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In this article, ZnCo 2 O 4 nanowires deposited with two kinds of typical layered double hydroxides (Ni–Al,Co–Al LDH) are developed via scalable method. Two materials all display core–shell hierarchical structure. High specific capacitance of 2041 F g−1 and 1586 F g−1 are obtained for ZnCo 2 O 4 @Co–Al LDH and ZnCo 2 O 4 @Ni–Al LDH,respectively. Combining with active surface and synergistic effect, the role of hierarchical structure in enhancing performance is revealed. Moreover, two all solid state supercapacitors based on fabricated materials as positive electrodes, activated carbon as negative electrodes and PVA–KOH as polymer electrolyte are assembled. The maximum power and energy densities of ZnCo 2 O 4 @Co–Al LDH//AC are 6200 W kg−1 and 50.1 Wh kg−1, respectively. While the power and energy densities of ZnCo 2 O 4 @Ni–Al LDH//AC are 3400 W kg−1 and 27.8 Wh kg−1. At last, an energy storage–conversion system, based on solar cell as input device and assembled asymmetric supercapacitor ZnCo 2 O 4 @Co–Al LDH//AC as output device, is integrated as a self–sustaining power device, indicating its potential in practical applications. In this article, ZnCo 2 O 4 nanowires deposited with two kinds of typical layered double hydroxides (LDHs) are developed via scalable method. Combining with active surface and synergistic effect, the role of hierarchical structure of each material in enhancing performance is revealed. Moreover, an energy storage–conversion system, based on solar cell as input device and assembled asymmetric supercapacitor as output device, is integrated as a self–sustaining power device, further indicating its potential in practical applications. Image 1 [ABSTRACT FROM AUTHOR]

[Display omitted] • OMC@NiO/Ni is synthesized via solvothermal reaction and subsequent calcination treatment. • "Trunk-leaf vein" structure endows OMC@NiO/Ni with superior electrochemical performance. • An asymmetric supercapacitor based on OMC@NiO/Ni and rGO/VO x as positive and negative electrodes respectively, is assembled. Supercapacitors are sustainable energy storage devices with the characteristics of high power density, long life span and ultrafast charge-discharge time. Herein, considering low conductivity of NiO and inspired by the "trunk-leaf vein" structure, mesoporous carbon and nickel dots are introduced into structure reacting as electron scaffold via facile hydrothermal and annealing procedures. Special hierarchical structure is obtained with oxygen modified mesoporous carbon (OMC) as core and NiO sheets as core accompanying with metallic nickel dots deposited on NiO sheets. Such "trunk-leaf vein" architecture can effectively ensure more active sites contacting with electrolyte, furthermore provide conductive scaffolds for electron transport. As expected, the OMC@NiO/Ni exhibits high specific capacitance of 651.3 F g−1 at 2 A g−1 and superior cycling life of 92.2% after 4000 cycles. Moreover, a novel negative electrode rGO/VO x is synthesized ascribe to the superior capacitance and life span. At last, an asymmetric device is assembled using OMC@NiO/Ni as positive electrode and rGO/VO x as negative electrode, which delivers maximum energy density of 44.3 Wh kg−1, high power density of 12,000 W kg−1 and excellent cycling life of 94.5% after 5000 cycles. The high performance of OMC@NiO/Ni renders it a potential material for energy storage-conversion equipments. [ABSTRACT FROM AUTHOR]

Summary: Doping Mn element into host material is an efficient approach to enhance the specific capacitance and cycling stability of supercapacitor. In this aspect, we fabricate Co‐Mn LDHs (CMLs) hollow polyhedron generated from ZIF‐67 via a template sacrifice method. Controllable doping of Mn element with gradient contents on the effect of electrochemical performance are investigated in detail. Moreover, in order to assemble a hybrid supercapacitor with superior energy and power output, a negative electrode based on MXene/rGO/V10O24 is synthesized considering the integration of EDLC and pseudocapacitance. As expected, the asymmetric supercapacitor of CMLs‐0.53//MXene/rGO/V10O24 delivers high energy density of 44.4 Wh kg−1, maximum power density of 12 750 W kg−1 and superior cycling life (91.6% capacitance retention after cycling 10 000 cycles). The special idea on the construction of CMLs with hollow structure can offer new insight to resolve the complicated steps during preparation procedure. The results also indicated that the device based on CMLs‐0.53 and MXene/rGO/V10O24 is a good candidate in the utilization of energy storage and conversion system in the future. [ABSTRACT FROM AUTHOR]

Abstract: Ni(OH)2 nanosheets are directly grown on nickel foam by a simple template-free growth process. Their microstructure and surface morphology are studied by X-ray diffraction spectroscopy and scanning electron microscopy. The XRD and SEM results show that Ni(OH)2 has a β-phase structure and covers the nickel foam skeleton with nanosheets. This β-Ni(OH)2/Ni-foam electrode exhibits a high specific electric quantity of 790.3 C g−1 approaching the theoretical value (1040.6 C g−1) and high electrochemical activity. Asymmetric supercapacitor has been fabricated successfully using β-Ni(OH)2/Ni-foam nanosheets as positive electrode and activated carbon as negative electrode in a KOH aqueous electrolyte. The electrochemical capacitances of this supercapacitor are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. An asymmetric supercapacitor AC/6 mol L−1 KOH/β-Ni(OH)2/Ni-foam could be cycled reversibly in the high-voltage region of 0–1.6 V and displays intriguing performances with a specific capacitance of 105.8 F g−1 and high energy density of 36.2 W h kg−1. Importantly, this asymmetric supercapacitor device exhibits an excellent long cycle life along with 92% specific capacitance retained after 1000 cycles. [Copyright &y& Elsevier]

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]

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]

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]

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]

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]

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]

In this work, for the first time, we design a high-energy-density double-chamber capacitor which consists of the cathode chamber (polyaniline@carbon fiber cloth electrode in HCl/FeCl 3 solution), anion-exchange membrane and the anode chamber (polyaniline@carbon fiber cloth electrode in HCl/FeCl 2 solution). Since the redox state of polyaniline can be continuously altered by the external potential during charging and discharging process, the addition of FeCl 3 (or FeCl 2 ) in the electrolyte works as chemical oxidant (or reductant) to oxidize (or reduce) the reduced (or oxidized) polyaniline to offer extended capacitance. Results show the double-chamber supercapacitor has a high area specific capacitance of 1.22 F cm −2 and an energy density of 108.44 μWh cm −2 , which are ∼3.5 times as large as those of the conventional single-chamber capacitor (0.35 F cm −2 / 31.11 μWh cm −2 ). This work demonstrates an innovative strategy by incorporating supercapacitor with fuel cell to improve the 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]

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]

• 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]

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]

• 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]

• 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]

• 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]

• 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]

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]

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]

MnO 2 is regarded as an ideal material of supercapacitor since its low-cost, environment friendly and high specific capacitance but hindered by its poor electrical conductivity. Developing a composite electrode that combines nano-structure MnO 2 with a conductive skeleton such as carbon materials could make up for the shortcomings. Here, porous activated carbon (PAC) is synthesized by using low-cost wheat bran as biomass carbon precursor and a mixture of NaCl/ZnCl 2 as combined solvent-porogen. The resultant PAC sample presents a hierarchical porous structure and large specific surface area up to 1058 m2 g−1. Afterwards, MnO 2 nanosheets decorated PAC (MnO 2 @PAC) is prepared via an in-situ hydrothermal deposition. It is a key finding that the ion/electron transfer kinetics of MnO 2 @PAC could be effectively improved by the addition of hierarchical porous carbon. Thus, the MnO 2 @PAC electrode displays a high specific capacitance (258 F g−1 at 1 A g−1) and superior rate performance (82.8% capacitance retention with the current density ranging from 1 A g−1 to 20 A g−1). Furthermore, an asymmetric supercapacitor is assembled by employing the MnO 2 @PAC as the positive electrode and PAC as negative electrode, which exhibits a high energy density of 32.6 Wh kg−1 and as well as 93.6% capacity retention at over 10,000 charge/discharge cycles. • Porous activated carbon (PAC) is synthesized by a controllable molten salt method. • MnO 2 nanosheets were deposited on the PAC through a simple hydrothermal reaction. • The MnO 2 @PAC displays high specific capacitance and outstanding stability. • The PAC//MnO 2 @PAC asymmetric supercapacitor exhibits energy density of 32.6 Wh kg−1. [ABSTRACT FROM AUTHOR]

Developing advanced supercapacitors with both high areal and volumetric energy densities remains challenging. In this work, self‐supported, compact carbon composite electrodes are designed with tunable thickness using 3D printing technology for high‐energy‐density supercapacitors. The 3D carbon composite electrodes are composed of the closely stacked and aligned active carbon/carbon nanotube/reduced graphene oxide (AC/CNT/rGO) composite filaments. The AC microparticles are uniformly embedded in the wrinkled CNT/rGO conductive networks without using polymer binders, which contributes to the formation of abundant open and hierarchical pores. The 3D‐printed ultrathick AC/CNT/rGO composite electrode (ten layers) features high areal and volumetric mass loadings of 56.9 mg cm−2 and 256.3 mg cm−3, respectively. The symmetric cell assembled with the 3D‐printed thin GO separator and ultrathick AC/CNT/rGO electrodes can possess both high areal and volumetric capacitances of 4.56 F cm−2 and 10.28 F cm−3, respectively. Correspondingly, the assembled ultrathick and compact symmetric cell achieves high areal and volumetric energy densities of 0.63 mWh cm−2 and 1.43 mWh cm−3, respectively. The all‐component extrusion‐based 3D printing offers a promising strategy for the fabrication of multiscale and multidimensional structures of various high‐energy‐density electrochemical energy storage devices. The all‐graphene‐oxide (GO)‐based symmetric supercapacitor is assembled with a thin GO separator and compact active carbon/carbon nanotube/reduced graphene oxide composite electrodes with tunable thickness, which are fabricated using the advanced extrusion‐based 3D printing technology. The 3D‐printed ultrathick and compact symmetric supercapacitor with a high mass loading can achieve both high areal and volumetric energy densities. [ABSTRACT FROM AUTHOR]

Composites of LiFePO4 and activated carbon (LFP-AC) were prepared by a ball milling method. Their morphologies were investigated by scanning electronic microscopy and energy dispersive spectroscopy. Hybrid supercapacitors were assembled using the LFP-AC composites as the positive electrode and Li4Ti5O12 as the negative electrode (LFP-AC/Li4Ti5O12). Effects of the positive electrode composition (ratio of LiFePO4 to AC) on the performance of LFP-AC/Li4Ti5O12 were investigated via constant current charge-discharge tests. The results demonstrated that the specific capacity and the specific power of the LFP-AC/Li4Ti5O12 hybrid supercapacitor significantly depend upon the content of LiFePO4 in the LFP-AC positive electrode. At 0.5 A g-1 charge-discharge current, the specific capacity of the LFP-AC/Li4Ti5O12 with 30 wt. % LiFePO4 and 70 wt. % AC in the positive electrode is 42% higher than that of AC/Li4Ti5O12, and the two supercapacitors have the same specific power. After 500 charge-discharge cycles at 1.0 A g-1, the specific capacity of the LFP-AC/Li4Ti5O12 with 80 wt. % LiFePO4 and 20 wt. % AC in the positive electrode is 53% higher than that of AC/Li4Ti5O12. The hybrid device stores electric energy via both the double-layer electrostatic adsorption and the intercalation/deintercalation of lithium ions. [ABSTRACT FROM AUTHOR]