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Gel polymer‐based lithium batteries exhibit a unique combination of advantageous properties, including the favorable interfacial contact characteristic of liquid‐state batteries and the inherent stability of solid‐state batteries. For Li–air batteries operated in the semi‐open atmosphere, implementing in situ synthesized gel polymer electrolytes (GPEs) is effective in mitigating the environment‐induced challenges. In this study, a dimethyl sulfoxide (DMSO)‐based GPE in situ initiated by the toluene‐2,4‐diisocyanate (TDI) and 1,4‐benzenediboronic acid (BDBA) is designed to enable the stable operation of lithium–air batteries. The integration of in situ polymerization and polyvinyl alcohol's functional group engineering not only brings benefits to the interfacial contact and electrochemical stability of the battery but also mitigates the moisture sensitivity and volatility of the DMSO electrolyte in the ambient environment. In addition, the GPE can promote the formation of a robust protection film on the lithium surface. As a result, the designed GPE makes the batteries fully leverage their outstanding cycling stability in the ambient environment (241 cycles at 500 mA g−1 and 1000 mAh g−1). Moreover, an optimized Li–air pouch cell structure incorporating the GPE achieves a boasted energy density of 757.5 Wh kg−1, providing a significant technical pathway to bring Li–O2 batteries to practical Li–air batteries. [ABSTRACT FROM AUTHOR]

Dielectric polymer-based composites have demonstrated enormous promise in the applications of electrostatic film capacitors due to their exceptional insulating characteristics. However, the achievement of great energy-storage density (U e) is always difficult in linear dielectric polymer-based composites for operation at weak field strength due to the low permittivity (ϵ r) and electric displacement difference (D max − D rem) values. Here, a tri-layered configuration of multicomponent polymeric films is proposed. The outer layers of the tri-layered composite are linear dielectric polymethyl methacrylate (PMMA), and the inner layer is a nonlinear polymer incorporating a low number of polydopamine-modified barium titanate particles (BT@PDA). An increased ϵ r of 8.9@1 kHz is achieved in the designed composite featuring only 2 wt% BT@PDA fillers, equivalent to 234% of the PMMA (∼3.8@1 kHz) matrix. An improved U e of 9.3 J cm−3 at 340 MV m−1 is endowed in the designed film, implying an enormous ∼343% increment of the energy storage compared to the benchmark biaxially oriented polypropylene (∼2.1 J cm−3 at 300 MV m−1). All these advantages present a practical strategy for supplying linear dielectric polymer-based composites with anticipative capacitive energy-storage properties for operation at weak field strengths. [ABSTRACT FROM AUTHOR]

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Sodium‐ion hybrid capacitors (SIHCs) are considered a prospective alternative to lithium‐ion batteries (LIBs) since there are rich and available sodium reserves. Here, nitrogen‐doped carbon tubes (N‐MJ) derived from metaplexis japonica fluff are prepared by using a facile method of etching and peeling the fluff with urea to prepare a Na+ storage anode. With prominent traits in terms of structure and a high nitrogen content (11.08 %), N‐MJ exhibits exceptional Na+ storage performance with a high reversible capacity (390.9 mAh g−1 at 50 mA g−1) and excellent long‐term circulation (208.1 mAh g−1 after 2650 cycles at 1 A g−1). Systemic kinetic analysis manifests that the extraordinary performance is responsible for the large‐scale capacitance control. Furthermore, the SIHCs assembled by using N‐MJ and activated carbon (AC) presents a maximum energy density of 111.4 Wh kg−1 (at 445.8 W kg−1) and power density of 2455.2 W kg−1 (at 34.1 Wh kg−1). Notably, the developed SIHCs maintain a 100 % capacity retention rate at 1 A g−1 after 5000 cycles. Overall, our work not only provides a good choice for storage Na+ anode materials, but also supplies a feasible method for the recycling of waste biomass. [ABSTRACT FROM AUTHOR]

Molybdenum trioxide (MoO3) has recently aroused intensive interest as a renowned conversion‐type anode of Li‐ion batteries (LIBs). Nevertheless, the inferior rate capability, sluggish reaction kinetics, and fast capacity decay during a long‐term charge/discharge process seriously inhibits large‐scale commercial application. Herein, abundant oxygen vacancies and MXene nanosheets are elaborately introduced into MoO3 nanobelts through hydrazine reduction and electrostatic assembly to accelerate the ionic and electronic diffusion/transport kinetics for LIBs. Benefitting from the accelerated ion diffusion kinetics, enhanced electrical conductivity, and additional active sites induced by oxygen vacancies as well as the robust interfacial contact, the prepared MoO3−x/MXene heterostructure exhibits excellent lithium‐ion storage performances. First‐principles calculations indicate that the adsorption of Li+ ion and the electrical conductivity are significantly enhanced for the MoO3−x/MXene heterostructure. Thus, the composite exhibits high reversible capacity of 1258 mAh g−1 at 0.1 A g−1 for Li‐ion storage and retains 474 mAh g−1 at 10 A g−1, remarkably higher than those of the previously reported MoO3‐based anode materials. More importantly, the composite is fabricated with commercial LiFePO4 into a full LIB, which displays an unparalleled energy density of 330 Wh kg−1. [ABSTRACT FROM AUTHOR]

2D MXene materials have attracted intensive attention in energy storage application. However, MXene usually undergoes serious face‐to‐face restacking and inferior stability, significantly preventing its further commercial application. Herein, to suppress the oxidation and self‐restacking of MXene, an efficient and fast self‐assembly route to prepare a 3D porous oxidation‐resistant MXene/graphene (PMG) composite with the assistance of an in situ sacrificial metallic zinc template is demonstrated. The self‐assembled 3D porous architecture can effectively prevent the oxidation of MXene layers with no evident variation in electrical conductivity in air at room temperature after two months, guaranteeing outstanding electrical conductivity and abundant electrochemical active sites accessible to electrolyte ions. Consequently, the PMG‐5 electrode possesses a striking specific capacitance of 393 F g−1, superb rate performance (32.7% at 10 V s−1), and outstanding cycling stability. Furthermore, the as‐assembled asymmetric supercapacitor possesses a pronounced energy density of 50.8 Wh kg−1 and remarkable cycling stability with a 4.3% deterioration of specific capacitance after 10 000 cycles. This work paves a new avenue to solve the two long‐standing significant challenges of MXene in the future. [ABSTRACT FROM AUTHOR]

Summary: Transition metal sulfides show excellent performance in an aqueous supercapacitor. However, all‐solid‐state supercapacitors are attracting more and more interest because of thinner, lighter, and more flexible. Binary sulfides Ni3Co6S8 nanowire arrays (NCS) are directly grown on a nitrogen‐doped carbon foam (NCF) through hydrothermal reaction, which is applied as a binder‐free electrode for all‐solid‐state supercapacitor. The unique needlelike structure assembled by nanosheet effectively increases the utilization efficiency of active materials and promotes electrochemical performance. The NCS‐NCF electrode shows promising application potential for wearable electronic devices due to the flexibility of NCF. A high‐specific capacitance of 243 mAh g−1is delivered by NCS‐NCF electrode, which also exhibits good rate behavior along with outstanding cycle stability. The NCS‐NCF electrode (positive electrode) and NCF electrode (negative electrode) are employed to assemble asymmetric all‐solid‐state supercapacitor. When the high power density is 675 W kg−1, the energy density of supercapacitor reaches the maximum of 28.31 Wh kg−1. The specific capacitance of supercapacitors could maintain 84%, after 10 000 cycles of galvanostatic charge and discharge under 4 A g−1, indicating the potential application of NCS‐NCF electrode as an excellent supercapacitor electrode material in flexible, wearable energy storage systems. [ABSTRACT FROM AUTHOR]

Potassium‐ion hybrid capacitors have attracted increasing attention due to good energy density, high power density, and low cost. Ti3C2Tx‐MXene is considered as a promising anode material for K ion storage. However, undesirable stacking issues decrease its exposed area and breeds sluggish K ion transport. Herein, a facile spray‐lyophilization strategy is proposed to construct stacking‐resistant Ti3C2Tx with 3D structures. As‐prepared Ti3C2Tx hollow spheres/tubes present stack resistance, a large specific surface area, and a short ion diffusion pathway. When serving as an anode material, it shows enhanced capacity and thickness‐independent rate performance compared to 2D Ti3C2Tx. After 10 000 cycles, a specific capacity of 122 mAh g−1 is obtained at 1 A g−1. Systematic kinetics analyses demonstrate the significance of concentration polarization on the electrode's rate ability. Furthermore, a 3D Ti3C2Tx‖hierarchical porous activated carbon (HPAC) K‐ion hybrid capacitor is assembled and displays remarkable energy and power densities with energy retention of 100% after 10 000 cycles at 1 A g−1. Following this strategy, other 3D structures from nanosheets can also be obtained, such as 3D Ti3C2Tx microtubes and graphene oxide nanoscrolls. This study provides a viable approach to solve the stacking issues of 2D nanosheets to promote the application of 2D materials. [ABSTRACT FROM AUTHOR]

Summary: Sodium‐ion hybrid capacitors are a prospective energy storage device candidate that couples the superiorities of battery‐type and capacitive storage mechanisms. In this study, we fabricate a composite of NiCo2O4 nanowires with carbon tubular bundles (CTBs) via a facile hydrothermal and annealing procedure. The density functional theory (DFT) calculations are performed to evaluate the bonding strength between the two components of the composite, the binding energy of the NiCo2O4 is calculated to be −0.952 J m−2, indicating that the NiCo2O4 nanowires can be stabilized on both sides of the carbon tubular bundles, which leads to a good cycling performance. Moreover, the composite in this work exhibits a metallic property because of the introduction of carbon material. As expected, when used for sodium storage, the NiCo2O4/CTBs shows a high capacity of 298 mA h g−1 at 1 A g−1 and high capacity retention of 92% after 500 cycles, which are superior than the bare NiCo2O4 electrode. Consequently, the sodium‐ion hybrid capacitor is also assembled with NiCo2O4/carbon tubular bundles and commercial activated carbon, which achieves high energy density of 99 Wh kg−1 in a wide potential range from 0.5 V to 4.0 V. [ABSTRACT FROM AUTHOR]

The flexible Li‐O2 battery is suitable to satisfy the requirements of a self‐powered energy system, thanks to environmental friendliness, low cost, and high theoretical energy density. Herein, a flexible porous bifunctional electrode with both electrocatalytic and photocatalytic activity was synthesized and introduced as a cathode to assemble a high‐performance Li‐O2 battery that achieved an overpotential of 0.19 V by charging with the aid of solar energy. As a proof‐of‐concept application, a flexible Li‐O2 battery was constructed and integrated with a solar cell via a scalable encapsulate method to fabricate a flexible self‐powered energy system with excellent flexibility and mechanical stability. Moreover, by exploring the evolution of the electrode morphology and discharge products (Li2O2), the charging process of the Li‐O2 battery powered by solar energy and solar cell was demonstrated. [ABSTRACT FROM AUTHOR]

Abstract Herein, we present the synthesis of oxygen vacancies-rich α -MoO 3- x nanobelts through a novel defect-engineering strategy. The oxygen-vacancies could not only greatly increase the interlayer spacing and the electrical conductivity of MoO 3 , but also significantly enhance the electrochemical activity, which promotes faster charge storage kinetics. Meanwhile, to further facilitate the electron transfer and ion transport, a graphene nanomesh-carbon nanotube/MoO 3- x (GC/MoO 3- x) nanocomposite with three-dimensional sandwiched structure was fabricated, which displays high specific capacity up to 306 C g−1 as well as high volumetric capacity of 692 C cm−3. Our fabricated asymmetric supercapacitor (ASC) with the GC/MoO 3- x and GC/MnO 2 nanocomposites as anode and cathode, respectively, exhibits an ultrahigh energy of 150 Wh kg−1, corresponding to an impressive volumetric energy density of 319 Wh L−1. Notably, both the gravimetric and volumetric energy densities are much higher than most of the previously reported metal oxide based ASCs in aqueous electrolytes. Furthermore, the ASC displays an ultra-long lifespan with 101% retention ratio after 30,000 cycles. The outstanding performances of GC/MoO 3- x composite render it a highly promising candidate for next-generation supercapacitors with both high energy and power densities in future applications, especially in greatly limited space. Graphical abstract fx1 Highlights • Oxygen vacancies-rich MoO 3- x is prepared through a novel defect-engineering strategy. • Oxygen-vacancies greatly increase the interlayer spacing, electrical conductivity and electrochemical activity of MoO 3. • High specific capacity up to 306 C g−1 (692 C cm−3) is obtained. • An ultrahigh volumetric energy density of 319 Wh L−1 is obtained, the highest value for aqueous supercapacitors up to date. • ASC displays an ultra-long lifespan with 101% retention ratio after 30,000 cycles. [ABSTRACT FROM AUTHOR]

NiMoO4 has attracted intensive attention as one of the promising ternary metal oxides because of its high specific capacitance and electrical conductivity compared to traditional transition-metal oxides. In this study, NiMoO4 nanorods uniformly decorated on graphene nanosheets (G-NiMoO4) are synthesized through a facile hydrothermal method. The prepared G-NiMoO4 composite exhibits a high specific capacitance of 714 C·g−1 at 1 A·g−1 and an excellent rate capability, with a retention ratio of 57.7% even at 100 A·g−1. An asymmetric supercapacitor (ASC) fabricated with the G-NiMoO4 composite as the positive electrode and Fe2O3 quantum dot-decorated graphene (G-Fe2O3-QDs) as the negative electrode delivers an ultrahigh energy density of 130 Wh·kg−1, which is comparable to those of previously reported aqueous NiMoO4-based ASCs. Even when the power density reaches 33.6 kW·kg−1, an energy density of 56 Wh·kg−1 can be maintained. The ASC device exhibits outstanding cycling stability, with a capacitance retention of 113% after 40,000 cycles. These results indicate that the G-NiMoO4 composite is a promising candidate for ASCs with ultrahigh energy density and excellent cycling stability. Moreover, the present work provides an exciting guideline for the future design of high-performance supercapacitors for industrial and consumer applications via the simultaneous use of various pseudocapacitive materials with suitable potential windows as the positive and negative electrodes. [ABSTRACT FROM AUTHOR]

A strategy to prepare flexible and conductive MXene/graphene (reduced graphene oxide, rGO) supercapacitor electrodes by using electrostatic self-assembly between positively charged rGO modified with poly(diallyldimethylammonium chloride) and negatively charged titanium carbide MXene nanosheets is presented. After electrostatic assembly, rGO nanosheets are inserted in-between MXene layers. As a result, the self-restacking of MXene nanosheets is effectively prevented, leading to a considerably increased interlayer spacing. Accelerated diffusion of electrolyte ions enables more electroactive sites to become accessible. The freestanding MXene/rGO-5 wt% electrode displays a volumetric capacitance of 1040 F cm-3 at a scan rate of 2 mV s-1, an impressive rate capability with 61% capacitance retention at 1 V s-1 and long cycle life. Moreover, the fabricated binder-free symmetric supercapacitor shows an ultrahigh volumetric energy density of 32.6 Wh L-1, which is among the highest values reported for carbon and MXene based materials in aqueous electrolytes. This work provides fundamental insight into the effect of interlayer spacing on the electrochemical performance of 2D hybrid materials and sheds light on the design of next-generation flexible, portable and highly integrated supercapacitors with high volumetric and rate performances. [ABSTRACT FROM AUTHOR]

Highlights: A freestanding MXene-derived defect-rich TiO2@reduced graphene oxides (M-TiO2@rGO) foam electrode was fabricated. M-TiO2@rGO presents fast Na+ storage kinetics due to capacitive contribution. M-TiO2@rGO foam electrode displays a capacity retention of 90.7% after 5000 cycles. Sodium ion batteries and capacitors have demonstrated their potential applications for next-generation low-cost energy storage devices. These devices's rate ability is determined by the fast sodium ion storage behavior in electrode materials. Herein, a defective TiO2@reduced graphene oxide (M-TiO2@rGO) self-supporting foam electrode is constructed via a facile MXene decomposition and graphene oxide self-assembling process. The employment of the MXene parent phase exhibits distinctive advantages, enabling defect engineering, nanoengineering, and fluorine-doped metal oxides. As a result, the M-TiO2@rGO electrode shows a pseudocapacitance-dominated hybrid sodium storage mechanism. The pseudocapacitance-dominated process leads to high capacity, remarkable rate ability, and superior cycling performance. Significantly, an M-TiO2@rGO//Na3V2(PO4)3 sodium full cell and an M-TiO2@rGO//HPAC sodium ion capacitor are fabricated to demonstrate the promising application of M-TiO2@rGO. The sodium ion battery presents a capacity of 177.1 mAh g−1 at 500 mA g−1 and capacity retention of 74% after 200 cycles. The sodium ion capacitor delivers a maximum energy density of 101.2 Wh kg−1 and a maximum power density of 10,103.7 W kg−1. At 1.0 A g−1, it displays an energy retention of 84.7% after 10,000 cycles. [ABSTRACT FROM AUTHOR]

A positive nematic liquid crystal (5CB) sample is confined in cylindrical cells under strong or weak axial anchoring boundary conditions when a radial nonuniform low-frequency electric field is applied and the flexoelectric effect is taken into account. Based on the Frank elastic free energy, the surface energy of the Rapini–Papoular approximation, the polarization free energy and the flexoelectric free energy caused by electric field, we obtain the free energy density of the nematic and solve the corresponding Euler–Lagrange equation numerically. We investigate the director distribution, the critical voltage and the critical exponent of nematic liquid crystal in cylindrical cells. It follows that the critical exponent is the classical one. It is also shown that the critical voltage in the system is affected by the flexoelectric effect, the geometric effect and radial weak anchoring effect on the cylindrical surfaces. A new type of director transition caused by the flexoelectric effect, the dielectric coupling effect and the radial weak anchoring effect is found. [ABSTRACT FROM AUTHOR]

The N, S dual-doped porous graphitic carbon materials with the high graphitization degree were synthesized from the light fraction of coal tar pitch and waste sponge through a facile "killing two birds with one stone" process. The suitable N and S doping not only can provide extra electroactive sites, but also can improve the storage capacity of Zn ions through the decrease in E a value for LC-750 cathode. [Display omitted] • The N, S dual-doped porous graphitic carbon is prepared via a "killing two birds with one stone" strategy. • The LC-750 exhibits superior pore structures and high graphitization degree. • The LC-750 cathode shows high capacity and excellent performance in AZICs. • The N and S incorporation enhances the Zn2+ adsorption ability and charge transfer behavior. Emerging aqueous zinc–ion hybrid capacitors (AZICs) are considered a promising energy storage because of their superior electrochemical performance. The pore structure, suitable heteroatom content, and graphitization degree (GD) of carbon-based cathodes significantly influence the electrochemical performance of AZICs. The N, S dual-doped porous graphitic carbon materials (LC-750) with the combined characteristics of high GD (1.11) and large specific surface area (1678.38 m2 g−1) are successfully developed by a facile "killing two birds with one stone" strategy using K 3 Fe(C 2 O 4) 3 ·3H 2 O as the activating and graphitizing agent, and waste sponge (WS) and coal tar pitch (CTP) as the heteroatom and carbon resource, respectively. Results show that the LC-750 cathode displays high capacities of 185.3 and 95.2 mAh g−1 at 0.2 and 10 A g−1. Specifically, the assembled LC-750//Zn capacitor can offer a maximal energy density of 119.5 Wh kg−1, a power density of 20.3 kW kg−1, and a capacity retention of 87.8% after 15,000 cycles at 10 A g−1. Density functional theory simulations demonstrate that N and S dual-doping can promote the adsorption kinetics of Zn ions. This design strategy is a feasible and cost-effective method for the preparation of dual heteroatom-doped graphitic carbon electrodes, which enables recycling of WS and CTP into high-valued products. [ABSTRACT FROM AUTHOR]

Potassium ion batteries or capacitors are a promising technology for large-scale energy storage due to the abundant resource and low cost of potassium. However, the development of stable electrode materials with high capacity, capable rate ability, and excellent cycling stability remains a challenge. Herein, carbon dots modified reduced graphene oxides (LAP-rGO-CDs) are designed and synthesized via a rapid and green microwave-assisted method with l -Ascorbic acid 6-palmitate (LAP) as the reducing agent. LAP-rGO-CDs present enlarged interlayer spacing and faster ion transfer rate owing to the introducing of carbon dots. Serving as a potassium ion battery electrode, LAP-rGO-CDs showed a high specific capacity of 299 mAh g−1 at 1 A g−1 and excellent cycling stability. Moreover, a LAP-rGO-CDs//AC full carbon-based potassium ion capacitor is assembled and displays a maximum energy density of 119 Wh kg−1 and a power density of 5352 W kg−1. This work demonstrates the potential application of LAP-rGO-CDs for high-performance potassium ion storage. [Display omitted] [ABSTRACT FROM AUTHOR]

Binary metal niobium oxides can offer a higher specific capacity compared to niobium pentoxide (Nb 2 O 5) and thus are ideal anode candidates for lithium ion capacitors (LICs). However, their lower electronic conductivity limits their ability to achieve high energy and power densities. In this paper, one-dimensional (1D) copper niobate (CuNb 2 O 6) nanowires are successfully prepared by electrospinning technology and then immobilized on two-dimensional (2D) reduced graphene oxide (rGO) nanosheets to form a unique 1D nanowire/2D nanosheet CuNb 2 O 6 /rGO structure. The 1D/2D CuNb 2 O 6 /rGO electrode exhibits a high specific capacity of 312.2 mAh g−1 at 100 mA g−1 as the anode of LICs. The proposed Li+ storage mechanism of the CuNb 2 O 6 anode involves CuNb 2 O 6 decomposition into lithium niobate (Li 3 NbO 4) and copper (Cu) during the initial lithium insertion process. The intercalation-type Li 3 NbO 4 will further serve as the host to Li+ and the inactive Cu phase will act as a conductive network for electron transportation. Furthermore, the energy density of the assembled CuNb 2 O 6 /rGO//activated carbon (CuNb 2 O 6 /rGO//AC) device could achieve a value as high as 92.1 Wh kg−1 and could thus be considered as a possible alternative electrode material for high energy and power LICs. [ABSTRACT FROM AUTHOR]

• A PPy-rGO Janus-faced film is prepared through a facile and scalable method. • The PPy-rGO electrode reveals a ultra-high specific capacitances of 1380 mF cm−2. • The assembled PPy-rGO//PPy-rGO device delivers a high energy density of 31.95 Wh L−1. The flexible supercapacitors have attracted tremendous attention, but challenges still remain in seeking suitable electrode materials to enhance the energy density and other aspects. To this end, a unique Polypyrrole (PPy)-reduced graphene oxide (rGO) Janus-faced film is prepared through a facile and scalable method consisting of the deposition of graphene film on the surface of copper foil via a Cu||GO electrochemical cell followed by the self-assembly of PPy at the heterogeneous interface. Such a distinctive structure, in which the PPy layer acts as the source of high pseudo-capacitance, while the graphene layer is employed as the "high way" for rapid electron transport and as well as the strong π-π coupling effect between graphene and polymer nanosheets, endows the resultant electrode ultra-high specific capacitances (1380 mF cm−2 at 1 mA cm−2) and excellent rate capability (65.1% capacitance retention with the current density increases to 20 mA cm−2). Furthermore, the assembled PPy-rGO//PPy-rGO symmetric supercapacitors deliver a maximum energy density of 31.95 Wh L−1, remarkable cyclic stability (89.7% capacitance retention after 10,000 cycles) and superior mechanical property (82% capacitance retention after 8000 cycles under different bending conditions). [ABSTRACT FROM AUTHOR]

In this work, we design a three-dimensional (3D) strongly-coupled polyaniline/crosslinked carbon nanosheets (PANI/CCNs) composite using a facile in-situ chemical polymerization method. The PANI is uniformly and conformally covered on the thin graphene-like biomass-derived CCNs. The interconnected CCNs with high surface area and electrical conductivity can expose more active sites of PANI and enhance the interfacial electron transfer, which contributes to the improvement of specific capacitance and rate performance. The sheets-like PANI can introduce pseudocapacitance through the surface redox reactions on the surface. As a result, the PANI/CCNs composite electrode can reach high specific capacitance of 444 and 340 F g−1 at current densities of 0.1 and 5 A g−1, respectively. The assembled PANI/CCNs//PANI/CCNs symmetric supercapacitor can reach a high specific capacitance of 72.0 F g−1 at a current density of 0.1 A g−1. Moreover, the PANI/CCNs//PANI/CCNs symmetric cell exhibits a high energy density of 28.9 Wh kg−1 at a power density of 85.1 W kg−1, which is competitive in the aqueous PANI-based symmetric supercapacitors. • The willow catkin was adopted as the low-cost carbon source for the preparation of crosslinked carbon nanosheets. • The π–π stacking of PANI chains on the CCNs and the proton transfer from PANI to CCNs introduce abundant active sites. • The assembled symmetric supercapacitor delivers a high energy density of 28.9 Wh kg-1 at a power density of 85.1 W kg-1. [ABSTRACT FROM AUTHOR]

Binary transition metal sulfides are considered to be promising electrode materials for high-performance supercapacitors because of their ultrahigh electron conductivity and superior electrochemical activity compared to the unitary transition metal sulfides. In this work, copper cobalt sulfides nanowire arrays on nickel foam with different element ratios and porosities are prepared by using a two-step hydrothermal method, and their electrochemical performance is explored. Benefited from the high electrical conductivity, rich active sites and optimized microstructure, the optimized copper cobalt sulfides (CuCo 2 S 4) electrode can achieve a ultrahigh specific capacitance of 2446.6 F·g−1 at 1 A·g−1 and favorable rate performance. The asymmetric supercapacitor assembled with the CuCo 2 S 4 nanowire array and activated carbon (AC) electrodes displays a high energy density of 33.4 Wh·kg−1 at a power density of 751.5 W·kg−1 can be obtained. Additionally, the assembled asymmetric cell shows a favorable capacitance retention of 78% after charging and discharging for 10,000 cycles at a high current density of 4 A·g−1. • The CuCo 2 S 4 electrode achieves an ultrahigh specific capacitance of 2446 F·g−1 at 1 A·g−1. • The CuCo 2 S 4 electrode has unique microstructure and exhibits good rate performance. • The CuCo 2 S 4 /AC-ASC displays high energy density of 33.4 Wh·kg−1 at power density of 751.5 W·kg−1. [ABSTRACT FROM AUTHOR]

Highlight • A two-step hydrothermal strategy is adopted to transform Ni 3 [Fe(CN) 6 ] 2 to NiFe 2 O 4. • NiFe 2 O 4 @rGO slice is prepared as electrode for flexible symmetric supercapacitor. • NiFe 2 O 4 @rGO electrode shows excellent specific capacitance and cycling stability. Abstract A high working voltage and specific capacitance are vital for flexible solid-state symmetric supercapacitor (FSSC) devices to achieve decent energy densities with high power. In this paper, we report a 1.8 V FSSC based on NiFe 2 O 4 nanocubes anchored on reduced graphene oxide (rGO) cryogel electrode. Through surface protection by a free-standing three-dimensional cross-linked network structure, NiFe 2 O 4 converted from Ni 3 [Fe(CN) 6 ] 2 inhibits the original nanocube structure. Benefiting from the synergistic effects between NiFe 2 O 4 nanocubes and graphene nanosheets, the newly synthesized NiFe 2 O 4 @rGO hybrid electrode delivers a high charge storage capacity (488 F g−1 at a constant current density of 1 A g−1), excellent rate ability and cycling performance (89.8% of the initial capacitance value after 10,000 cycles). In addition, NiFe 2 O 4 @rGO FSSC has been assembled and exhibits stable behavior at bend state, as well as high energy density of 62.5 Wh kg−1, and long cycle life (93.2% of the initial capacitance value after 6000 cycles). The proposed strategy for controlling the design and synthesis of NiFe 2 O 4 @rGO nanostructures provides promise for the development of high performance electrode in advanced energy storage devices. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Unique nanostructure, high electrical conductivity, satisfactory energy density, and extraordinary cycling stability are important evaluation criteria for high-efficient energy storage devices. Herein, Fe 3 O 4 nanospheres are successfully in situ decorated on graphene nanosheets through an environmentally benign and facile solvothermal procedure. When utilized as an electrode for supercapacitor, the graphene/Fe 3 O 4 nanocomposite exhibits a notably enhanced specific capacity (268 F·g−1 at 2 mV·s−1) and remarkable cycling performance with 98.9% capacity retention after 10,000 cycles. Furthermore, the fabricated graphene/MnO 2 //graphene/Fe 3 O 4 asymmetric supercapacitor device displays a desirable energy density (87.6 Wh·kg−1) and superior cycling stability (93.1% capacity retention after 10,000 cycles). [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Flexible supercapacitor plays a progressively more important part in power source for smart electronic devices and how to enhance its energy density is the urgent issue to be addressed. Hence, a hybrid electrode of Polypyrrole@reduced graphene oxide hydrogel (PPy@rGOH) is synthesized via a combine hydrothermal treatment of GO solution to assemble hydrogel and subsequently in-situ electropolymerization preparation of PPy on the surface of graphene. Through controlling the time of electropolymerization, the resultant PPy@rGOH-20 s with high specific surface area exhibits an excellent specific capacitance of 340 F g−1 at a current density of 1 A g−1 and superior cycling stability of 87.4% capacitance retention after 10,000 charging/discharging cycles at 3 A g−1 in 1 M KNO 3. The assembled flexible asymmetric supercapacitor (FASC) by employing the PPy@rGOH-20s as positive electrode and pure rGOH as negative electrode presents a maximum operational voltage window of 1.6 V and high energy density of 46.9 W h kg−1, which is higher than polymer/carbon-based supercapacitors previously reported. [ABSTRACT FROM AUTHOR]

Abstract In this work, activated carbon tube bundles (ACTBs) with porous hollow structure are prepared using dandelion fluffs as precursors. The open-framework porous structure of the ACTBs contributes to large specific surface area and enhanced electrochemical performances. Then the ACTBs are further modified with polyaniline (PANI) using the in-situ polymerization method, the unique hollow tube structure of the ACTBs effectively increases the growth area for the PANI. The PANI modified ACTBs (PANI/ACTBs) composite exhibits an excellent rate performance due to the highly retained porous hollow tube structure, which promotes the electrolyte ions diffusion and electron transport. Meanwhile, the ACTBs and PANI/ACTBs serve as the cathode and anode electrode materials for asymmetric supercapacitor, respectively. As a result, the asymmetric supercapacitor displays a high energy density of 42 Wh kg−1 and a capable cycling stability. These results demonstrate that the PANI/ACTBs composite is a promising electrode material for the energy storage devices. Graphical abstract Image 1 Highlights • The porous structure of the ACTBs contributes to the enhancement of the specific surface area and cycling stability. • The ACTBs can solve the aggregation problem and provide more space for the volume changes of the PANI particles. • The PANI/ACTBs exhibits high capacitance and the good cycling stability due to the combined advantages of PANI and ACTBs. • The PANI/ACTBs composite exhibits high energy density of 42 Wh kg−1. [ABSTRACT FROM AUTHOR]

A simple hydrothermal route is designed to decorate NiCo 2 S 4 nanoparticles on the surface of N-doped carbon nanotubes to form a coaxial composite (NiCo 2 S 4 @NCNT). Inherited the high electrical conductivity from the NCNT and high capacitive performance of NiCo 2 S 4 , the optimized NiCo 2 S 4 @NCNT composite could significantly reduce the contact resistance and effectively increase the transfer rate of ion and electron and thus benefit for its electrochemical performance enhancement. When employed as a battery-type supercapacitor electrode, the NiCo 2 S 4 @NCNT composite exhibits a high capacitance up to 783.5 C g −1 at 1 A g −1 and as well as rate performance (74.6% retention with the current density increases from 1 to 50 A g −1 ). Coupled with activated carbon (AC) negative electrode, the as-assembled hydride supercapacitor delivers a maximum energy density of 49.75 Wh kg −1 at a power density of 774.65 W kg −1 , as well as 88.9% capacitance retained after 3000 cycles at a current density of 10 A g −1 . These above results demonstrate the enormous potential of NiCo 2 S 4 @NCNT in the development of hybrid supercapacitors. [ABSTRACT FROM AUTHOR]

Flexible solid-state supercapacitor (FSSC) holds great promise as power source to supply the next generation of portable and wearable electronics. Assembling asymmetric supercapacitor constructed with broadening cell voltage ( V ) is the promising way to increase the energy density. However, the imparity reaction kinetics between EDLC and pseudocapacitive materials will further lead to inferior power density. Hence, to pursue higher working voltage and energy density, a hybrid configuration of cobalt hexacyanoferrate/reduced graphene oxide hydrogels (PB-Co/rGOH) is prepared through a one-pot hydrothermal method. With highly interconnected 3D network structure, excellent mechanical robustness and the synergistic effects between the graphene and PB-Co, the resultant PB-Co/rGOH exhibits a high specific capacitance of 220 F g −1 and well cycle stability (83% capacitance retention after 10,000 cycles at 5 A g −1 ). Moreover, the assembled PB-Co/rGOH//PB-Co/rGOH symmetric flexibly solid-state supercapacitor exhibits an amazing higher working voltage of 2.0 V and a remarkable energy density of 57.5 Wh kg −1 , which is comparable with that of Ni/MH batteries (60–120 Wh kg −1 ). These excellent electrochemical performances of the hybrid electrode provide a rational design strategy for developing supercapacitors with high energy density. [ABSTRACT FROM AUTHOR]

The flexible solid-state supercapacitor (FSSC) has attracted many attentions due to its feature of high power density with stable cycling performance, as well as lightweight and flexible features and is expected as an ideal candidate power supply for portable and wearable electronics devices. In general, the electrode plays an important role in determining the overall performance of the FSSC. Therefore, to meet the requirement of practical applications, a simple, facile and environment friendly strategy to prepare deformable/flexible electrodes with high energy density is the target issue to be considered. Herein, we report a generalized “soaking-recrystallization-calcination” method to enhance the capacitance performance of commercialized carbon fiber cloth. Thanks to the in-situ etching process to increase the surface area and the synchronous heteroatom doping to induce pseudocapacitive behavior, the resultant activated carbon fiber cloth sample exhibits an ultra-high areal capacitance up to 362 mF cm −2 , is about 1448 fold enhancement than that of fresh carbon fiber cloth calcined at 750 °C. Meanwhile, the assembled FSSC based on the activated carbon fiber cloth exhibits a maximum volumetric energy density of 0.35 mWh cm −3 and gravimetric energy density of 0.84 Wh kg −1 . Such results represent a novel and promising direction to prepare high performance flexible electrode for FSSC application. [ABSTRACT FROM AUTHOR]

Spinel LiMn 2 O 4 has been prepared by a facile hydrothermal procedure and the prepared LiMn 2 O 4 exhibits superior electrochemical performance, such as high specific capacitance (409 F g −1 at 2 mV s −1 ) and excellent rate capability (85% retention at 100 mV s −1 ). In order to achieve high energy and power densities, a high-voltage asymmetric supercapacitor (ASC) is successfully assembled using the as-prepared LiMn 2 O 4 as the positive electrode and nitrogen-doped graphene/porous carbon composite as the negative electrode in a Li 2 SO 4 aqueous electrolyte. The optimized ASC delivers a high specific energy of up to 44.3 Wh kg −1 at a specific power of 595 W kg −1 with an output voltage of 1.8 V based on the total weight of the active electrode materials. This novel strategy provides a promising route to design high-performance supercapacitors with high energy density for next-generation storage systems. [ABSTRACT FROM AUTHOR]

• α-MnSe Nanosheets are prepared via a facile hydrothermal method. • The effect of reaction time on electrochemical performance is investigated. • The α-MnSe electrode delivers a high capacity of 88.3 mAh g−1 at 1 A g−1. • The asymmetric supercapacitor exhibits a high energy density of 39.3 Wh kg−1. Transition metal selenides are regarded as emerging materials for energy storage devices because of their good electrical conductivity and electrochemical activity. Here, a binder-free ultrathin α-MnSe nanosheets electrode is prepared and the supercapacitor performance is comprehensively explored. Due to the increased active sites, enlarged contact area for electrolyte, as well as shorten ions diffusion pathway, the prepared electrode delivers high capacity of 88.3 mAh g−1 at 1 A g−1, good rate capability, and long-term durability (91% remain after 5000 cycles). Moreover, the asymmetric supercapacitor, fabricated by α-MnSe anode and active carbon cathode, displays a high energy density of 39.3 Wh kg−1 at a power density of 0.92 kW kg−1 and satisfying cycle performance. This study demonstrates that the binder-free α-MnSe electrode holds great promise for supercapacitor. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogen-rich biomass carbon (N-CHC) was prepared by urea etching method. • N-CHC exhibits excellent capacity and rate performance as a K+ half-cell anode. • Large specific surface area, lots of defects and heteroatoms are key advantages. • The hybrid capacitor composed of N-CHC and AC exhibits high energy and power density. Potassium ion hybrid capacitors have the advantages of high energy density, high power density, and low cost, and are expected to replace expensive lithium ion storage devices in large-scale applications. Here, an innovative nitrogen-rich biomass carbon (N-CHC) is prepared using urea as the etchant and hemp core as the raw material, which has a high specific surface area of 1185.3 m2 g−1 and nitrogen content of 8.56%. In addition, it shows a capacity of 442.4 mAh g−1 as a potassium ion half-cell anode at 30 mA g−1. Even under the high current test of 2000 mA g−1, N-CHC also shows excellent performance (175.0 mAh g−1). Further, the good rate performance is attributed to the large-scale capacitance control by analyzing reaction process kinetics. And the constant current intermittent titration technique (GITT) results show that N-CHC has a larger K+ diffusion coefficient than unetched biomass carbon. The maximum energy density of the full carbon-based hybrid capacitor composed of N-CHC anode and activated carbon cathode is 127.36 Wh kg−1, and the maximum power density is 2371 W kg−1. [ABSTRACT FROM AUTHOR]

Developing novel materials with rational structures and excellent electrical conductivity is vitally important for energy storage devices. Herein, hollow cobalt molybdenum selenide (Co–Mo–Se) nanosheet arrays are fabricated via a self-sacrificing template method and selenization process, where cobalt-organic framework serves as the template. Benefiting from unique hollow nanoarrays structure, the Co–Mo–Se electrode offers rich electroactive sites, large accessible regions for electrolyte, and short ions diffusion pathways. Additionally, it is observed that the Co–Mo–Se possesses a low charge transfer resistance owing to the intrinsic metallicity. As a result, the Co–Mo–Se electrode exhibits favorable energy storage properties, including high capacity (221.7 mAh g−1), good rate property, and outstanding stability (95% after 8000 cycles). More importantly, the assembled Co–Mo–Se//active carbon (AC) achieves high energy density (44.7 Wh kg−1) and remarkable durability. Notably, two hybrid devices connected in series successfully power an electronic watch for 70 min, demonstrating its practical applicability. These results indicate that the synthesized hollow Co–Mo–Se nanosheet arrays have promising applications as electrode materials for high-performance energy storage devices. • Co-MOF was employed as template to obtain hollow Co–Mo–Se nanosheet arrays. • The Co–Mo–Se delivers a specific capacity of 221.7 mAh g−1 at 1 A g−1. • The ion exchange/etching method was applied in this work. • The asymmetric supercapacitor delivers high energy and power densities. [ABSTRACT FROM AUTHOR]

• CoSe 2 /RGO composite were prepared via a facile microwave assisted method. • The effects of RGO content on electrochemical performance were investigated. • The CoSe 2 /RGO-3 electrode delivers high capacitance of 761 F g−1 at 1 A g−1. • The CoSe 2 /RGO-3//AC exhibits high energy density of 43.1 Wh kg−1 at 800 W kg−1. The composites composed of metal selenides and carbonaceous materials have revealed enormous potential in varied applications. Herein, CoSe 2 /reduced graphene oxide (CoSe 2 /RGO) composites are prepared by a low-cost and efficient microwave assisted method. The effects of RGO proportion on crystalline structure, microstructure and energy storage capacity are explored. Benefiting from the good electrical conductivity and reasonable RGO content, the CoSe 2 /RGO sample with 35.2 wt% RGO reveals an excellent specific capacitance of 761 F g−1 as well as outstanding durability. More importantly, we construct an all solid-state hybrid supercapacitor (CoSe 2 /RGO//active carbon) to broaden the voltage window, resulting in an enhanced energy density (43.1 Wh kg−1). The hybrid device presents a favorable durability with 10% capacity drop after 10,000 cycles. In addition, the practical applicability of asymmetric device is confirmed by powering a blue light emitting diode (LED) for more than 10 mins. This work presents a simple, effective, and reasonable construct strategy to synthesize composites of selenides and RGO for charge storage application. [ABSTRACT FROM AUTHOR]

Bimetallic metal selenides have gained increasing attention as potential electrode materials for energy storage systems owing to good electrical conductivity and superior electrochemical activity. Herein, the Ni x Co y Se 2 (x+y=1) electrodes are prepared by a facile and rapid electrodeposition process. The electrochemical performance is optimized via adjusting the ratio of Co and Ni. It is turned out that equivalent Co and Ni in the composite (Ni 1/2 Co 1/2 Se 2) shows the best supercapacitor performance, including high specific capacity (166.1 mAh g−1) and long-term stability. Moreover, Density Functional Theory (DFT) calculation confirms the covalent interaction between nickel and cobalt, implying the existence of synergistic effect. To assess the practical value of the rationally designed Ni 1/2 Co 1/2 Se 2 electrode material, an asymmetric supercapacitor device is fabricated (Ni 1/2 Co 1/2 Se 2 //AC), which delivers a high energy density of 46.0 Wh kg−1 at 1141 W kg−1, coupled with 9.8% capacity loss after 10000 cycles. Notably, the low-voltage setups (LED and electric fan) can be easily activated by two devices in series, further demonstrating the great potential for practical application of Ni 1/2 Co 1/2 Se 2 electrode. [ABSTRACT FROM AUTHOR]

• Bimetallic (Ni,Mo)S 2 was synthesized through a two-step solvothermal approach. • The (Ni,Mo)S 2 /G composite exhibits high specific capacity of 951 C g−1. • The ASC device shows a ultrahigh energy density of 84.5 Wh kg−1. Thanks to their high electrical conductivity, electrochemical stability and activity, transition metal sulfides have been widely designed and developed for supercapacitors with excellent electrochemical performances. Herein, we report the NiS 2 /MoS 2 mixed phases with abundant exposed active edge sites decorated on graphene nanosheets (named as (Ni,Mo)S 2 /G) through a facile two-step hydrothermal approach. Benefitting from its unique chemical property and structure, the as-prepared (Ni,Mo)S 2 /G composite possesses impressive electrochemical performances as electrodes of battery-type supercapacitors in 2 M KOH, such as high specific capacity of 951 C g−1 (2379 F g−1) at 1 A g−1 with superb rate capability (60.7% at 100 A g−1). Additionally, the asymmetric supercapacitor (ASC) device assembled based on the active edge site-enriched (Ni,Mo)S 2 /G as positive electrode and nitrogen-doped porous graphene as negative electrode displays an ultrahigh energy density of 84.5 Wh kg−1, superior to those of the Ni- and Mo-based ASCs in aqueous electrolytes reported so far. Such novel strategy may hold great promise for exploring other polymetallic sulfides with abundant exposed active edge sites for energy storage and conversion. [ABSTRACT FROM AUTHOR]

• The PTC-S as anode has an outstanding performance in 0.5 M LiCl + 0.5 M MgCl 2 aqueous solution. • The PTC-S exhibits a good rate ability and cycling stability. • PTC-S‖LiMn 2 O 4 has a high capacity and excellent cycling stability. Aqueous batteries are appealing for large-scale storage applications, due to their high safety level, low cost, and excellent durability. In this study, we reported a new anode material, namely sulfur perylene-3,4,9,10-tetracarboxylate (PTC-S), which is more stable than other electrode materials used in aqueous Mg-Li ion batteries. When PTC-S is used as the anode in 0.5 M MgCl 2 + 0.5 M LiCl with a current density of 50 mA g−1, the discharge specific capacity is 287.3 mAh g−1 at the initial cycle and the capacity retention rate is still close to 100% at over 1000 cycles. The monomer structural material conjugated with bifunctional groups can provide the space for the intercalation of Mg2+ and Li+ at the same time, shorten the ion transmission path and accelerate the transmission speed of metal ions in the electrode. In order to develop aqueous battery as quickly as possible, LiMn 2 O 4 and PTC-S are used as cathode and anode materials, respectively, in a dual-ion salt aqueous battery. The PTC-S‖LiMn 2 O 4 battery exhibits a high capacity and an excellent cycling stability performance in aqueous Mg-Li ion battery. The battery has a high capacity performance of 240.0 mAh g−1 at a voltage ranging from 0.0 V to 1.8 V, as well as a high specific energy density of 172.8 Wh kg−1 and remarkable cycling stability. PTC-S in 0.5 M MgCl 2 electrolyte has a current density of 100 mA g−1, a specific discharge capacity of 203 mAh g−1 and a first-cycle Coulomb efficiency close to 100%. Under the same test conditions, the discharge specific capacity is higher than that of the perylene-3,4,9,10-tetracarboxylic dihydride (PTCI) electrode (101 mAh g−1), and the capacity retention rate is increased by 30.4%. [ABSTRACT FROM AUTHOR]

• NiNb 2 O 6 @NC-2 hollow nanoparticles is used as rate capability anode for LICs. • The NiNb 2 O 6 @NC-2 exhibits a high specific capacity of 435.8 mAh g−1 at 50 mA g−1. • NiNb 2 O 6 decomposes into Ni metal and Li x Nb 2 O 6 in the 1st charge/discharge process. • The NiNb 2 O 6 @NC//AC LICs has a maximum energy density of 123.9 Wh kg−1. Searching for anode materials with fast Li+ intercalation kinetics to mitigate the dynamic imbalance with the rapid capacitive cathode is the fundamental strategy to achieve high energy-power density of Li-ion capacitors (LICs). Hence, NiNb 2 O 6 hollow nanoparticles are first synthesized by hydrothermal method and then sealed with a protective N-doped carbon shell to achieve the target NiNb 2 O 6 @NC composite. As the anode of LICs, the NiNb 2 O 6 @NC sample exhibits a high capacity of 435.8 mAh g−1 at 50 mA g−1 and excellent rate performance of 47.8% capacity retention with the current density increased to 2 A g−1. The lithium storage mechanism of NiNb 2 O 6 is proposed as a combined conversion reaction and an intercalation reaction, which the NiNb 2 O 6 decomposes into Ni metal and Li x Nb 2 O 5 during the 1st discharge/charge process. The irreversible Ni would not contribute to the reversible capacity and will improve the electric conductivity for fast transport of electrons and the Li x Nb 2 O 5 will act as the host for lithium ions by means of the intercalation mechanism. Furthermore, the assembled NiNb 2 O 6 @NC//activated carbon LICs exhibit a maximum energy density of 123.9 Wh kg−1 and the capacity retention reaches 86.1% after 5000 cycles. The superior electrochemical performances indicate that the rationally-designed NiNb 2 O 6 @NC is expected to be a potential anode material for LICs. [ABSTRACT FROM AUTHOR]

Flexible electrochemical energy storage devices have great potential in wearable and portable electronic devices. However, their practical applications have been deferred by mechanical damages such as repeated stretching, bending and squeezing. Self-healing hydrogel electrolytes can automatically repair such physical damages and maintain good electric contact at electrode/electrolyte interface. Herein, we report a hydrogel electrolyte with excellent tensile properties and good conductivity under large strain/stress. A solid state supercapacitor was further demonstrated, showing a high energy density of 21.3 Wh kg-1 at a power density of 350 W kg-1. The as-fabricated supercapacitor possesses good stretchability, with a 68% of retention of its initial capacitance after 40 breaking/healing cycles. The excellent self-healing capability of the hydrogel electrolyte can be attributed to the presence of hydrogen bonds and molecular chain fluidity within its structural motif. Our work provides promising routes towards developing new self-healing solid-state electrolytes for next-generation electrochemical energy storage and conversion applications with good performance and high safety. [ABSTRACT FROM AUTHOR]

This work presents a novel method for loading phosphorus nanoparticles by gas deposition. A large amount of nano phosphorus is loaded on the carbon matrix by the reaction of phosphine gas heating. The carbon is obtained by carbonization of hemp and has a natural porous structure. The combination of phosphorus and carbon in the form of C–O–P has better stability. The product obtained a stable capacity of 463 mAh/g at 0.04 A/g. There was still a reversible capacity of 270 mAh/g after continuous operation for 6 months at a high current density of 1 A/g, and the capacity retention rate was 96.7%. The excellent cyclic stability is due to new methods of phosphorus deposition. It can reach 10 times the running time of the same type of battery, which provides a new idea for preparing phosphor-doped electrode materials. Assembled into a potassium ion capacitor, an energy density of 294.2 Wh/kg can be obtained. [ABSTRACT FROM AUTHOR]

• Ultrathin in-plane 1T-2H MoS 2 heterostructures are coaxially arrayed on 3D CFs. • The 1T-2H ultrathin heterostructures exhibit surprising structure stability. • Our ASC device exhibits an ultrahigh energy density of 81.4 Wh kg−1. Metallic 1T MoS 2 is a promising anode candidate for supercapacitors due to its intrinsically excellent electrical conductivity and high electrochemical activity. However, it is quite unstable and hard to be massively synthesized through common methods. Herein, structurally stable ultrathin (1–3 layers) in-plane 1T-2H MoS 2 heterostructures have been rationally modulated and coaxially aligned on three-dimensional carbon nanofibers (MoS 2 /CF) through a facile hydrothermal approach for supercapacitors and electrocatalysis. Benefiting from the unique heterostructure, the MoS 2 /CF composite shows amazing stability with no obvious change after being stored in air for over 36 months. In addition, it presents high specific capacitance of 310 F g−1 and remarkable rate capability of 78% at 100 mV s−1. The fabricated asymmetric supercapacitor delivers an impressive energy density of 81.4 Wh kg−‍‍‍‍‍1 in 1 M Na 2 SO 4 solution attributed to the high specific capacitance and large operating voltage range of 2 V. Moreover, the MoS 2 /CF composite also demonstrates enhanced electrocatalytic activity for hydrogen evolution reaction with a low overpotential of 194 mV at 10 mA cm−2. The work may promote the developments of high-performance bifunctional energy conversion and storage systems in future. [ABSTRACT FROM AUTHOR]

• The human hair with high elasticity capable can serve as a promising flexible supporter for the electrode. • The reduced graphene oxide nanosheets can effectively improve the electrical conductivity of the electrode. • The Ni(OH) 2 nanoribbon-intercalated rGO nanosheets shows an interconnected porous structure. • The solid-state flexible supercapacitor delivers high energy density and good cycling stability. The demands for wearable energy storage devices keep growing and novel flexible electrode materials and facile prepared methods for these devices are crucial and attractive. In this work, human hair fiber is employed as the flexible fiber-based material due to the high utilization values of low cost, controllable length and high elasticity capable. Herein, an effective and hazard-free microwave-assisted method is reported to develop superelastic reduced graphene oxide coating human hair (rGO@Hh) to achieve conductive and high-strength fibrous electrode. With the braided rGO@Hh fibers, nickel hydroxide nanoribbon-intercalated rGO nanosheets (Ni(OH) 2 /rGO@Hh) are further prepared through microwave radiation treatment, which shows an interconnected porous structure with outstanding electrochemical performances of high specific capacitance (316 F g−1 at 1 A g−1) and good cycling performance. Moreover, a solid-state fiber-based asymmetric supercapacitor (FASC) is assembled with rGO@Hh fibers and Ni(OH) 2 /rGO@Hh fibers as negative and positive electrodes, which demonstrates a high energy of 27.6 Wh kg−1 and a power density of 699 W kg−1, respectively. The FASC also can be further used for numerous electronic products, presenting its prospect for portable wearable devices with high tensile strength and excellent performances. [ABSTRACT FROM AUTHOR]

NiS 2 is a promising anode material for sodium-ion batteries (SIBs) and capacitors (SICs). However, the sluggish Na+ diffusion and large volume change of bulk NiS 2 during sodiation/de-sodiation lead to poor rate capability and fast capacity decay, limiting its practical application. Herein, we design and prepare well-oriented NiS 2 nanosheets on porous carbon microtubes (denoted as NiS 2 /pCMT) as a novel anode material for SIBs/SHCs. The unique porous hollow carbon tubes and NiS 2 nanosheets can well relieve the repeated stress/strain and maintain the structural integrity of the composite anode during long-term charging/discharging. As a confirmation, a modelled SHC is constructed by using the NiS 2 /pCMT composite as anode and coupling with an activated carbon cathode, delivering a high energy density of 136 Wh kg−1 and good cycling stability. The first-principles density functional theory (DFT) calculations confirm that the NiS 2 nanosheets surface has a high chemical affinity towards Na+ ions, promising the concentration of Na+ ion on/nearby the surface for fast redox reactions during sodiation/de-sodiation of NiS 2. This work provides some new insights for the design and fabrication novel composite electrode materials for applications in beyond lithium-ion batteries/capacitors. • The carbon microtubes have unique tubular structure and good conductivity. • NiS 2 nanosheets uniformly grow on both sides of the carbon microtubes. • The layered NiS 2 nanosheets facilitate the intercalation of the Na+ ions. • The sodium-ion hybrid capacitor delivers high energy and power densities. [ABSTRACT FROM AUTHOR]

Lithium-ion capacitors (LICs) by combines the virtues of lithium-ion batteries and supercapacitor have received intensive attention owing to their preeminent energy density, outstanding power density and uncompromised cycle life. However, the practical application of LICs has been greatly hampered by the lack of efficient anode materials. Herein, a facile strategy including hydrothermal reaction and subsequent thermal calcination has been carefully designed for constructing MnO porous spheres with a N-doped carbon coated layer (MnO@N-C). The resultant MnO@N-C electrode delivers a high capacity of 903 mA h g−1 and excellent cyclic performance with 96.2% capacity retention after 1000 cycles. Furthermore, the assembled MnO@N-C//AC LICs displays an excellent energy density of 125.3 Wh kg−1 and superior power density of 19.9 KW kg−1, as well as long cyclic lifetime of 5000 cycles with 83.2% capacity retention, outperforming those of recently reported metal oxide based LICs. Image 1 • MnO@N-C is obtained through a hydrothermal reaction and subsequent thermal calcination. • The MnO@N-C displays a high capacity of 903 mA h g−1 and outstanding stability with 96.2% capacity retention. • The assembled MnO@N-C//AC LICs reveals an excellent energy density of 125.3 Wh kg−1. [ABSTRACT FROM AUTHOR]