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Metal‐covalent organic frameworks (MCOF) as a bridge between covalent organic framework (COF) and metal organic framework (MOF) possess the characteristics of open metal sites, structure stability, crystallinity, tunability as well as porosity, but still in its infancy. In this work, a covalent organic framework DT‐COF with a keto‐enamine structure synthesized from the condensation of 3,3′‐dihydroxybiphenyl diamine (DHBD) and triformylphloroglucinol (TFP) was coordinated with Cu2+ by a simple post‐modification method to a obtain a copper‐coordinated metal‐covalent organic framework of Cu‐DT COF. The isomerization from a keto‐enamine structure of DT‐COF to a enol‐imine structure of Cu‐DT COF is induced due to the coordination interaction of Cu2+. The structure change of Cu‐DT COF induces the change of the electron distribution in the Cu‐DT COF, which greatly promotes the activation and deep Li‐storage behavior of the COF skeleton. As anode material for lithium‐ion batteries (LIBs), Cu‐DT COF exhibits greatly improved electrochemical performance, retaining the specific capacities of 760 mAh g−1 after 200 cycles and 505 mAh g−1 after 500 cycles at a current density of 0.5 A g−1. The preliminary lithium storage mechanism studies indicate that Cu2+ is also involved in the lithium storage process. A possible mechanism for Cu‐DT COF was proposed on the basis of FT‐IR, XPS, EPR characterization and electrochemical analysis. This work enlightens a novel strategy to improve the energy storage performance of COF and promotes the application of COF and MCOF in LIBs. [ABSTRACT FROM AUTHOR]

Lithium‐ion batteries (LIBs) have been widely used as a new energy storage system with high energy density and long cycle life. However, the solid electrolyte interface (SEI) formed on the surface of anode consumes excess active lithium during the initial cycle, resulting in an initial irreversible capacity loss (ICL) and reducing the overall electrochemical performance. To solve the critical issue, pre‐lithiation technology has been accepted as one of the most promising strategies. Due to the pre‐lithiated treatment provides additional active lithium to compensate for the ICL and effectively improves initial Coulombic efficiency (ICE), leading to raising the working voltage, increasing the Li+ concentration, as well as improving the energy density and cycle stability of LIBs. In this overview, the causes of ICL in LIBs are analyzed from different perspectives, and various pre‐lithiation strategies are systematically classified and summarized. Finally, some current problems and development prospects in this field are summarized, with prospects for realizing industrialized technologies. [ABSTRACT FROM AUTHOR]

Simultaneously achieving high energy density and high‐power density in energy storage systems is a crucial direction for developing next‐generation energy storage technologies. The high capacity and rapid kinetic performance of rechargeable proton batteries provide an ideal solution for overcoming energy limitation of capacitors and power constraints of traditional metal‐ion batteries. Research efforts primarily concentrated on electrode materials design, understanding the charge storage mechanisms, and exploring the failure mechanisms. While there has been relatively less emphasis on the modifications to electrolytes and electrode‐electrolyte interfaces to enhance overall performance. Summarizing and sorting relevant work is crucial in providing direction and suggestions for future research endeavors. Herein, to improve energy density, power density, and cycle stability of proton batteries, a series of recently published studies on electrolyte and electrode‐electrolyte interfaces are discussed and reviewed. Furthermore, challenges and future directions pertaining to the electrolytes of proton batteries have been identified, offering insights to facilitate the development of proton battery technology. [ABSTRACT FROM AUTHOR]

Highlights: Solvation engineering toward dual-salt electrolyte by fluorosurfactant additive is proposed, which implements the stable interface of electrode/electrolyte coupled with fast ion thermodiffusion, improving the durability and capability of lithium-ion thermoelectrochemical cell. By combining the optimized electrolyte with functional electrodes, as-constructed device exhibits high Seebeck coefficient and energy density based on hybrid mechanisms, which can be extended as self-power supply for smart electronics. Lithium-ion thermoelectrochemical cell (LTEC), featuring simultaneous energy conversion and storage, has emerged as promising candidate for low-grade heat harvesting. However, relatively poor thermosensitivity and heat-to-current behavior limit the application of LTECs using LiPF6 electrolyte. Introducing additives into bulk electrolyte is a reasonable strategy to solve such problem by modifying the solvation structure of electrolyte ions. In this work, we develop a dual-salt electrolyte with fluorosurfactant (FS) additive to achieve high thermopower and durability of LTECs during the conversion of low-grade heat into electricity. The addition of FS induces a unique Li+ solvation with the aggregated double anions through a crowded electrolyte environment, resulting in an enhanced mobility kinetics of Li+ as well as boosted thermoelectrochemical performances. By coupling optimized electrolyte with graphite electrode, a high thermopower of 13.8 mV K−1 and a normalized output power density of 3.99 mW m–2 K–2 as well as an outstanding output energy density of 607.96 J m−2 can be obtained. These results demonstrate that the optimization of electrolyte by regulating solvation structure will inject new vitality into the construction of thermoelectrochemical devices with attractive properties. [ABSTRACT FROM AUTHOR]

Ionic and electronic transport in electrodes is crucial for electrochemical energy storage technology. To optimize the transport pathway of ions and electrons, electrode materials are minimized to nanometer-sized dimensions, leading to problems of volumetric performance, stability, cost, and pollution. Here we find that a bulk hexagonal molybdenum oxide with unconventional ion channels can store large amounts of protons at a high rate even if its particle size is tens of micrometers. The diffusion-free proton transport kinetics based on hydrogen bonding topochemistry is demonstrated in hexagonal molybdenum oxide whose proton conductivity is several orders of magnitude higher than traditional orthorhombic molybdenum oxide. In situ X-ray diffraction and theoretical calculation reveal that the structural self-optimization in the first discharge effectively promotes the reversible intercalation/de-intercalation of subsequent protons. The open crystal structure, suitable proton channels, and negligible volume strain enable rapid and stable proton transport and storage, resulting in extremely high volumetric capacitance (~1750 F cm–3), excellent rate performance, and ultralong cycle life (>10,000 cycles). The discovery of unconventional materials and mechanisms that enable proton storage of micrometer-sized particles in seconds boosts the development of fast-charging energy storage systems and high-power practical applications. Nanostructured electrode materials pose several challenges, including poor volumetric performance, severe side reactions, high costs, and complexity. Here, the authors develop a micrometer-sized bulk hexagonal molybdenum oxide with unconventional charge storage mechanism for fast and stable proton storage. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries (LIBs) are widely used in the mobile electronics, power, energy storage and other fields due to their excellent electrochemical performance, but their limited service life has resulted in a large number of spent LIBs being discarded. Due to the advantages of high recovery efficiency and mild reaction conditions, the combined pyro-hydrometallurgical process for recovering valuable metal elements from spent LIBs is emerging in line with the principles of green chemistry and has potential for large-scale industrial applications. Here we review current developments in the combined recovery process, aiming to figure out the challenges and future directions for the combined process. In detail, thermal pretreatment methods for collecting the cathode material from spent LIBs, the combined recovery process for treating the cathode material, and the subsequent separation and extraction process are summarized. Furthermore, the practical application of combined recycling schemes is demonstrated. Finally, the development and challenges of the combined process in recycling spent LIBs are revealed. Achieving pollution-free emissions and high-value utilization of spent LIB resources with low-cost treatment are future directions for the combined process. [ABSTRACT FROM AUTHOR]

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]

Proton batteries have been considered as an innovative energy storage technology owing to their high safety and cost‐effectiveness. However, the development of fast‐charging proton batteries with high energy/power density is greatly limited by feasible material selection. Here, the pre‐protonated vanadium hexacyanoferrate (H‐VHCF) is developed as a proton cathode material to alleviate the capacity loss of proton‐free electrode materials during electrochemical tests. The pre‐protonation process realizes fast and long‐distance transport of protons by shortening diffusion path and reducing migration barriers. Benefitting from the enhanced hydrogen bonding network combined with dual redox reactions of V and Fe in protonated H‐VHCF cathode, a high energy density of 74 Wh kg−1 at 1.1 kW kg−1, and a maximum power density of 54 kW kg−1 at 65 Wh kg−1 is achieved for the asymmetric proton batteries coupling with MoO3/MXene anode. Proton transport and double oxidation‐reduction center are verified by theoretical calculations and ex situ experimental measurements. Considering the anti‐freezing availability of proton batteries, 82.5% of its initial capacity is maintained after 10000 cycles under −40 °C at 0.5 A g−1. As a proof‐of‐concept, flexible device fabricated by optimized electrodes and hydrogel electrolytes can power up a light‐emitting diode even under a bent state. [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]

Siloxane‐based molecular material, by virtue of its unique chemical structure, thermal and electrochemical properties, has triggered tremendous research interest and sparked a revolution for energy storage in the past years. Siloxanes and their analogues are generally demonstrated to be more environmentally friendly, durable, and safer when employed to reconstruct the nano‐micro surface structure of electrodes, separators, and their interfaces with electrolytes. To better understand the recent and comprehensive achievement of siloxane‐based materials in energy storage, a systematic summary is necessary to provide important clues, aiming at achieving better electrochemical properties. In this Minireview, siloxane materials are presented comprehensively and systematically in terms of molecule design, functionality, and unique superiority for lithium‐ion batteries and supercapacitors. The challenges, perspectives, and future directions of siloxane‐based organosilicon materials are put forward for higher performance and wider application in electrochemical energy storage devices. [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]

Metal–oxygen batteries have been growing rapidly as an energy storage technology in light of their high specific energy density. However, waste metal–oxygen batteries will raise many environmental issues; therefore, the recycling and reusing of the spent metal–oxygen batteries has attracted great attention. Herein, we report the 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) as a redox mediator for manganese–oxygen battery (MOB). Trace amounts of PTIO result in the discharge capacity of MOB increase to 2588 mAh g−1 and enhance the formation of manganese dioxide (MnO2) with toroidal appearance and high crystallinity on the cathode. After being used, the dismantled MnO2/carbon nanotube (CNT) cathode can be reused as an electrode for supercapacitor via simple calcining at mild temperature. The recycled free-standing MnO2/CNT electrode demonstrates an exceptional specific capacitance (253.86 F g−1) at a current density of 0.5 A g−1 in a 0.5 M Na2SO4 electrolyte. Moreover, we prepare an asymmetric supercapacitor fabricated with the recycled MnO2/CNT electrode and activated carbon (AC), which exhibits excellent energy density (32.00 Wh kg−1 at 413.70 W kg−1) with 78.26% retention over 6000 cycles. This work provides a promising strategy to derive high-quality and high-value MnO2/CNT electrode materials from the spent MOBs. It's the 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) as a redox mediator for manganese-oxygen battery (MOB). The recycled manganese dioxide (MnO2)/carbon nanotube (CNT) cathode can be reused as an electrode for supercapacitor via simple calcining at mild temperature. The recycled MnO2/CNT electrode shows the toroidal appearance and high crystallinity. Furthermore, the asymmetric supercapacitor fabricated with the MnO2/CNT free-standing electrode displays high specific capacitance, superior energy density, and good cyclic ability. [ABSTRACT FROM AUTHOR]

Electrochemical proton storage provides high energy, fast kinetics, safety, and environmental friendliness for grid‐scale energy storage. However, the development of pseudocapacitive proton supercapacitors with fast chargeability and high stability is still challenging because of the unclear electrochemical reaction mechanism and unsuitable construction strategy. Here it is shown that a multi‐metallic Prussian blue analog—Cu0.82Co0.18HCF, which possesses enhanced electronic structure and ion transport path—can intercalate/de‐intercalate large amounts of proton at high rates. Ion‐induced transformation of magnetism, fast solid‐state proton transport, and reversible insertion/de‐insertion of protons lead to extremely excellent rate capacities and cycling stability for proton storage. An asymmetric pseudocapacitive proton supercapacitor (Cu0.82Co0.18HCF//WO3·nH2O) is fabricated with a voltage window of 1.7 V, delivering a maximum energy density of 35 Wh kg−1 and an energy density of 22 Wh kg−1 at a high power density of 26 kW kg−1. Combining systematical material design and mechanism study, this work not only broadens the preparation of electrode materials but also brings light to the construction of high‐performance devices for efficient proton storage. [ABSTRACT FROM AUTHOR]

Converting low-grade heat from environment into electricity shows great sustainability for mitigating the energy crisis and adjusting energy configurations. However, thermally rechargeable devices typically suffer from poor conversion efficiency when a semiconductor is employed. Breaking the convention of thermoelectric systems, we propose and demonstrate a new zinc ion thermal charging cell to generate electricity from low-grade heat via the thermo-extraction/insertion and thermodiffusion processes of insertion-type cathode (VO2-PC) and stripping/plating behaviour of Zn anode. Based on this strategy, an impressively high thermopower of ~12.5 mV K−1 and an excellent output power of 1.2 mW can be obtained. In addition, a high heat-to-current conversion efficiency of 0.95% (7.25% of Carnot efficiency) is achieved with a temperature difference of 45 K. This work, which demonstrates extraordinary energy conversion efficiency and adequate energy storage, will pave the way towards the construction of thermoelectric setups with attractive properties for high value-added utilization of low-grade heat. Low-grade heat conversion has recently emerged and displayed great promise in sustainable electronics and energy areas. Here, the authors propose a new zinc ion thermal charging cell with hybrid behaviours for high value-added conversion from heat to electricity. [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]

Zinc‐ion batteries (ZIBs) have been regarded as one of the most promising aqueous energy storage devices due to their low‐cost, high capacity, and intrinsic safety. However, the relatively low Coulombic efficiency caused by the dendrite formation and side reactions greatly hinders the rejuvenation of ZIBs. Here, an utterly simple approach by pencil drawing is employed to improve the poor performance of normal Zn anode and hinders the formation of passivated byproduct as well as serious dendrite growth. Significantly, the functional graphite layer can not only act as ions buffer, but also guide the uniform nucleation of Zn2+ in graphite voids. With such synergy effect, the graphite‐coated Zn anode (Zn–G) displays low overpotential, high reversibility, and dendrite‐free durability compared with the pristine Zn. Consequently, a low voltage hysteresis of ≈28 mV can be achieved and maintained over 200 h. Furthermore, the Zn–G anode is paired with a V2O5·xH2O cathode to construct a rechargeable ZIB. As‐assembled device can output high energy/power density of 324.3 Wh kg−1/3269.8 W kg−1 (based on the active mass loading in cathode) together with a capacity retention of ≈84% over 1500 cycles at a current density of 5 A g−1. [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]

Wearable electronic devices are the new darling of consumer electronics, and energy storage devices are an important part of them. Here, a wearable lithium‐sulfur (Li‐S) bracelet battery using three‐dimensional (3D) printing technology (additive manufacturing) is designed and manufactured for the first time. The bracelet battery can be easily worn to power the wearable device. The "additive" manufacturing characteristic of 3D printing provides excellent controllability of the electrode thickness with much simplified process in a cost‐effective manner. Due to the conductive 3D skeleton providing interpenetrating transmission paths and channels for electrons and ions, the 3D Li‐S battery can provide 505.4 mAh g−1 specific capacity after 500 cycles with an active material loading as high as 10.2 mg cm−1. The practicality is illustrated by wearing the bracelet battery on the wrist and illuminating the red light‐emitting diode. Therefore, the bracelet battery manufactured by 3D printing technology can address the needs of the wearable power supply. [ABSTRACT FROM AUTHOR]

Organic lithium ion batteries (LIBs) are considered as one of the next‐generation green electrochemical energy storage (EES) devices. However, obtaining both high capacity and long‐term cyclability is still the bottleneck of organic electrode materials for LIBs because of weak structural and chemical stability and low conductivity. Covalent organic frameworks (COFs) show potential to overcome these problems owing to its good stability and high capacity. Herein, the synthesis and characterization of two π‐conjugated COFs, derived from the Schiff‐base reaction of 2,4,6‐triaminopyrimidne (TM) respectively with 1,4‐phthalaldehyde (PA) and 1,3,5‐triformylbenzene (TB) by a mechanochemical process are presented. As anode materials for LIBs, the COFs exhibit favorable electrochemical performance with the highest reversible discharge capacities of up to 401.3 and 379.1 mAh g−1 at a high current density (1 A g−1), respectively, and excellent long‐term cyclability with 74.8 and 72.7 % capacity retention after 2000 cycles compared to the initial discharge capacities. [ABSTRACT FROM AUTHOR]

Abstract Using shell-like structures in lithium-ion battery (LIB) can limit the structural degradation/damage induced by the volumetric change during electrochemical cycling. In this work, we synthesize hollow Sn microspheres (Sn-HMSs) via a galvanic replacement reaction, and study the electrochemical performance of the lithium-ion cells with Sn-HMSs as the working electrode. The lithium-ion cells have a charge capacity of 205.9 mA h g−1 after 100 cycles at a current density of 100 mA g−1. In comparison with the charge capacities of 148 mA h g−1 of solid Sn nanospheres and 516.1 mA h g−1 of hollow Sn nanospheres, the results reported in this work reveal the importance of shell-like structures in the retention of the energy storage for LIBs and the size effect on the energy storage. The smaller the hollow Sn spheres, the better is the cycle performance. There are two modes of structural degradation/damage contributing to the capacity loss during electrochemical cycling; one is the disintegration of the Sn-HMSs, and the other is the fracturing of the electrode layer. Highlights • Sn in the Sn-HMSs exhibits tetragonal crystal structure with the size of 3–8 μm. • There are multi-step reactions involving the lithiation and delithiation. • There are two modes of structural degradation/damage contributing to capacity loss. • One structural degradation mode is the disintegration of the Sn-HMSs. • The other structural degradation is the fracturing of the electrode layer. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs) are a promising alternative to lithium-ion batteries for large-scale energy storage applications. The intriguing 2D transition-metal carbides/carbonitrides, also called MXenes, are increasingly being investigated as anodes as for SIB applications, owing to the merits of their metallic conductivity, low diffusion barrier for Na+, and good mechanical properties. However, the issue of low specific capacity has proven to be a difficult challenge to overcome. Herein, we synthesize a composite of MoS2/Ti3C2T x to improve the ion accessibility of MXene layers by increasing the interlayer space and boost its specific capacity, where the MoS2 nanosheets are intercalated between Ti3C2T x layers through a hydrothermal route. When tested as a SIB anode, the MoS2/Ti3C2T x composite yielded a high specific capacity of 250.9 mAh g−1 over 100 cycles. More remarkably, the MoS2/Ti3C2T x electrode displayed an exceeding rate performance with a capacity of 162.7 mAh g−1 at 1 A g−1. [ABSTRACT FROM AUTHOR]

Metal-organic framework (MOF)-derived carbon materials exhibit large surface areas, but dominant micropore characteristics and uncontrollable dimensions. Herein, we propose a self-sacrificial template-directed synthesis method to engineer the porous structure and dimensions of MOF-derived carbon materials. A porous zinc oxide (ZnO) nanosheet solid is selected as the self-sacrificial template and two-dimensional (2D) nanostructure-directing agent to prepare 2D ZIF-8-derived carbon nanosheets (ZCNs). The as-prepared ZCN materials exhibit a large surface area with hierarchical porosity. These intriguing features render ZCN materials advanced electrode materials for electrochemical energy-storage devices, demonstrating large ion-accessible surface area and high ion-/electron-transport rates. This self-sacrificial template-directed synthesis method offers new avenues for rational engineering of the porous structure and dimensions of MOF-derived porous carbon materials, thus exploiting their full potential for electrochemical energy-storage devices. [ABSTRACT FROM AUTHOR]

To push the energy density limit of supercapacitors, a new class of electrode materials with favorable architectures is strongly needed. Binary metal sulfides hold great promise as an electrode material for high-performance energy storage devices because they offer higher electrochemical activity and higher capacity than mono-metal sulfides. Here, the rational design and fabrication of NiCo2S4 nanosheets supported on nitrogen-doped carbon foams (NCF) is presented as a novel flexible electrode for supercapacitors. A facile two-step method is developed for growth of NiCo2S4 nanosheets on NCF with robust adhesion, involving the growth of Ni-Co precursor and subsequent conversion into NiCo2S4 nanosheets through sulfidation process. Benefiting from the compositional features and 3D electrode architectures, the NiCo2S4/NCF electrode exhibits greatly improved electrochemical performance with ultrahigh capacitance (877 F g−1 at 20 A g−1) and excellent cycling stability. Moreover, a binder-free asymmetric supercapacitor device is also fabricated by using NiCo2S4/NCF as the positive electrode and ordered mesoporous carbon (OMC)/NCF as the negative electrode; this demonstrates high energy density (≈45.5 Wh kg−1 at 512 W kg−1). [ABSTRACT FROM AUTHOR]

Sodium-ion batteries with good electrochemical performance are of great significance for grid-scale energy storage applications. Herein, an aqueous rechargeable Na-ion battery has been fabricated with multiwalled carbon nanotube (MWNT)-containing NaTi2(PO4)3/MWNTs nanocomposites as the anode and Na0.44MnO2 nanorods as the cathode in a 1 M aqueous Na2SO4 electrolyte and the device was carefully studied. Owing to the open framework structures (containing large interstitial sites) that both NaTi2(PO4)3 and Na0.44MnO2 possess, the fast Na-ions will facilitate free transport. Benefiting from their unique structural features, the aqueous battery system exhibited an average charge and discharge voltage of approximately 1.1 V, a high energy density of 58.7 Wh kg−1 in terms of total electroactive materials, and could deliver a reversible capacity of approximately 50 mAh g−1 after 300 cycles at 2 C rate; the corresponding coulombic efficiency was nearly constant at approximately 95 %. These results, together with the safety and cost perspectives of aqueous electrolytes indicated that the aqueous Na-ion battery may be a good candidate for safe, inexpensive, high-power energy storage systems. [ABSTRACT FROM AUTHOR]

Porous nitrogen-doped carbon nanotubes (PNCNTs) with a high specific surface area (1765 m2 g−1) and a large pore volume (1.28 cm3 g−1) have been synthesized from a tubular polypyrrole (T-PPY). The inner diameter and wall thickness of the PNCNTs are about 55 nm and 22 nm, respectively. This material shows extremely promising properties for both supercapacitors and for encapsulating sulfur as a superior cathode material for high-performance lithium-sulfur (Li-S) batteries. At a current density of 0.5 A g−1, PNCNT presents a high specific capacitance of 210 F g−1, as well as excellent cycling stability at a current density of 2 A g−1. When the S/PNCNT composite was tested as the cathode material for Li-S batteries, the initial discharge capacity was 1341 mAh g−1 at a current rate of 1 C and, even after 50 cycles at the same rate, the high reversible capacity was retained at 933 mAh g−1. The promising electrochemical energy-storage performance of the PNCNTs can be attributed to their excellent conductivity, large surface area, nitrogen doping, and unique pore-size distribution. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) hierarchical carbon-sulfur nanocomposite that is useful as a high-performance cathode for rechargeable lithium-sulfur batteries is reported. The 3D hierarchically ordered porous carbon (HOPC) with mesoporous walls and interconnected macropores was prepared by in situ self-assembly of colloidal polymer and silica spheres with sucrose as the carbon source. The obtained porous carbon possesses a large specific surface area and pore volume with narrow mesopore size distribution, and acts as a host and conducting framework to contain highly dispersed elemental sulfur. Electrochemical tests reveal that the HOPC/S nanocomposite with well-defined nanostructure delivers a high initial specific capacity up to 1193 mAh g−1 and a stable capacity of 884 mAh g−1 after 50 cycles at 0.1 C. In addition, the HOPC/S nanocomposite exhibits high reversible capacity at high rates. The excellent electrochemical performance is attributed exclusively to the beneficial integration of the mesopores for the electrochemical reaction and macropores for ion transport. The mesoporous walls of the HOPC act as solvent-restricted reactors for the redox reaction of sulfur and aid in suppressing the diffusion of polysulfide species into the electrolyte. The 'open' ordered interconnected macropores and windows facilitate transportation of electrolyte and solvated lithium ions during the charge/discharge process. These results show that nanostructured carbon with hierarchical pore distribution could be a promising scaffold for encapsulating sulfur to approach high specific capacity and energy density with long cycling performance. [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 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]

Emerging ionic thermoelectric devices (i-TEs), with synergistic effect of thermogalvanic effect and thermo-diffusion effect, are promising devices to achieve heat to electricity. We report a zinc-iodine thermal charging cell (ZITCC) enabled by cost-efficient electrolytes for low-grade heat harvesting. Efficient functional electrolytes are obtained through optimization from Zn(NO 3) 2 , Zn(CH 3 COO) 2 and ZnSO 4 electrolytes and introducing redox species (I−/I 3 −). The ZITCCs generate electricity through thermo-diffusion effect of electrolyte ions, as well as the thermogalvanic effect involving I− to I 3 − conversion and Zn plating, enabling efficient heat-to-electricity conversion. The Seebeck coefficient of 19.2 mV K−1, a high output voltage of ∼1 V and superior normalized maximum power density of 0.44 mW m−2 K−2 is obtained at temperature difference of 15 K. Meanwhile, ZITCCs have good energy storage capacity. In addition, a quasi-solid-state device delivers an 8.5 mW m−2 output power and impressive performance at temperature difference of 8 K can be acquired. This work provides a good strategy for the design of high-Seebeck coefficient, cost-effective i-TEs for low-grade heat harvesting. [Display omitted] • ZnSO 4 electrolyte was optimized from low-cost regular zinc salt electrolytes. • Redox species (I−/I 3 −) additives enhanced the thermogalvanic effect. • A high-performance zinc - iodine thermal charging cell was constructed. [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]

Abstract All-solid-state batteries have shown excellent safety property, making them promising candidates for large scale energy storage applications. Solid-state electrolyte (SSE) with high ionic conductivity and chemical stability is crucial for practical application of all-solid-state batteries. Herein, a cubic perovskite-type SSE with an optimal composition of Na 1/3 La 1/3 Sr 1/3 ZrO 3 has been synthesized by a conventional solid-state reaction, which was investigated by XRD, SEM and electrochemical impedance spectroscopy. Na 1/3 La 1/3 Sr 1/3 ZrO 3 (NLSZO) shows a high Na-ion conductivity of 1.025 × 10−5 S cm−1 at 25 °C. The effects of composition and sintering temperature on the lattice parameter, relative density and Na-ion conductivity of SSE have been explored in detail. The increase of Sr doping amount in NLSZO and sintering temperature leads to an augment of lattice parameter and densification of SSE, which contributed to an enhanced ionic conductivity. Highlights • A new-type Na-ion solid state electrolyte is synthesized by solid state reaction. • Sr-doping is performed to improve the ion conductivity of solid state electrolyte. • The effects of composition and synthetic process on conductivity are investigated. • A conductivity of 1.025 × 10−5 Scm−1 is achieved by optimization of synthetic process. [ABSTRACT FROM AUTHOR]

The TiN coated NaTi 2 (PO 4 ) 3 with high electrochemical performance as anode materials for aqueous sodium-ion batteries were synthesized successfully by solvothermal routine and subsequent nitriding process in the presence of ammonia. The nitriding process would not change the crystal structure of NaTi 2 (PO 4 ) 3 . However, the Ti 4+ in the material can be reduced to Ti 3+ , and the nitrogen atom can be doped into the material, forming a TiN layer on the surface of the material, which significantly increased the electronic conductivity of NaTi 2 (PO 4 ) 3 material. By adjusting nitriding time, we have prepared the best nitriding material and the effect of nitriding on NaTi 2 (PO 4 ) 3 materials has been clearly clarified. The rate capacity and cyclic performance of the TiN tailored NaTi 2 (PO 4 ) 3 have been greatly improved, which is much better than the pristine phase . The initial capacity of the TiN tailored NaTi 2 (PO 4 ) 3 can reach 131.9 mAh g −1 , and it can still keep 92 mAh g −1 after 100 cycles at 2 C. [ABSTRACT FROM AUTHOR]

Multifarious layered materials have received extensive concern in the field of energy storage due to their distinctive two-dimensional (2D) structure. However, the natural tendency to be re-superimposed and the inherent disadvantages of a single 2D material significantly limit their performance. In this work, the delaminated Ti 3 C 2 T x (d-Ti 3 C 2 T x )/cobalt-aluminum layered double hydroxide (Ti 3 C 2 T x /CoAl-LDH) composites are prepared by layer-by-layer self-assembly driven by electrostatic interaction. The alternate Ti 3 C 2 T x and CoAl-LDH layers prevent each other from restacking and the obtained Ti 3 C 2 T x /CoAl-LDH heterostructure combine the advantages of high electron conductivity of Ti 3 C 2 T x and high electrochemical activity of CoAl-LDH, thus effectively improving the electrochemical reactivity of electrode materials and accelerating the kinetics of Faraday reaction. As a consequence, as a cathode for alkaline hybrid battery, the Ti 3 C 2 T x /CoAl-LDH electrode exhibits a high specific capacity of 106 mAh g −1  at a current density of 0.5 A g −1 and excellent rate capability (78% at 10 A g −1 ), with an excellent cycling stability of 90% retention after 5000 cycles at 4 A g −1 . This work provides an alternative route to design advanced 2D electrode materials, thus exploiting their full potentials for alkaline hybrid batteries. [ABSTRACT FROM AUTHOR]

Given the safety and cost involved, aqueous electrolyte is an extremely attractive candidate for large-scale energy storage systems. However, limited electrochemical stability window of water (decomposition potential <1.23 V) usually confines the energy density of aqueous energy storage systems. Herein, an aqueous electrolyte based on NaClO 4 solution with a high concentration of 17 m is demonstrated to enlarge the practical stability window to approximately 2.75 V, because the scarcity of free water molecules in high salt concentration contributes to their inactivity. An aqueous sodium-ion hybrid capacitor is assembled by using the electrolyte and could be operated at a large voltage of 2.0 V, in which aromatic polyimide (PI) is used as anode material and ultrahigh specific surface PI derived porous carbon microspheres as cathode. This enhanced electrochemical window of the aqueous electrolyte ensures that the sodium-ion capacitor delivers an energy density of 65.1 Wh kg −1 with high power density and good cycle stability. Most importantly, compared to most used host materials with conventional intercalation mechanisms, fast reaction kinetics and structural insensitivity of PI to the ion radius are responsible for the excellent sodium storage properties. [ABSTRACT FROM AUTHOR]

Li 4 Ti 5 O 12 with long cycling life has been deemed to be one of the most promising anode materials for lithium ion battery. Nevertheless, poor electronic conductivity impedes its application for energy storage. Meanwhile MXene possesses high electrical conductivity and moderate electrochemical energy storage. Herein, we develop a novel strategy for the in-situ synthesis of layered-stacked Li 4 Ti 5 O 12 -MXene composite. The synergistic effect of Li 4 Ti 5 O 12 and MXene greatly improved the electrochemical properties of Li 4 Ti 5 O 12 -MXene composite. At a high current density of 10 A g − 1 , a high discharge capacity of 116 mAh g − 1 can be achieved. Moreover, a high discharge capacity of 178 mAh g − 1 after 500 cycles can be maintained at a current density of 5 A g − 1 . This work demonstrates a scalable route to assemble MXene-derived Ti-based materials for high-performance electrochemical energy storage applications. [ABSTRACT FROM AUTHOR]

Bacterial cellulose (BC), a typical biomass prepared from the microbial fermentation process, has been proved that it can be an ideal platform for design of three-dimensional (3D) multifunctional nanomaterials in energy storage and conversion field. Here we developed a simple and general silica-assisted strategy for fabrication of interconnected 3D meso-microporous carbon nanofiber networks by confine nanospace pyrolysis of sustainable BC, which can be used as binder-free electrodes for high-performance supercapacitors. The synthesized carbon nanofibers exhibited the features of interconnected 3D networks architecture, large surface area (624 m 2 g −1 ), mesopores-dominated hierarchical porosity, and high graphitization degree. The as-prepared electrode (CN-BC) displayed a maximum specific capacitance of 302 F g −1 at a current density of 0.5 A g −1 , high-rate capability and good cyclicity in 6 M KOH electrolyte. This work, together with cost-effective preparation strategy to make high-value utilization of cheap biomass, should have significant implications in the green and mass-producible energy storage. [ABSTRACT FROM AUTHOR]

High value-added utilization of ubiquitous low-grade heat shows great importance to energy regulation. liquid thermocell is considered as promising candidate for converting heat into electricity due to its high Seebeck coefficient and facile operation. However, the challenging integration of dozens of tiny devices is still required to generate a useful voltage, which greatly blocks the development of thermocells. Here, a well-defined nitrogen-doped hierarchical porous carbon (NHPC) obtained by self-template carbonization and alkaline activation is employed to construct high-performance zinc ion thermal charging supercapacitors (ZTSC) for the integration of energy conversion and storage. Significantly, continuous architecture of NHPC can enlarge the electrochemical active surface and shorten the diffusion pathways of electrolyte ions. Consequently, a high energy/power density of 71.8 Wh kg−1/10.3 kW kg−1 can be achieved. Moreover, NHPC based ZTSC can output an attractive voltage of 1.16 V, a high thermopower of 31.4 mV K−1, and a superior normalized power density of 15.3 mW m−2 K−2 with a temperature difference of 27 K. This work not only provides a facile strategy to prepare promising carbon materials, but also demonstrates the possibility of hybrid supercapacitors for heat-to-current conversion and storage. [Display omitted] • A facile strategy is proposed to form N-doped hierarchical porous carbon (NHPC). • The NHPC shows high capacitance and good rate capability in energy storage. • A high-performance zinc thermal charging supercapacitor is constructed. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) titanium dioxide@germanium (TiO2@Ge) core-shell nanorod arrays on carbon textiles are fabricated by a facile two-step method and further investigated as flexible electrode for Li-ion batteries (LIBs). The synthesis of TiO2@Ge composite involves the hydrothermal growth of TiO2 nanorod arrays on carbon textiles and a subsequent coat with a thin layer of germanium with radio frequency (RF) magnetron sputtering. The TiO2 nanorod arrays can effectively not only increase the unit mass loading as a role of skeleton but also remarkably enhance the electrical conductivity via control the lithiation/delithiation voltage in the range of 0.01-1.0 V, where TiO2 can be in situ lithiated to LixTiO2 after the first discharge cycle. Moreover, each TiO2@Ge nanorod has enough space to accommodate the large volume expansion of Ge during charge and discharge cycles. Benefiting from unique electrode architectures, this additive free, self-supported electrode exhibits the high reversible capacity, outstanding rate capability, and the extremely long cycling stability even at a high rate (700.3 mAh g−1 is still retained at 5 A g−1 after 600 cycles). [ABSTRACT FROM AUTHOR]

The exploration of thermally chargeable supercapacitors has gained intensive interest. However, their practical application is still restricted by complex integration, poor Seebeck coefficient, and unsatisfactory conversion efficiency. Herein, we report a high-performance device with a simplified symmetric configuration based on activated carbon derived from elm bark mucus. Due to high specific surface area, hierarchical porosity, and moderate surface chemistry, such system displays excellent electrochemical properties such as high capacitance, rate capability and thermoelectrical behavior. When coupling with a concentrated electrolyte (26 m KOAc), a 2.0 V symmetric supercapacitor can be fabricated and a maximum energy density of 33.6 Wh kg−1 at power density of 500 W kg−1. A high-power density of 20 kW kg−1 also can be achieved at 21.7 Wh kg−1. Moreover, thermally rechargeable devices with quasi solid-state electrolyte exhibit a high open circuit voltage of ∼24.02 mV and a considerable Seebeck coefficient of about 1.97 mV K−1, indicating satisfying thermoelectrical performances. This work not only demonstrates the applicability of elm bark mucus-derived carbon as advanced materials for energy application, but also provides a new perspective for the development of multifunctional devices. [Display omitted] • A facile approach is proposed to prepare biomass-derived porous carbon. • The AMPC-3 material exhibits satisfactory electrochemical performance. • A high-performance thermally rechargeable supercapacitor is constructed. [ABSTRACT FROM AUTHOR]

Abstract: A flexible graphene/multiwalled carbon nanotube (GN/MWCNT) film has been fabricated by flow-directed assembly from a complex dispersion of graphite oxide (GO) and pristine MWCNTs followed by the use of gas-based hydrazine to reduce the GO into GN sheets. The GN/MWCNT (16wt.% MWCNTs) film characterized by Fourier transformation infrared spectra, X-ray diffraction and scanning electron microscope has a layered structure with MWCNTs uniformly sandwiched between the GN sheets. The MWCNTs in the obtained composite film not only efficiently increase the basal spacing but also bridge the defects for electron transfer between GN sheets, increasing electrolyte/electrode contact area and facilitating transportation of electrolyte ion and electron into the inner region of electrode. Electrochemical data demonstrate that the GN/MWCNT film possesses a specific capacitance of 265Fg−1 at 0.1Ag−1 and a good rate capability (49% capacity retention at 50Ag−1), and displays an excellent specific capacitance retention of 97% after 2000 continuous charge/discharge cycles. The results of electrochemical measurements indicate that the freestanding GN/MWCNT film has a potential application in flexible energy storage devices. [Copyright &y& Elsevier]

Abstract: Manganese dioxide/multiwalled carbon nanotubes (MnO2/MWCNTs) were synthesized by chemically depositing MnO2 onto the surface of MWCNTs wrapped with poly(sodium-p-styrenesulfonate). Then, polyaniline (PANI) with good supercapacitive performance was further coated onto the MnO2/MWCNTs composite to form PANI/MnO2/MWCNTs organic–inorganic hybrid nanoarchitecture. Electrochemical performance of the hybrid in Na2SO4–H2SO4 mixed acidic electrolytes was evaluated by cyclic voltammetry (CV) and chronopotentiometry (CP) in detail. Comparative electrochemical tests revealed that the hybrid nanoarchitecture could operate in the acidic medium due to the protective modification of PANI coating layer onto the MnO2/MWCNTs composite, and that its electrochemical behavior was greatly dependent upon the concentration of protons in the acidic electrolytes. Here, PANI not only served as a physical barrier to restrain the underlying MnO2/MWCNTs composite from reductive-dissolution process so as to make the novel ternary hybrid material work in acidic medium to enhance the utilization of manganese oxide as much as possible, but also was another electroactive material for energy storage in the acidic mixed electrolytes. It was due to the existence of PNAI layer that an even larger specific capacitance (SC) of 384Fg−1 and a much better SC retention of 79.9% over 1000 continuous charge/discharge cycles than those for the MnO2/MWCNTs nanocomposite were delivered for the hybrid in the optimum 0.5M Na2SO4–0.5M H2SO4 mixed acidic electrolyte. [Copyright &y& Elsevier]

Low-grade waste heat, which exhibits widely in industrial production and daily life, shows great promise for smart electronics and sensors, but we always ignore this energy. Recently, developing thermoelectric conversion devices becomes a popular subject. Unfortunately, the relatively low Seebeck coefficient of current devices limits their further applications. Thus, it should give priority to matching suitable electrolyte and constructing high-rate system. Here, we employ a series of common neutral electrolytes to optimize the energy storage behavior towards high capacitance and rate capability. As a result, the commercial carbon electrode displays a high specific capacitance of 220.8 F g−1 at a current density of 1 A g−1 and a good retention of 61.2% even at a high rate of 20 A g−1 in 1.0 mol L−1 potassium nitrate electrolyte. Meanwhile, the assembled symmetric supercapacitor can output the maximum energy/power density of 13.1 Wh kg−1/15.7 kW kg−1 based on the active material, together with an excellent durability (~109% capacitance retention over 10,000 cycles at 5 A g−1). Besides, a thermally chargeable supercapacitor exhibits a satisfying output potential of 1.21 mV K−1 under optimized cases. Significantly, the potential value is highly determined by temperature gradient. Image 1 • KNO 3 electrolyte was optimized from common neutral solutions. • The YP-80F shows high capacitance and fast kinetics in KNO 3 electrolyte. • A high-performance thermally chargeable supercapacitor was constructed. [ABSTRACT FROM AUTHOR]