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Potassium‐ion hybrid capacitors (PIHCs) overcome the limitations of potassium‐ion batteries (PIBs) and supercapacitors (SCs) and integrate the advantages of both, including high energy density, high power density, low cost, long cycle life, and stable electrochemical performance. However, the development of PIHCs is hindered by thermodynamic instability and kinetic hysteresis. Additionally, the dynamic mismatch between anode and cathode materials poses an urgent challenge. To this end, many research works related to material development have been dedicated to overcoming the drawbacks. In this review, the energy storage mechanism of PIHCs is briefly introduced. Moreover, the research progress and achievements of anode and cathode materials in recent years are reviewed, including carbon‐based materials, MXenes, transition metal materials, Prussian blue and its analogues. Finally, the challenges and prospects of PIHCs are proposed, together with guiding significant research directions in the future. [ABSTRACT FROM AUTHOR]

Thermal energy is abundantly available in our daily life and industrial production, and especially, low‐grade heat is often regarded as a byproduct. Collecting and utilizing this ignored energy by low‐cost and simple technologies may become a smart countermeasure to relieve the energy crisis. Here, a unique device has been demonstrated to achieve high value‐added conversion of low‐grade heat by introducing redox‐active organic alizarin (AZ) onto N‐doped hollow carbon nanofibers (N–HCNF) surface. As‐prepared N–HCNF/AZ can deliver a high specific capacitance of 514.3 F g−1 (at 1 A g−1) and an outstanding rate capability of 60.3% even at 50 A g−1. Meanwhile, the assembled symmetric proton capacitor can deliver a high energy density of 28.0 Wh kg−1 at 350.0 W kg−1 and a maximum power density of 35.0 kW kg−1 at 17.0 Wh kg−1. Significantly, the thermally chargeable proton capacitors can attain a surprisingly high Seebeck coefficient of 15.3 mV K–1 and a power factor of 6.02 µW g–1. Taking advantage of such high performance, a satisfying open‐circuit voltage of 481.0 mV with a temperature difference of 54 K is achieved. This research provides new insights into construction of high value‐added energy systems requiring high electrochemical performances. [ABSTRACT FROM AUTHOR]

Harvesting heat from the low‐grade heat (below 100 °C) into electricity has the signification to enhance the utilization of energy and lower carbon emissions by a simple device. Herein we demonstrate a thermally chargeable ammonium ion capacitor (TAIC) by employing graphene‐polyimide (rGO‐PI) synthesized through polycondensation of 1,4,5,8‐naphthalenetetracarboxylic dianhydride and ethylenediamine as cold electrode, N‐doped hollow carbon nanofibers as hot electrode to directly convert waste heat into electricity. Combining thermodiffusion effect of electrolyte with thermogalvanic effect of a redox couple (−C=O/−C−O−NH4+), as‐assembled TAIC can deliver a high output voltage of 624 mV, power density of 82 μW cm−2 and average Seebeck coefficient of 9.07 mV K−1 at temperature difference of 45 K. Meanwhile, with the introduction of polyacrylamide‐polyacrylic acid‐based gel electrolyte, the assembled flexible device can well serve in various bending states, and the power density can attain a satisfying value of 1.92 μW cm−2. This quasi‐solid‐state TAIC shows great potential as one promising candidate for high value‐added conversion from low‐grade heat into electricity as well as wearable applications. [ABSTRACT FROM AUTHOR]

Recently, developing matchable cathode materials of Zn ion hybrid capacitor still remains difficult owing to insufficient understanding of the charge storage behavior. However, most previous efforts are devoted to explain the effect of oxygen‐containing groups without paying attention to graphitic structure. Herein, the charge storage capability and electrochemical kinetics of reduce graphene oxide (rGO) nanosheets are optimized as a function of their surface properties. Beyond the contribution of oxygen‐containing groups, an extra contribution from the reversible adsorption/desorption of H+ on carbon atom of rGO sheets is confirmed. Electrochemical analysis and density functional theory calculations reveal that H+ induces disruption of π cloud in aromatic domain, accompanied by C sp2‐sp3 re‐hybridization and the distortion/restoration of graphitic structure. The optimal electrochemical performance with a specific capacitance of 245 F g‐1 at 0.5 A g‐1 with 53% retention at 20 A g‐1 is achieved for rGO thermally treated at 200 °C. As a proof‐of‐concept application, the 3D printed rGO electrode delivers a high areal capacitance of 1011 mF cm‐2 and an energy density of 266 μWh cm‐2. The study is believed to broaden the horizons of proton adsorption chemistry and shed light on the design of novel electrode materials. [ABSTRACT FROM AUTHOR]

Mesocrystals have received intense attention in the electrochemical energy storage field owing to their favourable electronic conductivity, high crystallinity and large specific surface area. However, a critical limitation to the wide applications of mesocrystals is the lack of a facile synthesis approach for high-performance mesocrystals. Here, we report a one-step self-assembly solvothermal method to prepare 3D hierarchical highly-ordered Nb3O7F nanowire cluster mesocrystals (denoted NOF-NCMs), of which the diameter of each nanowire is within 10 nm. Through kinetic analysis, NOF-NCMs can be confirmed to provide unique intercalation pseudocapacitance, enabling rapid charge transfer. When used as an anode material, the NOF-NCM electrode displays a high capacity of ∼356.7 mAh g−1 at 800 mA g−1, excellent rate performance and a long cycle life with ∼88.3% capacity retention after 3000 cycles. The improved electrochemical properties of NOF-NCMs are attributed to the unique highly-ordered nanowire cluster architectures. A lithium ion capacitor (LIC) is constructed by using well-prepared NOF-NCMs as an anode and commercial AC as a cathode. The NOF-NCMs//AC LIC can hold a maximum energy density of 74.5 W h kg−1 at 87.5 W kg−1, and has a long cycle lifespan with a 92.5% capacity retention after 3000 cycles and low self-discharge rate, demonstrating a bright candidate for applications in both high-energy and high-power electrochemical energy storage. [ABSTRACT FROM AUTHOR]

Lithium-ion capacitors (LICs) are gradually emerging as one of the most indispensable hybrid energy storage devices. However, it is one main challenge to evade the mismatch of electrochemical kinetics and specific capacity between cathode and anode in LICs. Herein, we have proposed an efficient strategy to prepare the nitrogen-doped hierarchical porous carbon spheres (NHPCS) as cathode, which is synthesized by a simple aerosol-spraying pyrolysis using the low-cost phenolic resin as carbon source without any other catalyst or hard template. The NHPCS exhibits porous nanospheres structure with an appropriate nitrogen doping level (3.65 at.%). Benefitting from the two-pronged strategy of N-doped feature and nanostructure engineering, NHPCS achieves a high specific capacity of 74 mAh g−1 at a current density of 0.1 A g−1 and remains 86.5% of initial capacity even being subjected to a high rate of 50-fold. Furthermore, a high-performance LIC has been developed by coupling NHPCS cathode and hard carbon anode, which delivers a maximum energy density of 151 Wh kg−1 and excellent cycle stability (96.3% capacity retention after 3000 cycles). Significantly, such designed porous carbon could not only be convenient for scalable production, but also be served for many other energy storage devices. We have presented a larger-scale spray pyrolysis strategy to prepare nitrogen-doped hierarchical porous carbon spheres (NHPCS). A high-stable lithium-ion capacitor has been constructed by coupling NHPCS cathode with hard carbon anode, which exhibits a maximum energy density of 151 Wh kg−1 and capacity retention of 96.3% over 3000 cycles, showing great potential for the next-generation energy storage application. [ABSTRACT FROM AUTHOR]

Sodium‐ion capacitors (SICs), designed to attain high energy density, rapid energy delivery, and long lifespan, have attracted much attention because of their comparable performance to lithium‐ion capacitors (LICs), alongside abundant sodium resources. Conventional SIC design is based on battery‐like anodes and capacitive cathodes, in which the battery‐like anode materials involve various reactions, such as insertion, alloying, and conversion reactions, and the capacitive cathode materials usually depend on activated carbon (AC). However, researchers have attempted to construct SICs based on battery‐like cathodes and capacitive anodes or a combination of both in recent years. In this Minireview, charge storage mechanisms and material design strategies for SICs are summarized, with a focus on the battery‐like anode materials from both inorganic and organic sources. Additionally, the challenges in the fabrication of SICs and future research directions are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Recently, lithium‐ion capacitors (LICs) combining the complementary characteristics of both lithium‐ion batteries (LIBs) and supercapacitors, have received exhaustive investigation to meet the increasing demands for clean energy. However, their commercial application has been limited by the mismatch of charge‐storage capacity and electrode kinetics between the capacitor‐type cathode and battery‐type anode. Thus, developing a novel high‐power insertion anode material is the key to realizing excellent energy and power densities for LICs. Here, 3D hierarchical Nb2O5 microspheres assembled by surface‐nitrogenated nanowires have been synthesized through a unique anti‐solvent precipitation‐assisted solvothermal route accompanied by a nitrogenization treatment, which can be successfully used for advanced LICs configuration. Owing to the high aspect ratio of ultrathin nanowires, unique pore structures caused by nitridation, improved electronic conductivity, and favorable kinetic stemming from pseudocapacitive behavior, the resultant nitrogenated Nb2O5 microspheres can deliver a high capacity of 205.3 mAh g−1 with remarkable rate capability and long lifespan. When constructed into a new LIC device with peanut‐shell derived carbon (PSC) cathode, an exceptionally high energy density of ∼83.5 Wh kg−1 and a high power density of 10 kW kg−1 with prominent cycling stability are realized. Significantly, the simultaneous manipulation of superstructure design and surface nitrogenization in novel anode material provides new opportunities to boost the energy and power densities for hybrid‐ion capacitors. [ABSTRACT FROM AUTHOR]

Heteroatom-doped nanostructured porous carbons have attracted intensive attention for electrical-double layer capacitors (EDLCs) because of their large surface area and surface functionalization. Here we use biowaste sepia ink as a sustainable source to synthesize nitrogen-doped highly porous carbon nanospheres by a simple molten salt-based activation strategy. The introduction of molten salt is not only beneficial for repairing the carbon conjugate network, but can also further improve the activation effect of porogen. The as-obtained carbon nanospheres (MA-NCS) displayed a large surface area of 1760 m2 g−1, optimized pore architecture, and high nitrogen content (8.6 wt %). With this design, the MA-NCS as EDLCs electrode exhibited a remarkable specific capacitance of 320 F g−1 at the current density of 0.5 A g−1 and high rate capability in 6 m KOH electrolyte. Furthermore, the assembled EDLCs demonstrated a high specific capacitance of 130 F g−1 at 0.5 A g−1 in an organic electrolyte (1 m TEABF4/AN), obtaining a maximum energy density of 28.2 Wh kg−1 at a power density of 625 W kg−1. This novel biowaste precursor-synthesis route presents great potential for facile large-scale production of high-performance porous carbons for green and long-term energy storage. [ABSTRACT FROM AUTHOR]

Flexible porous films are prepared from electrospun carbon nanofibers (CNFs) embedded with Co3O4 hollow nanoparticles (NPs) and are directly applied as self-supported electrodes for high-performance electrochemical capacitors. Uniform Co3O4 hollow NPs are well dispersed and/or embedded into each CNF with desirable electrical conductivity. These Co3O4-CNFs intercross each other and form 3D hierarchical porous hybrid films. Benefiting from intriguing structural features, the unique binder-free Co3O4 hollow NPs/CNF hybrid film electrodes exhibit high specific capacitance (SC), excellent rate capability and cycling stability. As an example, the flexible hybrid film with loading of 35.9 wt% Co3O4 delivers a SC of 556 F g−1 at a current density of 1 A g−1, and 403 F g−1 even at a very high current density of 12 A g−1. Remarkably, almost no decay in SC is found after continuous charge/discharge cycling for 2000 cycles at 4 A g−1. This exceptional electrochemical performance makes such novel self-supported Co3O4-CNFs hybrid films attractive for high-performance electrochemical capacitors. [ABSTRACT FROM AUTHOR]

Nanostructured CoNi-Al layered triple hydroxides (CoNi-Al LTHs) have been successfully synthesized by a facile hydrothermal method using glycine as chelating agent. The samples were characterized by X-ray diffraction, thermogravimetry, Fourier transform infrared spectroscopy and scanning electron microscopy. The morphologies of CoNi-Al LTHs varied with the Co content and its effect on the electrochemical behavior was studied by cyclic voltammetry and galvanostatic charge-discharge techniques. Electrochemical data demonstrated that the CoNi-Al LTHs with Co/Ni molar ratio of 3:2 owned the best performance and delivered a maximum specific capacitance of 1,375 F g at a current density of 0.5 A g and a good high-rate capability. The capacitance retained 93.3% of the initial value after 1,000 continuous charge-discharge cycles at a current density of 2 A g. [ABSTRACT FROM AUTHOR]

Lithium‐ion capacitors (LICs) are emerging as one of the most advanced energy storage devices by combining the virtues of both supercapacitor and lithium‐ion battery. The key point of constructing high‐performance LICs is to balance the electrochemical kinetics and capacity mismatch between battery‐type anode and capacitive‐type cathode materials. Herein, a strategy is presented for simultaneous manipulation of a MoS2/N‐doped carbon microspheres anode and hierarchical porous carbon cathode by using polyimide precursor. Owing to the fast lithium diffusion rate, high pseudocapacitive behavior, and expanding the interlayer of the MoS2 composite network architecture, the material can achieve excellent rate capacity and cyclic stability. Hierarchical porous carbon has an ultrahigh specific surface area and superior capacitive behavior. A high‐performance LIC is successfully constructed by using the superior anode and cathode materials. The device can deliver a maximum energy density of 120 Wh kg−1 and keep the capacity retention of 85.5% after 4000 cycles, revealing the competition in advanced energy storage devices. Accordingly, the simultaneous manipulation of metal sulfide and hierarchical porous carbon by the same precursor can be used toward fabricating other ideal electrode structures for energy storage. [ABSTRACT FROM AUTHOR]

The 2D carbon sheets have great potential for the construction of compact electrodes with high volumetric performance for electrical double‐layer capacitors (EDLCs), by virtue of their excellent electrical conductivity, high exposed surface area, free of interpores, and unimpeded ion‐diffusion channels. However, 2D nanosheets restack and aggregate during the preparation processes of electrodes, reducing available surface area, and limiting transport of ions. Herein, a facile and scalable method is presented to prepare highly porous crumple carbon balls (PCCBs) assembled by 2D carbon nanosheets. Such a unique nanostructure endows the PCCB electrode with large electrolyte‐accessible surface area and short ion‐diffusion pathways even when compressed at 40 MPa. Electrochemical evaluations in 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIMBF4) electrolyte indicate that the compressed PCCB electrodes still show superior gravimetric (103 F g−1) and volumetric capacitances (127 F cm−3) at 1 A g−1. The highest volumetric energy density of symmetrical EDLC based on compressed PCCB‐based electrode is 53.9 Wh L−1. This work provides a new direction for the development of high volumetric energy density carbon‐based EDLCs. [ABSTRACT FROM AUTHOR]

The Fe 7 Se 8 @NC nanorods were prepared via an in-situ self-polymerization and carbonization-selenization strategy. With the optimization of voltage range and electrolyte parameters, the Fe 7 Se 8 @NC electrode delivers desirable rate capability and long-term cyclability. Coupled with activated carbon (AC), the assembled sodium-ion capacitor (Fe 7 Se 8 @NC//AC) delivers a maximum energy density of 81 Wh kg−1 and remarkable capacity retention of 94.4% after 5000 cycles. [Display omitted] With the associated advantages of low costs and abundant resources, sodium-ion capacitors (SICs) present a suitable means for large-scale energy storage. However, their practical application is still significantly limited by the sluggish electrochemical reaction kinetics of battery-type anodes. Herein, the nitrogen-doped carbon-encapsulated Fe 7 Se 8 nanorods (Fe 7 Se 8 @NC) with a core–shell structure were prepared via an in-situ self-polymerization and carbonization–selenization approach, which improves ion transport and maintains the structural stability of the nanorods. The designed Fe 7 Se 8 @NC nanorods exhibit desirable rate capability with a capacity of 290.7 mAh/g at 10 A/g and long-term cyclability with 84.6 % retention over 6000 cycles at 5 A/g. Moreover, research has shown that the diffusion dynamics of Na+ is improved in ether-based electrolytes and that the irreversible reactions at low voltages can be inhibited by a high discharge cut-off voltage. Furthermore, we demonstrated the specific sodium storage mechanism and excellent electrochemical reversibility of the Fe 7 Se 8 @NC electrode through in-situ and ex-situ characterization techniques. As expected, the assembled SICs with the Fe 7 Se 8 @NC anode and active carbon cathode deliver prominent energy/power densities and an ultra-long cycle life over 5000 cycles, shedding new light on the design of transition metal dichalcogenides as anode materials for advanced energy storage systems. [ABSTRACT FROM AUTHOR]

Developing lithium ion capacitors (LICs) with high energy density is still challenging, due to the kinetic mismatch between the capacitor-type cathode and the battery-type anode. In addition, metal-free LICs are preferred over high-cost and unsustainable metal-containing electrode materials. Exploring appropriate metal-free cathode and anode materials with high capacity and excellent rate performance is one of the keys to attain such goal. Herein, nanoarchitectured graphene-based LICs are successfully constructed by using 2D polydopamine-graphene heterostructured anode and porous graphene cathode. The 2D nature of polydopamine-graphene facilitate the transport of electrolyte ions while graphene promotes electron transfer. The high specific surface area of the porous graphene endows ions with accessibility and fast transport. The metal-free LIC device achieves a high energy density (135.6 Wh kg−1 at 210.4 W kg−1), high power density (21.0 kW kg−1 at 78.9 Wh kg−1), high low-temperature performance (76.4 Wh kg−1 at −20 °C), and reasonably long cycling life. This work provides an effective strategy to design metal-free LIC with high performance at wide temperature range. Image 1 [ABSTRACT FROM AUTHOR]

The defect-rich and N -doped anode was prepared from the renewable sepia by a simple pyrolysis process. The electrochemical kinetic analyses and density functional theory calculations have confirmed its prominent pseudocapacitive behaviors and excellent Li+ storage capability. A high-energy lithium-ion capacitor has been constructed by this low-cost hard carbon anode, which shows great potential for next-generation energy storage device. Lithium-ion capacitors (LICs) are regarded as the most potential devices in the energy storage systems. Unfortunately, the mismatched in the intrinsic kinetics and specific capacities between anode and cathode lead to a depressed electrochemical performance. Thus, designing an advanced electrode material that combines high performance with low-cost is one of the main challenges for LICs, especially in a sustainable anode material until now. Here, a high-energy LIC has been successfully developed using the defect-rich and N -doped hard carbon (DNC) as anode, which is prepared through the carbonization process of the low-cost biowaste sepia without additional template or catalyst. The DNC shows nanospherical structure with a diameter of about 100 nm. Owing to the two-pronged strategy of N -doping and defect engineering, it delivers a high specific capacity (580.3 mAh g−1 at 0.05 A g−1), excellent rate capability, and long cycle stability (1000 cycles). The electrochemical kinetic analysis and density functional theory (DFT) calculations have confirmed its prominent pseudocapacitive behaviors and excellent Li+ storage capability. As expected, the as-fabricated LIC delivers a remarkable energy density (101.7 Wh kg−1), an outstanding rate capability (56.3 Wh kg−1 at 12.5 kW kg−1), and a superior cycle lifespan (3000 cycles), demonstrating the tremendous potential for the next-generation energy storage systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Manipulating anions to obtain the novel LiOTf-based LHE with excellent properties. • LHE enables hybrid capacitor with high voltage and good rate capability. • Hybrid capacitor realized long cycling by LiOTf derived aqueous CEI. • EQCM-D, XPS and FIB-SEM results reveal the generation and composition of CEI. Aqueous electrochemical energy storages have multiple advantages especially safety performance in the energy storage process. The high concentration aqueous electrolytes with a wide electrochemical stable voltage window (ESW) solves the key problems of aqueous electrochemical energy storages. It effectively breaks the limitation of H 2 O molecule decomposition to realize aqueous electrochemical energy storage with high operating voltage. However, the slow ion transport and high cost limit their application in power-type storages. Here, the lacked H-bond aqueous electrolyte (LHE) is proposed by investigating the structures and properties of aqueous electrolytes with various chaotropic anions. The LHE achieves high conductivity, low viscosity, and low cost while ensuring a wide ESW. These excellent properties originate from the OTf− effect on the solvation structure of cations and the number of H-bonds. An aqueous Li-ion hybrid capacitor (LHC) with the LHE exhibits high operating voltage of 2.5 V and high ESW utilization of 92.6 %. The aqueous cathode electrolyte interphase formed by anions on the cathode surface also achieved a long cycle life for the LHC. It has guided the development of novel electrolytes for electrochemical energy storage. [ABSTRACT FROM AUTHOR]

Lithium ion capacitors combine the complementary advantageous characteristics of batteries and supercapacitors are expected to deliver both high energy and high power density. However, this technology suffers from the kinetics imbalance between battery electrode and capacitive electrode. Here, two dimensional T -Nb 2 O 5 /N-doped carbon nanosheets with a well-continuous ionic/electronic conducting network demonstrate superior rate capability of 142.3 mA h g−1 at 20 C (1 C = 200 mA g−1). A majority of charge storage in the T -Nb 2 O 5 /N-doped carbon nanosheets was proved to be intercalation pseudocapacitive processes by kinetic analysis, enabling fast charge storage performance. A lithium ion capacitor is based upon these T -Nb 2 O 5 /N-doped carbon nanosheets was successfully fabricated, demonstrating high energy density (70.3 W h kg−1) and high power density (16,014 W kg−1). Unlabelled Image • A well-continuous ionic/electronic conducting network of Nb 2 O 5 /C was rational design and constructed. • The T - Nb 2 O 5 /NC NSs electrode exhibits remarkable rate capability and long cycle life. • T -Nb 2 O 5 /NC NSs//PSC lithium ion capacitor demonstrates high energy density, high power density and long cycle life. [ABSTRACT FROM AUTHOR]

The synthesis of highly nitrogen-doped hierarchical carbon spheres (NPCS) is reported. The NPCS with pomegranate-like nanostructure were prepared by the CaCO 3 spheres template-induced self-activation route with dopamine as the carbon precursor. The template-induced self-activation mechanism was carefully investigated by controlling experiment conditions and thermogravimetric analyses combined with mass spectrometry. Under the optimized conditions, the as-prepared NPCS demonstrate large specific area (up to 1984 m 2  g −1 ) and high level of nitrogen (N, 7.57%) doping. Electrochemical evaluations indicate that the energy density of NPCS-based EDLC devices can reach 6.2 and 14.4 Wh kg −1 in 6 M KOH electrolyte and aqueous concentrated electrolyte (5 M LiTFSI), respectively. This work provides a novel approach for preparing nanoporous carbon materials with hierarchical porosity and well-defined nanostructure. [ABSTRACT FROM AUTHOR]

The manufacturing processes of electrodes have a prominent influence on the cost and performance of lithium-ion capacitors (LICs), which are limited by the conventional wet-coated method due to the usage of solvent. Herein, the solvent-free Li 4 Ti 5 O 12 (LTO) electrodes are prepared with electrostatic spraying deposition using for LICs. Owing to the solvent being avoided during the manufacturing, the dry-sprayed electrode exhibits a higher porosity (∼40%) than that of the wet-coated electrode (∼30%), together with a larger electrochemically active surface area. The optimized microstructure improves electrolyte infiltration and offers effective Li-ion transport paths, which reduces the electrochemical polarization and boosts the specific capacity of the dry-sprayed electrode. When the current density increases from 0.5 C to 10 C, the reversible capacity retention of the dry-sprayed electrode is 74%, which is higher than that of the wet-coated electrode (56%). In addition, the powder resistivity of the dry-sprayed electrode decreases sharply by introducing two-dimension (2D) graphene nanoplate (GN) as the conductive agent, thus side effects have been effectively suppressed during the spraying process. As a result, the assembled LICs using the dry-sprayed LTO electrodes show superior energy density and excellent cycling performance, demonstrating this novel fabrication method has practical application prospects. [Display omitted] • Solvent-free Li 4 Ti 5 O 12 electrodes are prepared by electrostatic spraying. • The differences between dry-sprayed and wet-coated electrodes are explored. • The optimization of electrode microstructure helps properties improve. • Adopting graphene nanoplates as conductive agents perfects spraying results. • Li-ion capacitors with solvent-free electrodes exhibit better performance. [ABSTRACT FROM AUTHOR]

To enhance kinetics of lithium insertion/extraction of anode materials for hybrid lithium-ion capacitors (hybrid LICs), we develop a new applicable strategy toward the synthesis of trivalent Ti self-doped Li 4 Ti 5 O 12 nanoparticles. Starting with Ti 2 O 3 , we show that subsequent solid state reaction with Li 2 CO 3 leads to the formation of trivalent Ti self-doped Li 4 Ti 5 O 12 . The presence of trivalent Ti gives rise to high electric conductivity and the nanostructure reduces the transport path lengths of lithium-ions and electrons, permitting fast kinetics for both transported lithium-ions and electrons, thus enabling high-power performance. A high performance hybrid LIC is fabricated by using Ti 3 + self-doped Li 4 Ti 5 O 12 as an insertion-type anode and activated carbon derived from outer peanut shell as cathode, which delivers high energy density (67 Wh kg − 1 ), high power density (8000 W kg − 1 ). Additionally, the device still retains about 79% of its original capacity even after 5000 cycles at 0.5 A g − 1 . [ABSTRACT FROM AUTHOR]

Abstract: We developed a sacrificial template strategy to synthesize short NiO nanotubes (S-NiO NTs) with mesopores in sidewalls by using short carbon NTs as template for electrochemical capacitors. Further physical characterizations exhibited that as-synthesized S-NiO NTs owned a specific surface area of 150m2 g−1 and hierarchical (meso- and macro-) porosity. Electrochemical data presented that such NTs delivered a specific capacitance of 903Fg−1 at 1Ag−1, much larger than those of long NiO NTs and NiO nanoparticles. The capacity retention of ca. 88%, when the current density increased from 1 to 4Ag−1, indicated high rate capability of the unique S-NiO NTs electrode. Furthermore, a capacitance degradation of ca. 6% after 2000 charge–discharge cycles at 4Ag−1 demonstrated their desirable electrochemical stability. The short tubular and hierarchical porous feature of the S-NiO NTs resulted in the high electrochemical utilization for energy storage even at high rates. [Copyright &y& Elsevier]

Abstract: In the work, multi-walled carbon nanotubes (MWCNTs) were coated uniformly onto the cotton fibers to make porous conductive cotton textile, where MWCNTs formed an electrically conductive interconnecting network. Then, a flexible, lightweight, cheap and porous composite was synthesized for electrochemical capacitors (ECs) by dispersed pseudocapacitive cobalt hydroxide well onto the conductive cotton textile sheet. Electrochemical results show that the unique flexible and porous composite owns the ability to deliver large area specific capacitance of 11.22Fcm−2 and good electrochemical stability of 4% capacity loss after 2000 cycles at high rates. Moreover, the extremely simple design and fabrication process we proposed here provide a universal and efficient approach to large-scale production of flexible, lightweight, low-cost and porous electrode for ECs application. [Copyright &y& Elsevier]

Abstract: A novel and facile non-covalent process was applied to sulfonate multiwalled carbon nanotubes (MWCNTs) with a high –SO3H loading carbonaceous (C-SO3H). Then the sulfonated multi-walled carbon nanotubes/polypyrrole nanocomposite (MWCNTs/C-SO3H/PPy) was synthesized by the in situ chemical polymerization of pyrrole on the non-covalent sulfonated MWCNTs (MWCNTs/C-SO3H) using ammonium persulfate as oxidant at low-temperature. Fourier transform infrared (FT-IR) spectra confirm the modification of MWCNTs and an existence of interaction between the –SO3H group of the modified MWCNTs and the N–H group of PPy. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), FT-IR and ultraviolet–visible (UV–vis) spectra show that uniform PPy layer coated on the sidewall of MWCNTs/C-SO3H. The electrochemical properties of the MWCNTs/C-SO3H/PPy composite were studied by cyclic voltammetry and galvanostatic charge/discharge test. The composite possesses good rate response and stable specific capacitance, the specific capacitance loss is only 3% even after the 1000 cycles. [Copyright &y& Elsevier]

Abstract: In this work, poly(sodium-4-styrene sulfonate) (PSS)-functionalized multi-walled carbon nanotubes (FMWCNTs) were first synthesized via a polymer-assisted technique. Then, Ru0.58In0.42O y ⋅nH2O nanoparticles (NPs) were mono-dispersed onto the FMWCNTs surfaces under mild hydrothermal condition. Here, PSS with negative charge serves as a bifunctional molecule both for solubilizing and dispersing MWCNTs into aqueous solution and for tethering Ru3+ and In3+ to facilitate the good dispersion of Ru1− x In x O y ⋅nH2O NPs onto their surfaces. The good dispersion of Ru0.58In0.42O y ⋅nH2O NPs onto FMWCNTs makes OH− ions and electrons easily contact these NPs with abundant electroactive sites, which results in a large specific capacitance (SC) of 319Fg−1 for the naocomposites. Moreover, a symmetric electrochemical capacitor (EC) is constructed by using the nanocomposites as electrodes and delivers large specific energy density of 18.1Whkg−1, desirable power property of 1302Wkg−1, high electrochemical reversibility and good SC retention of 84.7%. [ABSTRACT FROM AUTHOR]

Abstract: An efficient interface-hydrothermal approach is developed to synthesize Sn3S4/graphene sheet composites (SSGSCs), where the graphene sheets (GSs) are separated by fine Sn3S4 nanoparticles (NPs) well-dispersed onto their surfaces. The SSGSCs are investigated as electroactive materials for electrochemical capacitors (ECs) application. Due to the positive synergistic effect of GSs and Sn3S4 NPs, the unique SSGSCs electrode owns the ability to deliver large specific capacitance and good electrochemical stability at high rates. Moreover, the method we proposed here provides a universal and simple approach to synthesize other metal sulfides/GSs composites for ECs and even for Li-ion battery applications. [ABSTRACT FROM AUTHOR]

Abstract: A loose whisker-like Co(OH)2 was synthesized by means of polyethylene glycol 4000 as soft template under ultrasonic condition, and investigated as an active electrode material for electrochemical capacitors. The composition and microstructure of the as-prepared Co(OH)2 were investigated by X-ray diffraction spectroscopy and transmission electron microscopy. The formation mechanism of the whisker-like Co(OH)2 was attentively proposed based on Fourier transform infrared spectroscopy analysis. Electrochemical studies revealed that the whisker-like Co(OH)2 delivered a specific capacitance of 325F/g at a current density of 20mA/cm2 (ca. 1.3A/g) and even 279F/g at 80mA/cm2 (ca. 5.3A/g) due to its special nanostructure, indicating its fast electrochemical response property. A capacitance attenuation of ca. 7% over 1000 cycles meant the good cyclic stability of the whisker-like Co(OH)2 for electrochemical capacitors application. [Copyright &y& Elsevier]

Abstract: A noncovalent method was used to functionalize multiwalled carbon nanotubes with poly (sodium 4-styrene sulfonate). And then, the core–shell poly (3,4-ethylenedioxythiophene)/functionalized multiwalled carbon nanotubes (PEDOT/PSS-CNTs) nanocomposite was successfully realized via in situ polymerization under the hydrothermal condition. In the process, PSS served for not only solubilizing and dispersing CNTs well into an aqueous solution, but also tethering EDOT monomer onto the surface of CNTs to facilitate the formation of a uniform PEDOT coating. Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) were used to characterize the resultant PEDOT/PSS-CNTs. In addition, the PEDOT/PSS-CNTs nanocomposite (50wt.% PEDOT) had a specific capacitance (SC) of 198.2Fg−1 at a current density of 0.5Ag−1 and a capacitance degradation of 26.9% after 2000 cycles, much better than those of pristine PEDOT and PEDOT/CNTs (50wt.% PEDOT). The enhanced electrochemical performance of the PEDOT/PSS-CNTs nanocomposite (50wt.% PEDOT) should be attributed to the high uniform system of the nanocomposite, resulting in the large surface easily contacted by abundant electrolyte ions through the three-dimensional conducting matrix. [Copyright &y& Elsevier]

• A copper hyperaccumulator is used to synthesize nanoporous carbon. • The structure of nanoporous carbon was rationally optimized. • Nanoporous carbon anode shows a capacitance-dominated dynamic process. • High specific surface area carbon cathode reveals a high specific capacity. • A high energy Li-ion capacitors with dual carbon configuration has been assembled. Biomass-based porous carbons as electrode materials in asymmetric Li-ion capacitors (LICs) have shown broad prospect application. In this work, one kind of copper hyperaccumulator-elsholtzia splendens was selected as biomass source to synthesize micro-/nanoporous carbons to be used as both anode and cathodefor LICs due to the need of waste disposal. On the basis of separate charge storage mechanisms of anode and cathode in this system, corresponding strategies were adopted to rationally optimize the microstructure of micro-/nanoporous carbons to promote their electrochemical performance. Electrochemical tests showed that hierarchical porous carbon microsphere (PECS) anode exhibited an excellent rate capability (215.6 mA h g−1 at 2 A g-1) and a long lifespan (87.1% capacity retention over 1000 cycles). Carbon cathode with an ultrahigh specific surface area of 2819 m2 g-1 revealed a high specific capacity of 90.9 mA h g−1 at 5 A g-1. Benefiting from the high rate capability of anode and the high specific capacity of cathode, the as-assembled LIC delivered a high energy density of 129.4 W h kg−1 and 51.9 W h kg−1 at a power density of 205.5 W kg−1 and 10.3 kW kg−1. [ABSTRACT FROM AUTHOR]

[Display omitted] • New hybrid system adopts lithium/sodium mixed organic solvent as electrolyte. • The potential window of LTO MS L/SIB system is broadened. • A four-step charge storage mechanism is proposed. • New hybrid supercapacitors (LTO MS//PSC L/SIC) show excellent electrochemical properties. Reportedly, Li 4 Ti 5 O 12 could provide the novel characteristics of both Li+ insertion and Na+ insertion. In this work, we firstly take advantage of this unique feature and use lithium/sodium mixed organic solvent as electrolyte for evaluating the electrochemical performance of as-synthesized Li 4 Ti 5 O 12 nano-microspheres (LTO MS). As a result, the potential window of LTO MS is broadened, leading to full utilization of Li 4 Ti 5 O 12. In addition, the difference between insertion potentials of Li+ and Na+ inserting into LTO MS is applied to reasonably intercept the potential windows of LTO MS, ensuring its remarkable cycling stability and high rate property. Therefore, LTO MS using lithium/sodium mixed electrolyte (LTO MS-L/SIB system) can provide a broadened potential window of 0.4–2.5 V, leading to a high specific capacity without sacrificing rate performance and cycling stability. We also systemically analyze the charge storage mechanism of LTO MS-L/SIB by ex-situ XRD technologies. For the first time, the lithium-sodium hybrid ion capacitor (LTO MS//PSC L/SIC) is constructed with LTO MS as anode, peanut shell derived carbon (PSC) as cathode, and lithium-sodium mixed organic solvent as electrolyte. Compared with the as-constructed lithium ion capacitors (LTO MS//PSC LIC) and sodium ion capacitors (LTO MS//PSC SIC), LTO MS//PSC L/SIC device provides the highest gravimetric energy density of ~65.3 Wh kg−1, a remarkable cycling stability, and an ultra-low self-discharge rate. [ABSTRACT FROM AUTHOR]

Abstract: Co-functionalized titanate nanotubes (Co-Ti-NTs) were successfully synthesized by means of an ion-exchange reaction. In contrast to the pristine titanate nanotubes (Ti-NTs), Co-Ti-NTs retained rich porous channels and owned even larger specific surface area and better electronic conductivity, which rendered electrons and OH− ions easily contact the Co species uniformly distributed on their surfaces for energy storage at high rates. The Co-Ti-NTs delivered a specific capacitance (SC) of 124Fg−1 at 0.4Ag−1, and a SC degradation of ca. 7% after 1500 continuous cycling at 3Ag−1, indicating that the Co-Ti-NTs were good candidates and/or even good supports for other electroactive materials for supercapacitors application. [Copyright &y& Elsevier]