S 4 @MoS 2 composites is designed. • Heteroatoms P and W dope directly in sulfide by introducing phosphotungstic acid. • Hierarchical interfaces of MoS 2 and NiCo 2 S 4 accelerate the ions diffusion process. • The ASC device achieves an ultrahigh energy density of 65.1 Wh kg−1 at 400 W kg−1. • The constructed ASC device can drive a digital watch for over 3 h. Engineering binary transitional metal sulfides (BTMSs)-based electrode materials with a rationally designed constituent architecture is a viable strategy for improving their rate capability and electrochemical durability, which provides a possibility for their application in supercapacitors (SCs). Herein, a novel three-dimensional (3D) flower bud-like phosphorus and tungsten co-doped NiCo 2 S 4 and MoS 2 composites (P, W-NCS@MS) is prepared on conductive carbon cloth using the hydrothermal method. The effects of P, W-doping, or MoS 2 -combination on the morphology, structure and electrochemical properties of NiCo 2 S 4 -based electrode materials are systematically studied. The designed P, W-NCS@MS achieves a high specific capacity of 1250C g−1 at 1 A g−1 and a satisfactory capacity retention of 80 % after 10,000 cycles. In addition, the asymmetric supercapacitor (ASC) constructed through P, W-NCS@MS and activated carbon electrodes delivers a high energy density of 65.0 Wh kg−1 at the power density of 400 W kg−1 and shows satisfactory cycling stability of 85 % capacitance retention after 20,000 cycles. Notably, the assembled ASC device successfully powered electronic devices in a serial circuit, highlighting its prospective applications in energy storage. This work offers a viable design approach for heteroatom doping and hierarchical interface structures in composite electrode materials toward high-performance SCs. [ABSTRACT FROM AUTHOR]

The electrode materials, which exhibit improved electrochemical characteristics, have broad applications in high-capacity and high-power-density storage devices like supercapacitors. This research investigates the synthesis, electrochemical performance, and characterization of novel nanostructures comprised of molybdenum-doped nickel cobalt sulfide (Mo-NiCo 2 S 4 NSs) as active electrode materials. For the first time, Mo-NiCo 2 S 4 nanostructures synthesized via a one-step hydrothermal method demonstrate high efficiency as supercapacitor materials, showcasing their potential for supercapacitor applications. To examine the physical and chemical characteristics of the synthesized Mo-NiCo 2 S 4 nanostructures, X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) analyses were employed. Furthermore, the electrochemical efficacy of novel electrode materials was investigated using three electrodes configuration, aiming for superior performance in supercapacitor applications. Moreover, the collaborative effect of Mo-NiCo 2 S 4 NSs was examined via cyclic voltammogram (CV), galvanostatic charge-discharge (GCD) curves, and electrochemical impedance spectroscopy (EIS). The cotton-like modified morphology observed via SEM revealed an increase in redox-active sites, thereby enhancing the energy storage capacity of the electrode material. The optimized sample (5 % Mo-NiCo 2 S 4 NSs) demonstrated a specific capacitance of 1740 F g−1 at a current density of 4 A g−1. Additionally, the optimized electrode displayed notable energy density (60.4 WhKg−1) and power density (500 Wkg-1). The modified cotton-like morphology of the optimized sample exhibited superior electrochemical performance compared to the NiCo 2 S 4 NSs. This study suggests that Mo-NiCo 2 S 4 nanostructures hold great promise as electrode materials for future supercapacitors in energy storage systems. • For the first time , molybdenum-doped nickel cobalt sulfide nanostructures (Mo-NiCo 2 S 4 NSs) were synthesized. • 5 % Mo-NiCo 2 S 4 NSs exhibits an outstanding specific capacitance of 1740 Fg-1. • Remarkable energy density of 60.4 WhKg−1 and power density of 500 Wkg-1 achieved for the optimized sample. • This research provides a way for NiCo 2 S 4 NSs to be used in energy storage applications. [ABSTRACT FROM AUTHOR]

MXene, an emerging 2D material, has aroused great concern in the field of supercapacitors owing to its charming properties. However, the relatively low specific capacitance of pristine MXene is unsatisfactory, which is caused by the restacking issue of MXene nanosheets. In this paper, a facile and cost-effective electrostatic self-assembly followed by hydrothermal method was adopted to prepare NiCo2S4 decorated multilayer MXene nanosheets (MXene/NiCo2S4). The introduced NiCo2S4 effectively alleviates the self-restacking of MXene nanosheet and facilitates ion accessibility. Hence, the as-prepared MXene/NiCo2S4 electrode displays a maximum specific capacitance of 1211.1 F g−1 at 1 A g−1, surpassing the NiCo2S4 electrode (938.4 F g−1 at 1 A g−1) and pure MXene electrode (84.2 F g−1 at 1 A g−1). The assembled asymmetrical supercapacitor utilizing hybrid MXene/NiCo2S4 and RGO delivers a high energy density of 38.7 Wh kg−1 and high power density of 6137 W kg−1. This work can provide a reliable reference for the synthesis of hybrid MXene/sulfide electrodes with ideal electrochemical performance. [ABSTRACT FROM AUTHOR]

Flower‐like NiCo2S4@biomass‐graded porous carbon (NiCo2S4@BGPC) material was successfully prepared using a simple hydrothermal method and the pseudocapacitive performance was investigated. The results showed that the composite had good capacitive behavior and electrochemical activity due to the structural synergy of the porous carbon and flower‐like material. In this composite, the flower‐like NiCo2S4 had a large contact area with the electrolyte solution, providing many active sites for pseudocapacitive reactions. Meanwhile, the introduction of the porous carbon skeleton further ensured the structural stability of the composite's conductive network. In summary, the flower‐like NiCo2S4@BGPC material showed the high specific capacitance of 1322.5 F g−1 at the current density of 1 A g−1 and excellent coulombic efficiency (96.8 % after 1000 cycles at 10 A g−1). However, it has poor cycling stability (77 % of the initial specific capacitance after 1000 cycles at 10 A g−1), which can be attributed to blockage of the pore structure due to volume expansion during the redox process. In two‐electrode system tests, both NiCo2S4@BGPC//NiCo2S4@BGPC symmetrical supercapacitor and NiCo2S4@BGPC//AC asymmetrical supercapacitor showed good capacitance performance and cycling performance, implying potential applications of NiCo2S4@BGPC in commercial electrochemical energy storage. [ABSTRACT FROM AUTHOR]

• The hierarchical hollow NiCo 2 S 4 /MXene/NC microspheres is constructed via a dual-template strategy. • The eletrode displays impressive electrochemical properties and cyclic stability. • Hybrid energy storage behavior both with pseudocapacitance and diffusion-controlled contributions is indicated for the electrode. • The incoperation of MXene increases the ion diffusion channels and the electronic conductivity of electrodes. A multi-step strategy was rationally designed to fabricate hierarchical hollow core–shell microspheres of NiCo 2 S 4 MXene/N-doped carbon (NiCo 2 S 4 /MXene/NC) using dual templates of the polyethylene microspheres and metal–organic framework material of ZIF-67. The integration of MXene and N-doped carbon significantly enhances the electronic conductivity of electrode, while the construction of hollow spherical structures effectively alleviates the instability of NiCo 2 S 4 /NC during the charge–discharge cycles, leading to the excellent charge storage performance with a high specific capacitance (1786 F g−1 at 1 A g–1) and impressive cycling stability (over 100 % capacitance retention after 10,000 cycles). A corresponding hybrid supercapacitor displays a high specific capacitance (190 F g−1 at 1 A g–1) with a maximum energy density (67 Wh kg−1 at 796 W kg−1) and great cycling stability (over 80 % capacitance retention after 10,000 cycles). The charge storage mechanism of NiCo 2 S 4 /MXene/NC is elucidated, revealing a combination of pseudocapacitive and battery-like behavior. Density functional theory (DFT) calculations indicate that the participation of MXene significantly increases the state density of NiCo 2 S 4 /MXene near the Fermi level compared to NiCo 2 S 4 , affirming its superior metallic conductivity. This work provides a facile route only with room-temperature stirring and high-temperature calcination to prepare well-defined metal sulfide composite microstructures with high electrochemical performance. [ABSTRACT FROM AUTHOR]

Flexible energy storage is the bottleneck for a variety of advanced electronic devices, and transition metal sulfides are regarded as an ideal candidate for this application due to their high capacitance, versatile microstructures, and low cost. However, to render this family of materials with high mechanical flexibility while maintaining their favorable electrochemical properties is especially challenging. Herein, we report a CNT@NiCo 2 S 4 hybrid film, in which bunches of ultrathin NiCo 2 S 4 nanosheet are firmly and uniformly anchored on a 3D CNT network. This material possesses tunable microstructures, high mechanical flexibility, good conductivity as well as lightweight, making it readily deployable in a flexible supercapacitor. Significantly, the asymmetric flexible supercapacitor based on this material possesses a high voltage output (1.8 V), a high energy/power density (59.5/34.5 Wh kg−1 at 900/18000 W kg−1), outstanding cycling stability (80.64% capacity retention after 10000 cycles), and excellent mechanical flexibility to withstand various deformations, all without sacrificing its performance. Moreover, this strategy has the potential to be extended to other metal sulfides or other carbon-substrates, which opens new avenues for the facile design and manipulation of flexible functional materials for future energy storage. Flexible, free-standing and ultralight NiCo 2 S 4 nanosheets/CNTs (NCS/CNT) films are prepared by a two-step solvothermal process. Uniform and ultrathin NiCo 2 S 4 nanosheets are intimately anchored on 3D CNTs network, retaining a rich porous structure. The as-prepared NCS/CNT hybrid film can be directly used as an electrode and delivers extraordinary electrochemical performance for flexible asymmetric supercapacitor. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, dicobalt tetrasulfide (NiCo 2 S 4) nanoneedles were successfully synthesized by a two-step hydrothermal method on nickel foam. A layer of polypyrrole (PPy) was further wrapped on the surface of the NiCo 2 S 4 nanoneedles by in-situ polymerization. The obtained NiCo 2 S 4 @PPy composite was investigated for supercapacitor applications, which exhibited a capacitance of 1842.8 F g−1 at 1 A g−1. An asymmetric supercapacitor device fabricated with an activated carbon negative electrode and NiCo 2 S 4 @PPy positive electrodes exhibited an energy density of 41.2 Wh kg−1 at 402.2 W kg−1 with a high charge–discharge cycling stability (92.8% after 5000 cycles). These results demonstrate that NiCo 2 S 4 @PPy electrodes have broad application prospects as energy storage electrode materials. [ABSTRACT FROM AUTHOR]

Supercapacitors (SCs) are drawing considerable attention because of their remarkable power density, long cycling stability, quick charging/discharging, and environmentally friendly characteristics. They are currently applied in electronic devices and wearable energy storage systems. Recently, the use of asymmetric supercapacitors (ASCs) has been acknowledged as a valid strategy to improve energy density of SCs due to the combination of electric double-layered anodes and redox-schemed cathodes. Here, mesoporous hollow NiCo2S4 sub-microspheres and porous graphene/single-walled carbon nanotubes are synthesized by a simple and elegant method without any use of templates. The as-synthesized products exhibit improved capacitive performance and extraordinary stability. An assembled asymmetric supercapacitor with graphene/single-walled carbon nanotubes and NiCo2S4 as its negative and positive electrodes, respectively, delivers a maximum energy density of 45.3 W h kg−1 (at 800 W kg−1) and an outstanding cycling life (87.5% over 20,000 cycles). This suggests that the obtained products possess huge potential to become the next generation of electrode materials for future energy storage devices. [ABSTRACT FROM AUTHOR]

As new and alternative energy storage devices to batteries and traditional capacitors, supercapacitors exhibit both high power and high energy density as well as good cycle life. NiCo2S4, a spinel‐structured transition metal sulfide with a high specific capacity, is considered to be a promising electrode material for supercapacitors with great application potential. However, the poor electrical conductivity of NiCo2S4 results in poor rate and cycle performance of the material, which limits its practical application. In this work, we design a composite by loading NiCo2S4 on the surface of carbon nanotubes (CNTs) to enhance the conductivity. The best‐performing CNTs@NiCo2S4 electrode materials were obtained after the optimized heat‐treatment of CNTs@SiO2 precursors. At a current density of 1 A g−1, the CNTs@NiCo2S4 composite exhibits a specific capacity of 216.4 mAh g−1 and a capacity retention of 75 % after 2000 cycles. Even at a high current density of 5 A g−1, the capacity can still retain 87 % of that under 1 A g−1. It is demonstrated that the electrochemical performance of NiCo2S4 can be effectively boosted by combining with conductive CNTs. [ABSTRACT FROM AUTHOR]

To design and prepare novel composites with strong electrode structure and superior electrochemical performances via a facile and convenient synthesis method is a significant challenge to develop the high-performance materials for energy storage and conversion devices. Herein, we fabricated a novel hybridization of two dimensional (2D) Ti 3 C 2 -MXenes nanosheets and one dimensional (1D) nickel-cobalt sulfide (NiCo 2 S 4) hollow nanotubes though the favorable electrostatic interaction between the negatively charged Ti 3 C 2 and positively charged NiCo 2 S 4 nanotubes. The electrode combined the good metallic conductivity of Ti 3 C 2 -MXenes and high pseudo-capacitance of NiCo 2 S 4 demonstrated the outstanding electrochemical performance for supercapacitors. Herein, 2D Ti 3 C 2 -MXenes/1D NiCo 2 S 4 hybrid electrode achieved an excellent specific capacitance of 1927 F g-1 at 2 mV s-1, long cycling stability for 4000 cycles and charming rate performances, which is mainly ascribed to the synergistic effect and interfacial interaction between two components. Particularly, the novel hybrid material with 1D and 2D hierarchical structures can provide additional electrochemical reaction sites, supply shorter paths for ions diffusion and electron transport, and effectively raise the charge transfer kinetics during the electrochemical process, which explores a new strategy aimed to develop 2D Ti 3 C 2 -MXenes energy storage devices with high electrochemical performance, and is possible potential for expansion into other application fields. Image 1 [ABSTRACT FROM AUTHOR]

NiCo 2 S 4 polyhedral architectures with high surface area, stable architecture and good crystallinity successfully are prepared with NiCo 2 O 4 as precursors. Impressive electrochemical performances including high specific capacitance, good rate capability and cycling stability are achieved owing to the particular polyhedral structure with more active sites for ions reaction and sufficient space for ions transmission. The as-prepared NiCo 2 S 4 electrode for supercapacitor displays high specific capacitance of 1298 F g−1 at 1 A g−1 and a superior rate capability of ~80.4% at 20 A g−1. Also, capacitance retention of 90.44% can be realized after 8000 cycles. In addition, the NiCo 2 S 4 as anode delivers high initial charge/discharge capacities of 807.6 and 972.8 mAh g−1 at 0.5 C. Dual-functional NiCo 2 S 4 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 NiCo 2 S 4 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 NiCo 2 S 4 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. [ABSTRACT FROM AUTHOR]

In recent years, spinel-type NiCo2S4 has been intensively studied as a supercapacitive material as it has a high theoretical capacitance, and is inexpensive and easy to synthesize. However, NiCo2S4 alone as an electrode material suffers from the drawback of an unsatisfactory cycling stability. In order to achieve better electrochemical performances, NiCo2S4-based composite materials have been developed for supercapacitors. In this Review, some recent research progress on NiCo2S4-based composite materials for supercapacitors is outlined. Furthermore, some suggestions for the further improvement of NiCo2S4-based materials for hybrid supercapacitors and the development of large-scale synthesis methods are proposed. [ABSTRACT FROM AUTHOR]

Although the synthesis of NiCo 2 S 4 (NCS)/g-C 3 N 4 (GCN)/PANI as an electroactive material has been extensively documented, assembling a Nickel cobalt sulfide (NCS) electrode with outstanding electrochemical efficiency at high current density is still difficult. In this work, the fabrication of a supercapacitor (Sc) electrode of petal-like NiCo 2 S 4 /g-C 3 N 4 /PANI using a hydrothermal, thermal condensation, and chemical oxidative polymerization method was done. In this nanocomposite, g-C 3 N 4 stabilized the metal atoms and PANI integration considerably improves ion mobility, leading to rapid charge transmission. Due to improvement in electron mobility, the eventual NiCo 2 S 4 /g-C 3 N 4 (0.40wt%) /PANI(A-3) electrode had shown a specific capacitance (C s) of 3.4 F/cm2 (1799.07 F/g) with 90% retention and 2700 cycles at the current density of 2 mA/cm2. A good rate capacity of 87.36% at 5 mA/cm2, 82.92% at 10 mA/cm2, and a 50.35% decline of its original capacitance at a high charge/discharge current density of 20 mA/cm2. This work demonstrates that the produced NiCo 2 S 4 /g-C 3 N 4 /PANI electrode has a high potential for use in energy storage gadget technologies. • Achieving exceptional electrochemical efficiency at high current densities. • Petal-like NiCo 2 S4/g-C 3 N 4 /PANI-based electrode has high structure stability and shows specific capacitance (C s) of 3.4 F/cm2 (1799.07 F/g) at a current density of 2 mA/cm2. • NiCo 2 S4/g-C 3 N 4 /PANI-based electrode has potential application in energy storage devices. [ABSTRACT FROM AUTHOR]

Battery-supercapacitor hybrid device (BSH) consisted of a battery-type electrode and a capacitor-type electrode is a promising candidate for both high energy and power density energy storage systems. In an effort to design a high-performance battery-type electrode of BSH, we propose a facile and artful two-step strategy to obtain NiCo 2 S 4 ultrathin nanosheets by utilizing bimetallic Co/Ni-ZIFs as a precursor. NiCo 2 S 4 nanosheets are directly grown on nickel foam via this method, which involves the growth of Co/Ni-ZIFs and the morphology of Co-Ni-S/NF transforms into ultrathin nanosheets through a simple sulfuration procedure. The as-prepared Co1Ni1-S/NF electrode achieves a high specific capacity of 301.1 mAh g−1 at 2 A g−1, which benefits from the synergistic interplay between Co and Ni ions and the unique 3D nanoarchitectures constructed by 2D ultrathin nanosheets. Moreover, Co1Ni1-S/NF and activated carbon/NF are chosen for fabricating a battery-supercapacitor hybrid device. The assembled Co1Ni1-S/NF//AC/NF BSH exhibits a large energy density of 48.65 W h kg−1 at a power density of 8.51 kW kg−1, a specific capacity of 80.56 mAh g−1 at 1 A g−1 and a remarkable stability over 5000 cycles at 5 A g−1. The encouraging results could provide new insights for energy storage systems. Unlabelled Image • Co-Ni-S was prepared by Co/Ni-ZIFs as a precursor for the first time. • NiCo 2 S 4 ultrathin nanosheets were obtained via a simple sulfuration procedure. • Co1Ni1-S/NF exhibits a high specific capacity and a remarkable capacity retention. • The assembled device shows high energy density and great stability over 5000 cycles. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Heterogeneous NiCo 2 S 4 @PPy core-sheath nanowire arrays on Ni foam is prepared. • A BAS was fabricated using NiCo 2 S 4 @PPy//AC-Ni foam as the electrode. • The particular BAS exhibits high capacitance of 7.36 F cm−2 (1925 F g−1). • The BAS maintains stable performance at 30–90 angles bending states. Abstract Bendable asymmetric supercapacitor (BAS) has been considered to be excellent energy storage for the flexible device and the electrode materials involved in BAS may bring in high electrochemical performance are crucial for practical application. In this work, a novel heterogeneous NiCo 2 S 4 @polypyrrole core-sheath nanowire is directly grown on Ni foam (NiCo 2 S 4 @PPy-Ni foam) by hydrothermal and electrochemical methods. The unique electrode shows a remarkable areal special capacitance of 6.3 F cm−2 at 50 mA cm−2 and exceptional capacitance retention of 91.2% after 5000 cycles. Using NiCo 2 S 4 @PPy-Ni foam and AC-Ni foam (active carbon-Ni foam) as positive and negative electrodes, respectively, a BAS (NiCo 2 S 4 @PPy//AC-Ni foam) was fabricated. The resulting exhibits a wide potential window of 1.8 V and a high capacitance of 7.36 F cm−2 (1925 F g−1). As a result, the BAS shows a maximum energy of 86.6 Wh kg−1 at a power density of 1046 W kg−1 and a perfect stability after 8000 cycles at a current density of 1.0 A cm−2. Furthermore, the BAS shows good flexibility and can withstand bending at 30–90 angles while keeping electrochemical performance constant. Such a BAS totally based on unique active materials and bendable Ni foam substrate which would be a promising candidate for using in wearable devices. [ABSTRACT FROM AUTHOR]

Bimetallic sulfide NiCo 2 S 4 is a highly promising electrode material for applications in novel sustainable high-performance energy storage devices, but its poor rate capability and cycling life need to be enhanced. Herein, we report a novel self-supporting hierarchical porous NiCo 2 S 4 /RGO/CNTs nanohybrids (NCSRCs) by co-modification of NiCo 2 S 4 nanoparticles with RGO and CNTs. The synergistic effect of RGO and CNTs not only constructs a hierarchical porous conductive network that facilitates charge transport kinetic and ion diffusion kinetic, but also provides abundant induced sites for the dispersion anchoring of NiCo 2 S 4 nanoparticles due to their high specific surface area with rich functional groups, which reduces the stacking of NiCo 2 S 4 nanoparticles and provides abundant exposed electroactive redox sites. Therefore, the electrochemical performance test results demonstrate that the NCSRCs electrodes exhibit significantly enhanced charge storage performance, showing a high specific capacity of 257.1 mAh g−1 at 0.3 A g−1 and good rate capability. In addition, the optimal NCSRC-24//N-RGO aqueous hybrid supercapacitor delivered a high specific energy of 33.67 Wh kg−1 and ultra-long durability with 82.44% capacity retention after 22,000 cycles. These results provide a facile approach to design and synthesize novel NCSRCs nanohybrids with superior properties for high-safety, sustainable and efficient aqueous energy storage devices. [Display omitted] • The novel NCSRCs nanohybrids are rationally designed and synthesized. • The rich groups in RGO/GO induced dispersed growth and refinement of NiCo 2 S 4. • The hierarchical porous NCSRCs exhibit rich exposed electroactive redox sites. • The NCSRCs electrodes have enhanced specific capacity and rate capability. • The assembled HSC delivers excellent energy density and ultra-long durability. [ABSTRACT FROM AUTHOR]

Abstract In this work, we report the synthesis of NiCo 2 S 4 nanosheets network and its application as electrode material for hybrid supercapacitors. The synthesis involves two-steps. Firstly, a precursor nanowires array is synthesized by a hydrothermal process. Then, the reaction between precursor and sodium sulfide through a vapor-phase diffusion process under hydrothermal condition leads to NiCo 2 S 4 nanosheets network. The unique network structure can prevent NiCo 2 S 4 nanosheets from aggregation and overlap. When act as an electrode material for supercapacitors, the NiCo 2 S 4 nanosheets network exhibits specific capacitances of 1956 F g−1 at 1 A g−1 and 1622 F g−1 at 20 A g−1. Cycling test shows 91.6% capacitance retention after 5000 charge–discharge cycles. The specific capacitance and rate capability of the NiCo 2 S 4 nanosheets network are higher than that of the NiCo 2 S 4 nanotubes array which was obtained from the direct reaction of precursor and sodium sulfide in solution. In addition, a hybrid supercapacitor device is assembled by using the NiCo 2 S 4 nanosheets network as positive electrode and porous carbon as negative electrode. The device exhibits an energy density of 27.5 W h kg−1 at a power density of 0.747 kW kg−1, and a power density of 6.03 kW kg−1 at an energy density of 18.75 W h kg−1. The results indicate that the NiCo 2 S 4 nanosheets network is an excellent electrode material candidate for high-performance supercapacitors. Highlights • NiCo 2 S 4 with a unique nanosheets network structure is prepared. • A vapor-phase diffusion process is involved during the synthesis process. • The NiCo 2 S 4 nanosheets network can be used as supercapacitor electrode material. • The NiCo 2 S 4 nanosheets network exhibit excellent capacitive activities. [ABSTRACT FROM AUTHOR]

High-capacitance electrode materials are extremely useful in high-performance supercapacitors. Here, an N and O codoped mesoporous carbon (MPC) material is reported. The MPC-3 exhibited a substantial capacitance of 306.6 F g−1 at 1 A g−1. NiCo 2 S 4 grown in situ on the MPC-3 formed the composite material (NCS/MPC). This composite material, 0.4-NCS/MPC-3, showed a specific capacitance of 551.8C g−1 at 1 A g−1; cyclic capacity was exceptional 95.9%, after 10,000 cycles. A 0.4-NCS/MPC-3//MPC-3 HSC device exhibited an energy density of 57.6 Wh kg−1 at a power density of 750 W kg−1. The device displayed a stable capacity of 90.2% after 10,000 cycles. This process is inexpensive and simple, highlighting value in the field of energy storage. [Display omitted] • The overall synthesis process of N and O codoped mesoporous carbon (MPC) is simple, environmentally benign, and economic. • NiCo 2 S 4 /MPC composite material (NCS/MPC) was obtained with NiCo 2 S 4 grown in situ on MPC. • The MPC-3 and 0.4-NCS/MPC-3 electrodes displays high capacitance and stability. • The HSC device has high energy density and power density. [ABSTRACT FROM AUTHOR]

In recent years, transition metal sulfides have been regarded as a promising energy storage material for supercapacitors, due to their high theoretical specific capacity and conductivity compared with other similar metal oxides and hydroxides. However, the sluggish diffusion dynamics and low capacitance impede its practical implement application. Herein, an advanced 3D nanocomposite of NiCo 2 S 4 /CuCo 2 S 4 heterostructure was designed via a time-saving, safe and efficient approach. The mass transfer kinetics of NiCo 2 S 4 /CuCo 2 S 4 nanocomposite has been significantly promoted owing to this novel heterostructure. Therefore, the NiCo 2 S 4 /CuCo 2 S 4 electrode materials reveal a superior specific capacitance (180.8 mAh g−1 at 2 A g−1) and excellent rate properties (84.7% capacitance retention from 2 to 20 A g−1). The asymmetric supercapacitor device assembled with NiCo 2 S 4 /CuCo 2 S 4 and activated carbon has an energy density of 37.0 Wh kg−1 at 400 W kg−1 and outstanding cyclic stability (93.3% remained after 10,000 cycles at 10 A g−1). Density functional theory (DFT) calculation further proves the electronic structure and the charge transfer can be tuned by the heterostructure of NiCo 2 S 4 and CuCo 2 S 4. This work offers a new perspective to design a high-performance electrode material in the field of supercapacitors. [Display omitted] • A 3D NiCo 2 S 4 /CuCo 2 S 4 nanoparticles composite was synthesized by a time-saving chemical deposition method. • NiCo 2 S 4 /CuCo 2 S 4 composite has a larger specific surface area than NiCo 2 S 4 or CuCo 2 S 4. • The heterostructure of NiCo 2 S 4 /CuCo 2 S 4 improves charge transport capacity. • The materials reveal a capacitance (180.8 mAh g−1 at 2 A g−1), rate properties (84.7% retention from 2 to 20 A g−1). [ABSTRACT FROM AUTHOR]

[Display omitted] • A porous carbon self-repairing g-C 3 N 4 /rGO@NiCo 2 S 4 nanocomposite was synthesized. • Substitutional-carbon crosslinking forms delocalized π-electrons by activating g-C 3 N 4. • The acid treatment fractured g-C 3 N 4 polymeric structures, increasing conductivity. • The pCRNCS electrode exhibited high specific capacitance (1938 F/g at 2 A/g). • The pCRNCS//AC ASC exhibited energy density of 66Wh/kg at a power density of 751 W/kg. In this work, porous carbon self-repairing g-C 3 N 4 (pCCN) nanosheets were synthesised using a solvothermal technique followed by calcination and acid treatment. A facile hydrothermal process is employed for the confined growth of NiCo 2 S 4 on porous carbon self-repairing g-C 3 N 4 /rGO heterostructure (pCRNCS) as hybrid material for supercapacitor electrodes. The improved electronic conductivity and activity of carbon self-repairing g-C 3 N 4 (CCN) than g-C 3 N 4 owing to the creation of extended delocalized π-electrons by the substitutional or interstitial C atoms in the structure and because of acid treatment, the larger planes of CCN are broken down into smaller segments, increasing the edge nitrogen and oxygen functional groups. The introduction of porous CCN led to the strong electrostatic interaction with GO and CCN which aided in the suppression of agglomeration of graphene sheets. The as-synthesised pCRNCS electrode showed remarkably high specific capacitance (1938 F/g at current density of 2 A/g). The excellent electrochemical activity is due to the 2D/2D heterostructure assembly of high surface area rGO and extended highly reactive region and defects in pCCN which facilitated the nucleation and confined growth of NiCo 2 S 4 in the framework. The constructed pCRNCS//AC ASC exhibited remarkable electrochemical properties, including a specific capacitance of 211 F/g at 1 A/g, an exceptional capacitance retention of 93.6% after 6000 cycles, and the maximum energy density of 66 Wh/kg at a power density of 751 W/kg. The excellent capacitive behaviour of porous carbon self-repairing g-C 3 N 4 /rGO@NiCo 2 S 4 assure the development of high-performance energy storage device. [ABSTRACT FROM AUTHOR]

• NiCo 2 S 4 /nickel foam electrode is fabricated by cyclic voltammetric deposition. • It achieves a specific capacitance of 2244.8 F/g at current density of 1 A/g. • It has a Coulombic efficiency of 99% after 1000 cycles of charge/discharge. The NiCo 2 S 4 /nickel foam composite electrodes have been fabricated by cyclic voltammetric deposition of NiCo 2 S 4 arrays on nickel foam, and the supercapacitor performance of the composite electrodes has been investigated. The results show that the electrode with 5 deposition cycles has the highest supercapacitor performance. It achieves a specific capacitance of 2244.8 F/g at current density of 1 A/g; it still has a capacitance retention rate of 66 % and a Coulombic efficiency of 99 % after 1000 cycles of charge/discharge. [ABSTRACT FROM AUTHOR]

• Hollow micro-sized spheres formed from NiCo 2 S 4 and CuCo 2 S 4 were successfully synthesized through facile solvothermal method. • Polypyrrole improved electrochemical performance of both as-prepared NiCo 2 S 4 and CuCo 2 S 4 materials. • Prepared symmetric supercapacitors from NiCo 2 S 4 /Polypyrrole and CuCo 2 S 4 / Polypyrrole were able to light up a 3.2 V white LED for 14.2 min and 10.1 min, respectively. NiCo 2 S 4 and CuCo 2 S 4 have been proven to be effective electrode materials in energy storage applications. In this study we investigate the influence of polypyrrole on the electrochemical behavior of these two potential materials. At first, high surface area micro-sized hollow spheres of NiCo 2 S 4 and CuCo 2 S 4 were successfully synthesized through facile solvothermal method and then pyrrole was polymerized through oxidative polymerization on the surface of as-prepared spheres. Resuls demonstrate improved electrochemical performance of both NiCo 2 S 4 and CuCo 2 S 4 after composing with polypyrrole. At current density of 1 A g–1, the specific capacitance of NiCo 2 S 4 /Polypyrrole and CuCo 2 S 4 /Polypyrrole was calculated to be 1412 F g–1 and 1005 F g–1, respectively. A symmetric supercapacitor assembled by NiCo 2 S 4 /Polypyrrole as both cathode and anode was able to light up a 3.2 V white LED for 14.2 min and an assembled supercapacitor from CuCo 2 S 4 /Polypyrrole as both cathode and anode lit up the same LED for 10.1 min. [ABSTRACT FROM AUTHOR]

• Control of microscopic morphology by modulation of the water-to-alcohol ratio. • The high capacitance of NCS-3 (857C/g) and the capacitance retention rate is 80% (20 A g−1). • Asymmetric supercapacitor shows high energy density 48.7 Wh kg−1 at a power density of 801 W kg−1. Because of high electrical conductivity, theoretical capacity, and numerous redox pairs, NiCo 2 S 4 has sparked a lot of interest in energy storage. In the paper, with citric acid as inductive agent, NiCo 2 S 4 mesoporous microspheres have been successfully prepared via solvothermal approach by regulating the solvent ratio (water/ethanol ratio = 1/3). It reveals that citric acid dominate in the nucleation and orientated growth of NiCo 2 S 4 and the morphology of NiCo 2 S 4 with different submicron structures can be tuned by the ratio of water/ethanol. The morphology, structure, and electrochemical properties of all NiCo 2 S 4 samples have been investigated. Among these samples, NiCo 2 S 4 mesoporous microspheres display the best electrochemical properties due to their unique mesoporous structure and high specific area. It has a high discharge capacity of 857C/g at a current density of 1 A/g, and exhibit exceptional rate capability (80 % retention even at 20 A/g). Additionally, when employed as positive of an asymmetric NiCo 2 S 4 //active carbon (AC) supercapacitor, it yields an energy density of 48.7 Wh kg−1 at 801 W kg−1 and 81 % capacity retention after 10,000 cycles at a current density of 5 A/g. The work describes a quick and easy way to increase the performance of NiCo 2 S 4 electrode materials and demonstrates its potential in practical application. [ABSTRACT FROM AUTHOR]

• Porous NiCo 2 S 4 nanosheets were easily synthesized using low-cost [CH 3 NH 3 ][M(HCOO) 3 ] compound. • Solvents affect the structure of the precursor [CH 3 NH 3 ][M(HCOO) 3 ] at room temperature. • Microflower-NiCo 2 S 4 //PC exhibits superior capacitance performance and excellent stability. Cost-effective and high-performance electrode materials for energy storage and conversion are essential for commercial applications. In this work, the influence of solvent on the morphologies of [CH 3 NH 3 ][M(HCOO) 3 ] precursors was studied to design and synthesize two-dimensional (2D) porous NiCo 2 S 4 nanosheets with different structures. As an electrode material for supercapacitors, Microflower-NiCo 2 S 4 exhibits excellent capacitance (1,141 F g−1 at 1 A g−1) and stability (88.2% of initial capacitance maintained after 5,000 cycles at 5 A g−1). Moreover, an asymmetric capacitor was constructed using Microflower-NiCo 2 S 4 and porous carbon (PC) and demonstrated an energy density of 51.25 Wh kg−1 at a power density of 397.5 W kg−1. When two Microflower-NiCo 2 S 4 //PC asymmetric supercapacitors were assembled in series, the device supplied power for an alarm clock with dimensions of 6.1 × 6.1 cm2 for more than 32 min. Therefore, the preparation of metal sulfides and metal oxides with hollow structures using a [CH 3 NH 3 ][M(HCOO) 3 ]-template has potential applications in energy storage and conversion. [ABSTRACT FROM AUTHOR]

Spinel nickel-cobalt sulfide (NiCo 2 S 4) supported on reduced graphene oxide (rGO) was fabricated through a facile one-step hydrothermal method for energy storage applications. The distribution of the NiCo 2 S 4 nanoparticles on the rGO surface was found to improve the supercapacitive performance of the assembled device. The NiCo 2 S 4 /rGO nanocomposite exhibits outstanding electrochemical behavior with a capacity (C)/specific capacitance (C s) of 536 C g−1/1072 F g−1 at a current density of 1 A g−1. To further investigate the electrochemical behavior of the NiCo 2 S 4 /rGO nanocomposite, a hybrid supercapacitor (HSC) was constructed utilizing a NiCo 2 S 4 /rGO positive electrode and an activated carbon (AC) negative electrode. The assembled NiCo 2 S 4 /rGO//AC HSC results in outstanding specific energy (E s) of 41.52 Wh kg−1 at a specific power (P s) of 1067 W kg−1 relative to previously reported NiCo 2 S 4 -based supercapacitors (SCs). The HSC had an E s of 36.51 Wh kg−1 at a P s of 2065 W kg−1. Additionally, excellent cycling stability of 82% capacitance retention after 3000 repeated charge/discharge cycles was accomplished. These realized results confirm that the NiCo 2 S 4 /rGO nanocomposite is a suitable electrode material for SCs. [Display omitted] • NiCo 2 S 4 /rGO nanocomposite was prepared using a one-step hydrothermal method as an electrode for a hybrid supercapacitor. • NiCo 2 S 4 nanoparticles are homogeneously distributed and tightly anchored to the surface of the wrinkled rGO. • NiCo 2 S 4 /rGO nanocomposite exhibited a specific capacitance of 1072 F g−1 at a current density of 1 A g−1. • NiCo 2 S 4 /rGO//AC hybrid supercapacitor showed specific energy of 41.52 W h kg−1 at a specific power of 1067 W kg−1. [ABSTRACT FROM AUTHOR]

[Display omitted] One-dimensional (1D) electrospun carbon nanofibers functionalized with NiCo 2 S 4 nanoparticles have been synthesized and exhibits excellent performance as a low-cost, lightweight, flexible and binder-free cathode for aqueous Ni-Zn batteries. • Electrospun carbon nanofibers functionalized with NiCo 2 S 4 nanoparticles are synthesized. • The CNF@NiCo 2 S 4 electrode is lightweight, flexible and binder-free. • The CNF@NiCo 2 S 4 exhibits excellent performance for aqueous Ni-Zn batteries. • The quasi-solid-state CNF@NiCo 2 S 4 //Zn battery is also fabricated with polymer electrolyte. Aqueous nickel-zinc (Ni-Zn) batteries hold great promise for large-scale energy storage systems. However, traditional Ni-based cathode electrodes are generally consist of none capacity contribution additives and heavy current collectors, resulting in a low percentage of the active materials. In this regard, developing lightweight, flexible and binder-free cathode electrodes for aqueous Ni-Zn batteries is highly desirable. Herein, for the first time, we develop a simple electrospinning technique to synthesize the one-dimensional (1D) electrospun carbon nanofibers functionalized with ternary NiCo 2 S 4 nanoparticles (denoted as CNF@NiCo 2 S 4) as a lightweight, flexible and binder-free electrode for aqueous Ni-Zn batteries. Based on the self-standing CNF@NiCo 2 S 4 film as cathode, the as-fabricated aqueous CNF@NiCo 2 S 4 //Zn battery exhibits a high capacity of 0.32 mAh cm−2 and 35.9 mAh cm−3 at a current density of 2 mA cm−2, and good rate performance (0.21 mAh cm−2 at 20 mA cm−2) and long-term cycling stability (83% capacity retention at 10 mA cm−2 after 2000 cycles). More importantly, a quasi-solid-state CNF@NiCo 2 S 4 //Zn battery is also fabricated, which also displays an impressive energy density of 362.3 Wh kg−1, indicating the potential towards practical applications. Impressively, the volumetric energy density of CNF@NiCo 2 S 4 //Zn battery are 58.2 mWh cm−3 (liquid) and 45.4 mWh cm−3 (quasi-solid-state), which are much larger than the values of other reported Ni-Zn batteries. Theses results indicate the self-standing CNF@NiCo 2 S 4 film is promising for for next generation electronic applications. [ABSTRACT FROM AUTHOR]

Herein, we report a comparison of the electrochemical performance of two kinds of NiCo2S4-based electrodes for solid-state hybrid supercapacitors (HSCs). For the binder-free electrode, NiCo2S4 was grown on Ni foam by the chemical bath deposition (CBD) method. For the binder-using electrode, NiCo2S4 powder was synthesized by the hydrothermal method. FESEM images depicted the hierarchical nanostructure of NiCo2S4 synthesized by the hydrothermal method and uniform distribution of nanostructured NiCo2S4 grown on Ni foam by the CBD method. Half-cell studies of both NiCo2S4 electrodes showed them exhibiting battery-type charge storage behavior. To assemble HSCs, NiCo2S4 and activated carbon were used as a positive and negative electrode, respectively. Electrochemical studies of the HSCs showed that the accessible potential window was wide, up to 2.6 V, through cyclic voltammetry (CV) analysis. Chronopotentiometry (CP) studies revealed that the energy and power densities of binder-using HSC were 51.24 Wh/kg and 13 kW/kg at 1 Ag−1, respectively, which were relatively higher than those of the binder-free HSC. The binder-free HSC showed 52% cyclic stability, relatively higher than that of the binder-using HSC. Both HSCs, with unique benefits and burdens on energy storage performance, are discussed in this work. [ABSTRACT FROM AUTHOR]

[Display omitted] • A well-designed Ti 3 C 2 T x /NiCo 2 S 4 @CC flexible electrode was fabricated. • Ultrathin MXene nanosheets are injected in electrode by spray coating technique. • The MXene material improved the conductivity of the electrode. Although MXenes with outstanding electrical conductivity possess great potential as energy-storage materials for flexible supercapacitors (SCs), the electrochemical performance of the pure MXene-based SCs are often restricted by inherent limitations such as inferior energy densities and serious aggregation. Alternatively, it will be an effective strategy to develop rationally designed composite electrodes that can simultaneously provide both high electrical conductivity and large surface area via complementary functions of each constituent. Here, hierarchically layered MXene nanosheets on nickel cobalt sulfide/carbon cloth (Ti 3 C 2 T x /NiCo 2 S 4 @CC, herein TNSC) was prepared through spray injection of MXene on nickel cobalt sulfide, which not only achieved an excellent specific capacitance at high current densities but also possess improved cycling stability. The optimized TNSC electrode shows maximum specific capacities of 2326F g−1 at a current density of 1 A g−1, and excellent cycling stability of 93.8% at 10 A g−1. We show that these outstanding electrochemical performances can be achieved by a proper loading amount of surface-coated Ti 3 C 2 T x , which can simultaneously enhance electrical conductivity and permeate ions to nickel cobalt sulfide. Furthermore, a quasi-solid‐state flexible SC (QFSC) based on TNSC presents a high energy density of 57.5 W h kg−1 at a power density of 800 W kg−1 in a wide potential window of 1.6 V. Therefore, the excellent electrochemical performances of the TNSC electrode makes it as a prominent candidate for high-performance and flexible energy storage devices. [ABSTRACT FROM AUTHOR]

The structural stability of electrode materials is the crux of significantly improve the electrochemical performance of pseudocapacitor electrodes. Herein, we demonstrate the preparation of NiCo 2 S 4 with core-shell and micro-porous structure on nickel foam as an efficient anode material for asymmetric supercapacitor (ASC) via hydrothermal and co-sulfurization processes. The NiCo 2 S 4 electrode shows a remarkable specific capacitance of 850.2 C g−1 at 1 A g−1, and retains 93.6 % original capacitance after 5000 cycles. Furthermore, the NiCo 2 S 4 electrode also have excellent electrochemical performance when used as an anode of asymmetric NiCo 2 S 4 //Active Carbon (AC) supercapacitor, which generates an energy density as 38.1Wh Kg−1 at 700 W kg−1 and 84.3% capacity retention after 5000 cycles. This work provide an efficiently method to suppress volume expansion during sulfuration reaction by core-shell structure, which potential application in transition metal sulfides electrode materials in electrochemical energy storage and conversion devices. [ABSTRACT FROM AUTHOR]

Bimetallic transition metal sulfides (TMSs) hold great promise as electrode materials for supercapacitive energy storage devices compared with their monometallic counterparts. However, it is still necessary to develop efficient synthetic protocols for favorable electrode architecture in order to further improve the electrochemical performance. This study presents a facile and controllable method to construct NiCo 2 S 4 heterostructure based on electrochemically exfoliated graphene with good adhesion, which involves the growth of bimetallic MOF precursor and in-situ conversion into NiCo 2 S 4 nanoparticles. This integrated architecture was found to be efficient for supercapacitive energy storage, as evident by the improved utilization of NiCo 2 S 4 and excellent electrochemical performance including high capacity of 1802.5 F g−1 at 1 A g−1 and good rate capability (86.1% capacity retention at 10 A g−1). Additionally, N-doped mesoporous carbon spheres (NMCS) were synthesized by sacrificial template method and used as anode for practical application. Benefiting from good charge balance and compatibility, the assembled EEG@NiCo 2 S 4 //NMCS hybrid supercapacitor (HSC) exhibited outstanding energy density (30.4 Wh kg−1 at 800.0 W kg−1) and excellent cycling stability (80.1% capacitance retention after 9000 cycles). • Advanced NiCo 2 S 4 /graphene heterostructure is created by conversion of MOF based on electrochemically exfoliated graphene. • The heterostructure is of importance to promote electrochemical performance compared with NiCo 2 S 4 and Ni 3 S 4 /NiS counterparts. • The N-doped mesoporous carbon anode with multidimensional transport pathways allows for efficient electrical/ionic transfer. [ABSTRACT FROM AUTHOR]

Incorporation of electroactive Fe 2 O 3 and NiCo 2 S 4 (NCS) into graphene aeorgel (GA) is presented in this work. The efficient adsorption of precursor ions on the graphene oxides sheets and subsequent hydrothermal gelation yield the GA-Fe 2 O 3 and GA-NCS composites that can be used as negative and positive electrode, respectively, for constructing a high-energy asymmetric supercapacitor (ASC). Influences of mass contents of Fe 2 O 3 and NCS on capacitive performances of GA-Fe 2 O 3 and GA-NCS electrodes are systematically investigated in KOH aqueous electrolyte. The uniform distribution of Fe 2 O 3 on the graphene sheets (GS) and the NCS nanoparticles wrapped by GS provide sufficient electroactive sites for Faradaic redox reactions, while the GA interconnected with macropores offers favorable channels for electrolyte transport. Thereby, the specific capacitance of 200 F g−1 (178 C g−1) and 386 F g−1 (170 C g−1) are achieved for GA-Fe 2 O 3 (20 wt% Fe 2 O 3) and GA-NCS (77 wt% NCS), respectively. A coin-type capacitor built with GA-Fe 2 O 3 as negative electrode and GA-NCS as positive electrode delivers a specific capacitance of 93 F g−1 (128 C g−1) at 0.1 A g−1, corresponding to a maximum energy density of 25 Wh kg−1 at a power density of 54 W kg−1. Meanwhile, the ASC also exhibits a good rate capability and a satisfying cycling stability with 72.3 % capacitance retention after cycling at 2 A g−1 for 5000 cycles. These results show great potentials of GA-Fe 2 O 3 and GA-NCS electrodes in electrochemical energy storage. [ABSTRACT FROM AUTHOR]

• Key strategies for improving electrochemical properties of NiCo 2 S 4 -based electrodes are proposed. • This work provides one specific perspective for the development of NiCo 2 S 4 -based composites used in energy storage devices. • This work is helpful to researchers around the world who are working on the synthesis and application of nanostructure TMSs. NiCo 2 S 4 has received wide attention as a promising electrode material for supercapacitors (SCs), Li-ion batteries (LIBs), and Na-ion batteries (SIBs) in the past few years because of its excellent mechanical property, low cost, and rich redox chemistry. In addition, NiCo 2 S 4 has higher electronic conductivity than the corresponding nickel cobaltite oxide (NiCo 2 O 4) and higher redox ability than the corresponding single-phase sulfide. Nevertheless, the actual applications of pristine NiCo 2 S 4 without unique morphology have been restrained on account of the small specific surface area, agglomeration, and big volume change during cycling, resulting in low reversible specific capacity (capacitance) and poor cycle stability at high rates. Constructing NiCo 2 S 4 with novel nanostructures and heterogeneous core-shell structures have been considered as one of the most promising strategy to solve these problems. In the present review, the recent research developments in the electrochemical reaction mechanisms, preparation methods, morphology control, and electrochemical property of NiCo 2 S 4 -based composites as electrode materials for SCs and secondary batteries are summarized. The main focus is to discuss the dominant factors affecting the electrochemical properties of NiCo 2 S 4 -based materials, and then highlight hopeful strategies to improve specific capacitances/capacities and cycling stability, especially at high current densities. Finally, several insights into the future developments, challenges, and prospects of NiCo 2 S 4 -based composites for SCs, LIBs, and SIBs are proposed. [ABSTRACT FROM AUTHOR]

Although potassium ion batteries (KIBs) have been invested in development as an emerging low-cost, high-content energy storage system at present. However, the large ionic radius of K+-ion lead to poor rate performance and low cycle life. Therefore, it is extremely necessary to develop a new type of potassium storage material. Here, we report a novel three-dimensional (3D) structural self-supported anode composite material for KIBs, which consists of tapered rod-shaped nanomaterial NiCo 2 S 4 and nitrogen-doped hollow carbon nanofibers (NiCo 2 S 4 @N-HCNFs). Then, the composite material was obtained by high temperature carbonization and hydrothermal reaction process. The prepared electrode materials were used to assemble K half-cells for electrochemical performance measurement, achieved the capacity of 263.7 mAh g−1 after 200 cycles at a current density of 100 mA g−1 and an outstanding stability of retaining 134.3 mAh g−1 at 3200 mA g−1 after 600 cycles. It has superior performance and convenient synthesis process over other reported metal sulfides self-supported anode materials for KIBs so far. The novel structure not only shorten the ion transmission distance, but also increase the contact area with the electrolyte. It can improve electrochemical performance effectively. Image 1 • 3D composite NiCo 2 S 4 @N-HCNFs self-supported anode was successfully fabricated. • The synthetic sample exhibits excellent potassium-storage performance. • The excellent performance thanks to the special structure of NiCo 2 S 4 @N-HCNFs. [ABSTRACT FROM AUTHOR]

Asymmetric supercapacitor as a promising energy storage system utilizes both redox-type and electric double-layer type electrodes in one single device, but it is urgent to design sustainable electrodes with low-cost and high-performance. Herein, hybrid NiCo 2 S 4 /carbon and porous carbon electrodes are prepared by using carboxylated cellulose nanofibers as the carbon source due to the carbon-rich backbone and abundant hydroxyl groups on the surface. The NiCo 2 S 4 /carbon electrode displays a large specific capacity/capacitance of 783C g−1/1569 F g−1 at 0.5 A g−1 with the capacity retention ratio of 78% after 5000 cycles. The specific capacitance of porous carbon material is 376 F g−1 at 1 A g−1. With the utilization of the different electrochemical potential windows, an asymmetric device is fabricated by using the NiCo 2 S 4 /carbon hybrid and porous carbon as the positive and negative electrodes, showing a high energy density of 53.7 W h kg−1 at 184.4 W kg−1. The asymmetric device maintains an excellent capacity retention rate of 97% after 10,000 cycles. These promising properties are related with the synergistic effect from the high-performance positive and negative electrodes. Considering the advantage in terms of sustainability, this work paves the way for the design of advanced electrodes for high-efficiency energy storage equipment. Image 1 • Carbon coated metal sulfide and porous carbon were obtained using cellulose nanofibers. • Asymmetric supercapacitor with high energy was fabricated. • This work opens a new avenue to design sustainable electrodes for energy storage. [ABSTRACT FROM AUTHOR]

The Core-branched NiCo 2 S 4 @CoNi-LDH heterostructure contributes to high-efficient charge storage. • The Core-branched NiCo 2 S 4 @CoNi-LDH heterostructure is facilely prepared. • The Core-branched NiCo 2 S 4 @CoNi-LDH heterostructure exhibited excellent conductivity and high-efficient charge storage. • The CN-LDH NSs@NCS NSs//AC device delivered an high energy density of 93.21 Wh kg−1 at 1.045 kW kg−1. Constructing hierarchical core-branched configuration from the well-known multicomponent metal hydroxides/sulfides is a way to further tune and utilize distinctive species. Herein, we develop a novel core-branched heterostructure based on NiCo 2 S 4 nanosheets (NCS NSs) branched on CoNi-LDH nanosheets (CN-LDH NSs), which involves facile hot-air oven-based and electro-deposition methods. The CN-LDH NSs acts as the host stem and supports NCS NSs electroactive species to provide reliable electrical contact for electron transfer; whereas the highly active NCS NSs "branch" on the outside of CN-LDH NSs "core" provide sufficient access to active sites, and electron transport regions for the valence transitions of Ni2+/Ni3+ and Co2+/Co3+/Co4+ during redox process. The CN-LDH@NCS NSs electrode achieves a notable specific capacity of 1385.7 C g−1 at 1 A g−1, and good rate capability. Additionally, the as-prepared CN-LDH@NCS NSs//AC device exhibits a high energy density of 93.21 Wh kg−1 at a power density of 1.045 kW kg−1 and satisfying cycling lifespan, with nearly 81.49% capacitance retention after 7000 cycles (20 A g−1). [ABSTRACT FROM AUTHOR]

• C/NiCo 2 S 4 hollow nanospheres are fabricated for supercapacitor electrode materials. • C/NiCo 2 S 4 electrode exhibits remarkable specific capacitance and cycle stability. • Hierarchically hollow architecture and compositional features give high performance. • An asymmetric supercapacitor was assembled with enhanced performance. Binary transition metal sulfides hold immense promise for use in energy storage devices thanks to their higher electronic conductivity and capacity compared to that of the mono-metal sulfides arising from the richer redox reactions. Herein, hierarchically hollow C/NiCo 2 S 4 nanosphere composites have been synthesized through carbon coating and hydrothermal processes with SiO 2 nanosphere and glucose as the hard template and carbon source, respectively. The interconnected NiCo 2 S 4 nanosheets, void spaces in the interior of nanospheres and the conductive carbon layer enable the C/NiCo 2 S 4 composite electrode to achieve an outstanding conductivity and good stability. Accordingly, the hollow C/NiCo 2 S 4 nanosphere electrode exhibits an extraordinary specific capacitance of 1545 F g−1, as well as an enhanced cycling stability (90.1% after 6000 cycles) at a high current density of 10 A g−1. Satisfactory energy density (34.1 Wh kg−1 at 160 W kg−1) and high power density (8000 W kg−1 at 19.8 Wh kg−1) can be obtained by fabricating an asymmetric supercapacitor with activated carbon in the operation window of 0–1.6 V. These encouraging results further reveal the promising prospects of the as-prepared C/NiCo 2 S 4 nanocomposite for high efficient electrochemical supercapacitor. [ABSTRACT FROM AUTHOR]

The rapid development of portable and wearable electronic devices requires novel energy storage devices. Flexible, high-performance electrode materials are critical for meeting the demands yet remain challenging. Here, a rationally designed flexible NiCo 2 S 4 @rGO/rGO film constructed with NiCo 2 S 4 @rGO frameworks is successfully prepared through a step-wise process (hydrothermal, freeze-drying, vacuum filtration, and then sulfurization/reduction). The NiCo 2 S 4 @rGO/rGO film as flexible electrode shows typical battery-type faradaic redox features and exhibits a high specific capacitance of 1100.0 F g−1 at 1 A g−1, a good rate performance of 89.1% capacity retention at 10 A g−1 coupled with long cycling stability of 90.2% after 5000 cycles. The good electrochemical performance is mainly attributed to the loose layered structure and strong interaction between NiCo 2 S 4 and rGO nanosheets, which enhance the diffusion of electrolyte ions/electrons and decreases intrinsic resistance and contact resistance. A flexible hybrid supercapacitor assembled using the NiCo 2 S 4 @rGO/rGO film as cathode and the rGO film as anode shows a high energy density of 30.0 Wh kg−1 at a power density of 857.6 W kg−1 at an extended operating voltage of 1.8 V. The method can also be readily adapted for loading other bimetallic sulfides on rGO films, indicative of its feasibility and flexibility to prepare rGO-based hybrid film for high-performance flexible electrochemical energy storage. • A flexible NiCo 2 S 4 @rGO/rGO film with a unique loosely-layered structure was constructed with NiCo 2 S 4 @rGO frameworks. • The NiCo 2 S 4 @rGO/rGO film exhibits excellent electrochemical performances. • A flexible hybrid supercapacitor delivers high energy and power density. • This work provides an ideal and feasible route of constructing flexible rGO-based hybrid film electrodes. [ABSTRACT FROM AUTHOR]