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Rechargeable aqueous zinc-ion batteries (ZIBs) have become a research hotspot in recent years, due to their huge potential for high-energy, fast-rate, safe and low-cost energy storage. To realize good electrochemical properties of ZIBs, cathode materials with prominent Zn2+ storage capability are highly needed. Herein, we report a promising ZIB cathode material based on electrochemically induced transformation of vanadium oxides. Specifically, K2V6O16·1.5H2O nanofibers were synthesized through a simple stirring method at near room temperature and then used as cathode materials for ZIBs in different electrolytes. The cathode presented superior Zn2+ storage capability in Zn(OTf)2 aqueous electrolyte, including high capacity of 321 mAh/g, fast charge/discharge ability (96 mAh/g delivered in 35 s), high energy density of 235 Wh/kg and good cycling performance. Mechanism analysis evidenced that in Zn(OTf)2 electrolyte, Zn2+ intercalation in the first discharge process promoted K2V6O16·1.5H2O nanofibers to transform into Zn3+xV2O7(OH)2·2H2O nanoflakes, and the latter served as the Zn2+-storage host in subsequent charge/discharge processes. Benefiting from open-framework crystal structure and sufficiently exposed surface, the Zn3+xV2O7(OH)2·2H2O nanoflakes exhibited high Zn2+ diffusion coefficient, smaller charge-transfer resistance and good reversibility of Zn2+ intercalation/de-intercalation, thus leading to superior electrochemical performance. While in ZnSO4 aqueous electrolyte, the cathode material cannot sufficiently transform into Zn3+xV2O7(OH)2·2H2O, thereby corresponding to inferior electrochemical behaviors. Underlying mechanism and influencing factors of such a transformation phenomenon was also explored. This work not only reports a high-performance ZIB cathode material based on electrochemically induced transformation of vanadium oxides, but also provides new insights into Zn2+-storage electrochemistry.

Few-layer Ti3C2Tx MXene is synthesized from multi-layered Ti3C2Tx via a flash freezing-assisted delamination process. During the flash freezing process, the water molecules in the interlayers of multi-layered MXene are induced to rearrange and produce volume expansion, thus notably expand the MXenes’ interlayer distance to form few-layer MXene. The synthesized few-layer Ti3C2Tx MXene nanosheets display a very small thickness (less than 5 Ti3C2 atom-layers) and expanded interlayer spacing. Consequently, the few-layer Ti3C2Tx exhibits enhanced capacitance (255 F g−1 vs. 177 F g−1 for the multi-layered Ti3C2Tx) and significantly optimized rate capability (150 F g−1 at 200 mV s−1 vs. 25 F g−1 for the multi-layered Ti3C2Tx), because redox-active sites in the few-layer MXene are easily accessible to electrolyte ions. Moreover, an asymmetric supercapacitor is constructed using the few-layer Ti3C2Tx negative electrode and an activated carbon fiber positive electrode. The asymmetric supercapacitor presents a high energy density of 17.9 Wh kg−1 and a high power density of 14 kW kg−1, which is inseparable from its wide voltage window of 1.4 V and the good rate performance of the few-layer Ti3C2Tx MXene electrode. Overall, the flash freezing-assist delamination provides an effective and environmental-friendly strategy to synthesize few-layer MXene materials for high-rate electrochemical energy storage.

Highlights This work starts the research of pseudocapacitive oxide materials for multivalent Zn2+ storage.The constructed RuO2·H2O||Zn systems exhibit outstanding electrochemical performance, including a high discharge capacity, ultrafast charge/discharge capability, and excellent cycling stability.The redox pseudocapacitive behavior of RuO2·H2O for Zn2+ storage is revealed. Electronic supplementary material The online version of this article (10.1007/s40820-019-0328-3) contains supplementary material, which is available to authorized users., Rechargeable aqueous zinc-ion hybrid capacitors and zinc-ion batteries are promising safe energy storage systems. In this study, amorphous RuO2·H2O for the first time was employed to achieve fast and ultralong-life Zn2+ storage based on a pseudocapacitive storage mechanism. In the RuO2·H2O||Zn zinc-ion hybrid capacitors with Zn(CF3SO3)2 aqueous electrolyte, the RuO2·H2O cathode can reversibly store Zn2+ in a voltage window of 0.4–1.6 V (vs. Zn/Zn2+), delivering a high discharge capacity of 122 mAh g−1. In particular, the zinc-ion hybrid capacitors can be rapidly charged/discharged within 36 s with a very high power density of 16.74 kW kg−1 and a high energy density of 82 Wh kg−1. Besides, the zinc-ion hybrid capacitors demonstrate an ultralong cycle life (over 10,000 charge/discharge cycles). The kinetic analysis elucidates that the ultrafast Zn2+ storage in the RuO2·H2O cathode originates from redox pseudocapacitive reactions. This work could greatly facilitate the development of high-power and safe electrochemical energy storage. Electronic supplementary material The online version of this article (10.1007/s40820-019-0328-3) contains supplementary material, which is available to authorized users.

Hybrid metal-ion capacitors are designed to promote the energy density of supercapacitors with less sacrifice of power density. Zinc-ion hybrid supercapacitor, based on the multivalent ion storage principle, is a kind of energy storage device in which both the high energy density and power density can be achieved. Here, we propose a new configuration of zinc-ion hybrid supercapacitors composed of mild aqueous ZnSO4 electrolyte, activated carbon (AC) anode and V2O5 cathode. The operating voltage of the hybrid supercapacitor can reach to 2 V in the aqueous electrolyte when the mass ratio of AC to V2O5 is 1:1. The maximum energy density of zinc-ion hybrid capacitor is about 3.9 times higher than that of AC symmetric supercapacitor, while its maximum power density is 1.7 times higher than that of zinc-ion battery. The capacity retention of the hybrid supercapacitors is 97.3% over 6000 charge–discharge cycles at 0.5 A g−1. Compared with MnO2 zinc-ion hybrid supercapacitors system, the stable nature of V2O5 allows new zinc-ion hybrid supercapacitors system to achieve a better cycling performance. The unique electrochemical performance, low cost and high safety of the new zinc-ion hybrid supercapacitor endow it with a very wide range of applications in consumer electronics and stationary energy storage.

© 2019 American Chemical Society. Zinc ion batteries (ZIBs) have attracted extensive attention in recent years, benefiting from their high safety, eco-friendliness, low cost, and high energy density. Although many cathode materials for ZIBs have been developed, the poor stability of zinc anodes caused by uneven deposition/stripping of zinc has inevitably limited the practical application of ZIBs. Herein, we report a highly stable 3D Zn anode prepared by electrodepositing Zn on a chemically etched porous copper skeleton. The inherent excellent electrical conductivity and open structure of the 3D porous copper skeleton ensure the uniform deposition/stripping of Zn. The 3D Zn anode exhibits reduced polarization, stable cycling performance, and almost 100% Coulombic efficiency as well as fast electrochemical kinetics during repeated Zn deposition/stripping processes for 350 h. Furthermore, full cells with a 3D Zn anode, ultrathin MnO2 nanosheet cathode, and Zn2+-containing aqueous electrolyte delivered a record-high capacity of 364 mAh g-1 at a current density of 0.1 A g-1 and good cycling stability with a retained capacity of 173 mAh g-1 after 300 charge/discharge cycles at 0.4 A g-1. This work provides a pathway for developing high-performance ZIBs.

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim MnO2 is a traditional cathode material for aqueous zinc-ion battery (ZIB). However, its extensive use is limited by its poor conductivity and cycling performance. Design of binary or ternary MnO2 composites is a useful way to enhance the performance of MnO2. At first, a series of binary MnO2/carbon nanotube (CNT) composites with different CNT contents were synthesized by a facile co-precipitation method. The effect of CNT content on the properties of binary composites was investigated. In addition, the ternary MnO2/CNT/polyaniline (PANI) composites were prepared to investigate the effect of unitary, binary and ternary composites on the MnO2. The results show that an appropriate content of CNT decreases the charge transfer resistance of the composite leading to a good electrochemical performance. The addition of PANI stabilizes the cycle performance of the composite at a cost of a slight decrease in the specific capacity.

Highlights A surface engineering strategy was proposed to design hierarchically porous structure on fibrous carbon cathodes with O/N heteroatom functional groups.High-energy and anti-self-discharge Zn-ion hybrid supercapacitors (ZHSs) were realized.ZHS electrochemistry was investigated and new insights were provided. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00625-3., Aqueous Zn-ion hybrid supercapacitors (ZHSs) are increasingly being studied as a novel electrochemical energy storage system with prominent electrochemical performance, high safety and low cost. Herein, high-energy and anti-self-discharge ZHSs are realized based on the fibrous carbon cathodes with hierarchically porous surface and O/N heteroatom functional groups. Hierarchically porous surface of the fabricated free-standing fibrous carbon cathodes not only provides abundant active sites for divalent ion storage, but also optimizes ion transport kinetics. Consequently, the cathodes show a high gravimetric capacity of 156 mAh g−1, superior rate capability (79 mAh g−1 with a very short charge/discharge time of 14 s) and exceptional cycling stability. Meanwhile, hierarchical pore structure and suitable surface functional groups of the cathodes endow ZHSs with a high energy density of 127 Wh kg−1, a high power density of 15.3 kW kg−1 and good anti-self-discharge performance. Mechanism investigation reveals that ZHS electrochemistry involves cation adsorption/desorption and Zn4SO4(OH)6·5H2O formation/dissolution at low voltage and anion adsorption/desorption at high voltage on carbon cathodes. The roles of these reactions in energy storage of ZHSs are elucidated. This work not only paves a way for high-performance cathode materials of ZHSs, but also provides a deeper understanding of ZHS electrochemistry. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00625-3.

Highlights Various MOF materials were synthesized and investigated as ZIB cathodes.A long-term stable ZIF-8@Zn anode was proposed by coating ZIF-8 material on the surface of zinc foils.High-performance aqueous ZIBs were constructed using the Mn(BTC) cathode and the ZIF-8@Zn anode. Electronic supplementary material The online version of this article (10.1007/s40820-020-00487-1) contains supplementary material, which is available to authorized users., Rechargeable aqueous zinc-ion batteries (ZIBs) have been gaining increasing interest for large-scale energy storage applications due to their high safety, good rate capability, and low cost. However, the further development of ZIBs is impeded by two main challenges: Currently reported cathode materials usually suffer from rapid capacity fading or high toxicity, and meanwhile, unstable zinc stripping/plating on Zn anode seriously shortens the cycling life of ZIBs. In this paper, metal–organic framework (MOF) materials are proposed to simultaneously address these issues and realize high-performance ZIBs with Mn(BTC) MOF cathodes and ZIF-8-coated Zn (ZIF-8@Zn) anodes. Various MOF materials were synthesized, and Mn(BTC) MOF was found to exhibit the best Zn2+-storage ability with a capacity of 112 mAh g−1. Zn2+ storage mechanism of the Mn(BTC) was carefully studied. Besides, ZIF-8@Zn anodes were prepared by coating ZIF-8 MOF material on Zn foils. Unique porous structure of the ZIF-8 coating guided uniform Zn stripping/plating on the surface of Zn anodes. As a result, the ZIF-8@Zn anodes exhibited stable Zn stripping/plating behaviors, with 8 times longer cycle life than bare Zn foils. Based on the above, high-performance aqueous ZIBs were constructed using the Mn(BTC) cathodes and the ZIF-8@Zn anodes, which displayed an excellent long-cycling stability without obvious capacity fading after 900 charge/discharge cycles. This work provides a new opportunity for high-performance energy storage system. Electronic supplementary material The online version of this article (10.1007/s40820-020-00487-1) contains supplementary material, which is available to authorized users.

With rapid development of portable electronics and electric vehicles, high-performance energy storage devices are urgently needed; however, the existing energy storage systems often have some deficiency, such as low energy for supercapacitors, security risks for lithium-ion batteries and poor cycling stability for alkaline zinc/manganese dioxide batteries. Here we report a novel energy storage system of zinc-ion hybrid supercapacitors (ZHSs), in which activated carbon materials, Zn metal and ZnSO4 aqueous solution serve as cathode, anode and electrolyte, respectively. Reversible ion adsorption/desorption on AC cathode and Zn2+ deposition/stripping on Zn anode enable the ZHSs to repeatedly and rapidly store/deliver electrical energy, accompanying with a capacity of 121 mAh g−1 (corresponding to an energy of 84 Wh kg−1), a very large power output of 14.9 kW kg−1 and an excellent cycling stability with 91% capacity retention over 10000 cycles. The extremely safe, high-rate and ultralong-life ZHSs are believed to provide new options for next-generation energy storage devices.

© 2018 American Chemical Society. Polymorphous supercapacitors were constructed from flexible three-dimensional carbon network/polyaniline (PANI)/MnO2 composite textile electrodes. The flexible textile electrodes were fabricated through a layer-by-layer construction strategy: PANI, carbon nanotubes (CNTs), and MnO2 were deposited on activated carbon fiber cloth (ACFC) in turn through an electropolymerization process, "dipping and drying" method, and in situ chemical reaction, respectively. In the fabricated ACFC/PANI/CNTs/MnO2 textile electrodes, the ACFC/CNT hybrid framework serves as a porous and electrically conductive 3D network for the rapid transmission of electrons and electrolyte ions, where ACFC, PANI, and MnO2 are high-performance supercapacitor electrode materials. In the electrolyte of H2SO4 solution, the textile electrode-based symmetric supercapacitor delivers superior areal capacitance, energy density, and power density of 4615 mF cm-2 (for single electrode), 157 μW h cm-2, and 10372 μW cm-2, respectively, whereas asymmetric supercapacitor assembled with the prepared composite textile as the positive electrode and ACFC as the negative electrode exhibits an improved energy density of 413 μW h cm-2 and a power density of 16120 μW cm-2. On the basis of the ACFC/PANI/CNTs/MnO2 textile electrodes, symmetric and asymmetric solid-state textile supercapacitors with a PVA/H2SO4 gel electrolyte were also produced. These solid-state textile supercapacitors exhibit good electrochemical performance and high flexibility. Furthermore, flexible solid-state fiber-like supercapacitors were prepared with fiber bundle electrodes dismantled from the above composite textiles. Overall, this work makes a meaningful exploration of the versatile applications of textile electrodes to produce polymorphous supercapacitors.

A multi hierarchical construction is designed for flexible supercapacitor electrodes. Specifically, we chose activated carbon fiber cloth (ACFC) as flexible substrates, deposited polyaniline (PANI) on fiber surface first, then constructed continuous carbon nanotube (CNT) networks between fibers and finally deposited PANI on the CNT networks to obtain ACFC/PANI/CNT/PANI textile electrodes. Repeated deposition of PANI and application of ACFC substrate lead to high content of electrochemically active materials ( i.e. , PANI and activated carbon fiber); meanwhile, these active materials are located in different locations in the electrodes (fiber itself, fiber surface and the space between fibers), thus avoiding serious aggregation. The fabricated electrodes exhibit superior capacitive performances: areal capacitance, energy density and power density are 4039 mF cm −2 , 131 μW h cm −2 and 11424 μW cm −2 , respectively, remarkably higher than those of previously reported flexible supercapacitor electrodes; our electrodes also have good cycling stability and flexibility. Furthermore, high-performance thick electrodes (capacitance: 7804 mF cm −2 ; energy output: 214 μW h cm −2 ) and flexible fiber-like electrodes (capacitance: 805 mF cm −2 ; energy density: 23 μW h cm −2 ) are easily produced from our textile electrodes. This study offers a new direction for optimizing micro-structures and electrochemical properties of flexible electrodes in wearable energy storage devices.

© 2017 Elsevier Ltd Rechargeable zinc ion battery is considered as one of the most potential energy storage devices for large-scale energy storage system due to its safety, low-cost, high capacity and nontoxicity. However, only a few cathode materials have been studied for rechargeable zinc ion batteries. Here, we firstly report manganese sesquioxide (Mn2O3) with Mn(III) state as cathode material for rechargeable zinc ion battery. The α-Mn2O3 cathode displays a reversible capacity of 148 mAh g−1, which is relatively high among all the reported cathode materials for ZIB. The cathode also exhibits good rate capability and excellent cycling stability with a long cycle life up to 2000 times. The ion storage mechanism of α-Mn2O3 in zinc ion battery was also revealed. The pristine α-Mn2O3 undergoes a reversible phase transition from bixbyite structure to layered-type zinc birnessite during the electrochemical zinc ion insertion and extraction. The results not only benefit for the practical application of rechargeable zinc ion battery, but also broaden the horizons of understanding the electrochemical behavior and mechanism of rechargeable zinc ion batteries.

With the fast development of portable and wearable devices, flexible supercapacitor electrodes are widely researched. Here, comprehensive approaches were designed to introduce carbon nanotube (CNT) and/or MnO2 into activated carbon fiber felt (ACFF) using “dipping and drying” method. Differences on micro-morphologies and electrochemical characteristics for prepared textiles were compared. High-performance flexible MnO2/CNT/ACFF composite electrodes were synthesized by introducing CNT and MnO2/CNT fillers successively. Compared with original ACFF textiles, significant improvements in electrochemical performance were achieved. Areal capacitance, energy density and power density of the composite textiles reached as high as 4148 mF cm−2, 141 μWh cm−2 and 4466 μW cm−2, respectively. Furthermore, flexible supercapacitors were fabricated based on the composite textile electrodes and gel electrolytes. When being bent at different angles or suffering deformations such as bending for 100 cycles, the flexible supercapacitors preserve almost all the capacitance, which indicates the excellent flexibility of the composite textile electrode. This work provides various approaches to design composite textiles, and the prepared MnO2/CNT/ACFF composite textile may be a promising electrode material for high-performance flexible supercapacitors.

Developing high-performance flexible film-like electrodes is still a primary task for the practical applications of wearable/portable planar supercapacitors. In this work, a facile and effective approach, i.e., stacking up layers of polyaniline (PANI)/carbon nanotube (CNT) composite networks inside air-laid papers, is proposed to fabricate highly flexible paper electrodes with large areal capacitance and superior rate capability. The layer-by-layer deposition of PANI/CNT networks endows the fabricated paper electrodes with high loading and uniform distribution of PANI; meanwhile, the good electrical conductivity and porous structure of these introduced PANI/CNT networks guarantee sufficient paths for electron movement and ion transportation in the electrodes. Consequently, when 4 layers of PANI/CNT networks (with optimal PANI content) are stacked inside papers, the areal capacitance of the prepared electrode is as high as 1506 mF cm−2 at a charge/discharge current of 10 mA cm−2 and 1298 mF cm−2 at 100 mA cm−2; the electrode also exhibits high flexibility and good cycling stability (with 82% capacitance retention after 11 500 charge/discharge cycles). These merits make our PANI/CNT/papers promising candidates for flexible planar supercapacitor electrodes. Besides, this work is believed to provide a new thought for producing high-loading and high-energy wearable/portable energy storage devices.

Using ab initio calculations, we systematically investigate graphene nucleation on 10 representative metal substrates that have been used in graphene growth by chemical vapor deposition. We find that the metal substrates can be divided into three categories with respect to the competition between carbon–carbon (C–C) and carbon–metal (C–M) interactions, which leads to the distinct critical size (Nc) dependence of the smallest graphene precursor on the substrates. The C–M interactions are weak on Ag, Au, Cu, and Co substrates, and the chemical potential of carbon decreases monotonically to approach that of graphene as the size of the carbon clusters increases. We observed an Nc around C13–C14 corresponding to the structural transition from a linear chain to sp2 configuration on these substrates. In contrast, the C–M interactions are strong on Ru, Pt, Rh, and Ir substrates, and the extremely stable carbon monomer thermodynamically determines the larger Nc about C19. The third category is Ni and Pd substrates...

Graphene/MnO2 composites are introduced into activated carbon fiber felt (ACFF) to fabricate composite textile electrodes. Their micro-structure, electrical properties and electrochemical performance for supercapacitor applications in different neutral electrolytes (1 M NaNO3 and Ca(NO3)2 aqueous solutions) have been studied. The composite electrodes have similar pore features to original ACFF textiles, but show notably enhanced electrical and electrochemical performance. The composite textile electrodes show low electrical resistance, high specific capacitance (up to 1516 mF cm−2 in neutral electrolytes) and excellent cycling stability (no capacitance decay after 5000 charge–discharge cycles). Besides, electrochemical capacitance of composite textile electrodes in Ca(NO3)2 electrolyte is higher than that in NaNO3 electrolyte at low scan rates (1–5 mV s−1), but the situation is reversed when scan rates are higher than 10 mV s−1. Above all, the results show that our low-cost composite textile electrodes are high-performance in neutral electrolytes, which is helpful for developing large-scale energy storage devices.

The merits of zinc metal anodes such as high chemical stability, low cost and ultrahigh volumetric capacity endow Zn based batteries/hybrid capacitors with great potential applications for electronic products. However, unstable stripping/plating of zinc anodes tends to cause the formation of protuberances/dendrites and side reactions such as water decomposition on anode surfaces, eventually leading to the failure of Zn based electrochemical energy storage devices. Herein, we report the fabrication of free-standing, highly flexible and conductive carbon nanotube (CNT)/paper scaffolds to stabilize zinc metal anodes. The free-standing CNT scaffolds only need to be placed between zinc anodes and separators when assembling zinc anode-based batteries/hybrid capacitors. On the surface of the zinc electrode, the scaffolds’ porous skeleton mechanically regulates Zn2+ deposition sites and their conductive CNT networks maintain a stable electric field during Zn stripping/plating processes, thus retarding the formation of protuberances/dendrites and the occurrence of side reactions. The scaffold-stabilized zinc anodes displayed small polarization voltages, a long cycling life over 1800 h and superior capability for fast charging-discharging. In addition, benefiting from the high electrochemical stability and reversibility of the scaffold-stabilized zinc anodes, zinc-ion batteries/hybrid capacitors with ultralong cycle lives were successfully constructed. This work provides a scalable approach to stabilize zinc metal anodes for long-life zinc-ion batteries and zinc-ion hybrid capacitors.

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim A facile preparation method was proposed to fabricate core-sheath structured elastic cord/carbon nanotube (CNT)/polyaniline (PANI) composite fibers with excellent electrochemical performance and good mechanical stretchability. Specifically, we developed a “surface melting for stable attachment” strategy to combine CNT/PANI composite film tightly with elastic cord fiber. The fabricated fiber-like elastic cord/CNT/PANI composite electrode displays a large gravimetric capacitance of 394 F g−1(corresponds to a linear specific capacitance of 15.4 mF cm−1) and superior rate capability. The electrode capacitance has no obvious decrease when the electrode was stretched from original state to a large stretch ratio of 100%, and the capacitance maintains 98% after 100 stretch-release cycles; besides, the electrode at stretching state possesses almost same cycling stability and rate capability as it at original state. These results indicate robust micro-structure and outstanding stretchability of our fiber-like elastic cord/CNT/PANI composite electrode. Consequently, all-solid-state supercapacitors assembled based on the fiber-like electrode also exhibit impressive stretchability. Overall, the proposed facile method for producing stretchable fiber-like electrodes/supercapacitors is believed to further boost the practical application of stretchable and wearable energy storage devices.

Carbon nanotube (CNT) aerogels with controlled hierarchical microstructures and versatile performance were prepared by a freeze-drying method under the facile freezing temperature of −20 °C. The as-prepared CNT aerogels were composed of CNT/binder (sodium carboxymethylcellulose, CMC) hybrid sheet structures, whose morphologies could be controlled by changing the weight ratio of CMC solution to CNT paste. The aerogels displayed a very low density of 32.7–77.7 mg/cm3, fairly high mechanical strength, good machinability, an outstanding electrical conductivity of 0.034–0.162 S/cm, and an ultralow thermal diffusivity of 2.09–4.54 mm2/s. In addition, we proposed formulas to describe the relationships between volume density of the fabricated aerogels and solid content or carbon content in CNT slurries.

High-performance compressible supercapacitors were realized based on functionally synergic multiscale carbon composite textiles. The composite textiles were fabricated by introducing nanoscale carbon fillers, i.e., carbon nanotube (CNT) or graphene (GN), on activated carbon fiber felt (ACFF) body material using a “simple impregnation and freeze-drying method”. The prepared CNT/ACFF and GN/ACFF composite textiles preserved the advantages of the ACFF body material in structure, such as being foldable and windable, whereas functionally they showed a synergic effect of the body material and nano-fillers, by integrating the excellent electrical conductivity of the nano-fillers with the high specific surface area and appropriate pore structures of ACFF. Thus, their electrochemical performances were significantly enhanced in the assembled symmetric supercapacitors, compared with those of the existing studies on textile electrodes. Areal capacitance, energy density and power density could be as high as 3350 mF cm−2, 112 μW h cm−2 and 4155 μW h cm−2, respectively. Most interestingly, our composite textiles can be compressed into a much smaller-sized and windable supercapacitive device, providing opportunities for their application as portable textile supercapacitors.

Rechargeable zinc ion battery is considered as a very promising energy storage system due to its high safety, low cost, and environmentally friendliness. Vanadium oxides with high capacity, good rate performance, and excellent cycle life are important cathode materials for zinc ion batteries. Herein, V10O24.12H2O(VOH) with large interlayer spacing and high valence state is prepared by a facile hydrothermal method and used as the cathode material in zinc ion battery. The Zn/VOH battery delivers a capacity of 327 mAh g−1 at 0.1 A g−1, and exhibit excellent cycling performance with high retention capacity (115 mAh g−1) after 3000 cycles at 1 A g−1. Zinc ion and proton insertion mechanism is proposed by exploring the evolutions of the phase and morphology. Zinc ion and proton insertion mechanism is verified by different zinc salt electrolytes. The reaction kinetics tests of Zn/VOH (galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS)) indicate that the zinc ion insertion process has fast reaction kinetics and the proton insertion process slows down the reaction kinetics. The research of Zn/VOH system expand the cathode material of zinc ion battery and enrich the comprehension of zinc ion battery reaction mechanism.

Enhancement of thermal conductivity of natural flake graphite/polymer (NFG/polymer) composite sheets, prepared with tape casting method, was studied by adding carbon-based nano-fillers including carbon black, carbon nanotube (CNT) and graphene. The in-plane thermal conductivities of the composites, i.e., the thermal conductivities along the tape casting plane, were measured. The improvement of thermal conductivities of the composites was observed to be up to 24% by adding CNT and 31% by adding graphene at 10 wt.%. Micro-structures of the NFG/polymer composites were revealed by X-ray diffraction patterns and field emission scanning electron microscopy images to delineate the mechanism of thermal conductance in the composites. From the observed structure, a new thermal conductivity model for the composites with CNT and graphene additives was constructed based on a bridging mechanism. The new model applies well to the measured thermal conductivities of the as-prepared samples. It is expected that the model could also be applied well to composites added with other homologous materials for bridging thermal contacts.

Breathable and wearable energy storage is achieved based on an innovative design solution. Carbon nanotube/MnO2 -decorated air-laid paper electrodes, with outstanding flexibility and good electrochemical performances, are prepared. They are then assembled into solid-state supercapacitors. By making through-holes on the supercapacitors, breathable and flexible supercapacitors are successfully fabricated.

Formation and conversion mechanisms between single-crystal gamma-MnOOH and manganese oxides had investigated systematically. Without extra surfactant or template, α-MnO2 nanorods and prismatic single crystalline γ-MnOOH rods had been synthesized under hydrothermal treatment in this study. The formation and conversion mechanisms of prismatic γ-MnOOH rod were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that the formation process includes three evolution stages: (1) formation of α-MnO2 nanorods whiskers; (2) transformation from α-MnO2 nanorods to prismatic γ-MnOOH rods by a dissolution-growth-recrystallization process; and (3) preferred growth on ( 1 1 1 ¯ ) crystal plane. In addition, β-MnO2, Mn2O3 or Mn3O4 rods could be obtained by calcination of the γ-MnOOH rods at different temperatures, which indicated that γ-MnOOH is an important precursor for preparing manganese oxides. The morphology and dimension of γ-MnOOH rods remained unchanged after converted to β-MnO2, Mn2O3 and Mn3O4.

Nanocrystalline LiFePO4 and LiFe0.97Sn0.03PO4 cathode materials were synthesized by an inorganic-based sol–gel route. The physicochemical properties of samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and elemental mapping. The doping effect of Sn on the electrochemical performance of LiFePO4 cathode material was extensively investigated. The results showed that the doping of tin was beneficial to refine the particle size, increase the electrical conductivity, and facilitate the lithium-ion diffusion, which contributed to the improvement of the electrochemical properties of LiFePO4, especially the high-rate charge/discharge performance. At the low discharge rate of 0.5 C, the LiFe0.97Sn0.03PO4 sample delivered a specific capacity of 158 mAh g−1, as compared with 147 mAh g−1 of the pristine LiFePO4. At higher C-rate, the doping sample exhibited more excellent discharge performance. LiFe0.97Sn0.03PO4 delivered specific capacity of 146 and 128 mAh g−1 at 5 C and 10 C, respectively, in comparison with 119 and 107 mAh g−1 for LiFePO4. Moreover, the doping of Sn did not influence the cycle capability, even at 10 C.

The increasing worldwide interest in MnO2for supercapacitor applications is based on anticipation that MnO2-based high-voltage aqueous supercapacitors will ultimately serve as a safe and low-cost alternative to state-of-the-art commercial organic-based electrochemical double-layer capacitors or RuO2-based acid systems. In this paper, the physicochemical features, synthesis methods, and charge storage mechanism of MnO2as well as the current status of MnO2-based supercapacitors are summarized and discussed in detail. The future opportunities and challenges related to MnO2-based supercapacitors have also been proposed.

High-performance flexible textile electrodes and fiber electrodes are produced simultaneously by a newly proposed effective strategy. Activated carbon fiber cloth (ACFC)/carbon nanotubes (CNTs) and ACFC/MnO2/CNTs composites are designed as high-performance flexible textile electrodes. Theses textiles can also be easily dismantled into individual fiber bundles used as high-performance flexible fiber electrodes.

Poly(ethylene oxide) (PEO) nanofibers were prepared by electrospinning PEO solution with a mixed solvent of ethanol and deionized water. The results show that the mixed solvent system has noteworthy influences on structures and properties of electrospun PEO nanofibers, including molecular chain orientation, crystallinity degree, surface morphology, fiber diameter, diameter distribution, spinnability, and productivity. With increasing ethanol content in the mixed solvent, wrinkly morphologies appear on the surface of PEO nanofibers due to a high evaporation rate of ethanol during electrospinning process. The dielectric constant, dipole moment, conductivity, density, boiling point, and solubility parameter of the mixed solvent become lower with the ethanol content increasing. Besides, the hydrogen-bonding interactions between PEO and solvents become weaker. As a result, PEO nanofibers with larger diameters, lower molecular chain orientation, and crystallinity degree are obtained. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 135, 45787.

Flexible asymmetric supercapacitors with excellent electrochemical performance and aesthetic property are realized by using ultrathin two-dimensional (2D) MnO2 and graphene nanosheets as cathode and anode materials, respectively. 2D MnO2 nanosheets (MSs) with a thickness of ca. 2 nm are synthesized with a soft template method for the first time, which achieve a high specific capacitance of 774 F g−1 even after 10000 cycles. Asymmetric supercapacitors based on ultrathin MSs and graphene exhibit a very high energy density up to 97.2 Wh kg−1 with no more than 3% capacitance loss after 10000 cycles in aqueous electrolyte. Most interestingly, we show that the energy storage device can have an aesthetic property. For instance, a “Chinese panda” supercapacitor is capable of lighting up a red light emitting diode. This work has another, quite different aspect that a supercapacitor is no longer a cold industry product, but could have the meaning of art.

Wireless LAN is a heterogeneous wireless network, the main broadband access networks, has been widely used in people's daily life. In this paper, based on wireless local area network for heterogeneous wireless networks, a class of attack scenario, a forward with a directional, remote control and a fake AP to conduct security protocol analysis, active attacks on the control platform design.

To meet the rapidly growing demand, it is necessary to develop novel flexible energy storage devices with a high energy density in a limited area, a fast charging ability, a low cost for mass production and a miniaturized device size. To address the above issues, here we introduce the co-electro-deposition strategy, which is able to prepare an electrode material with a high areal capacitance (1670 mF cm−2 at 0.5 mA cm−2), a high areal mass (8.5 mg cm−2), an excellent mechanical robustness, a high through-put and great convenience even on a piece of a ubiquitous stainless steel mesh current collector. Based on this advancement, we are able to obtain an ultrathin (less than 200 μm) aqueous asymmetric supercapacitor device with a high energy density (1.8 × 10−3 W h cm−3), a high power density (0.38 W cm−3 at 3.62 × 10−4 W h cm−3) and an excellent rate capability. This energy storage device is integrated into a prototype smart card to drive a light emitting diode (LED) indicator, which is charged for 5 seconds and can light up the indicator for more than 2 hours, demonstrating great promise in miniaturized novel flexible energy storage devices.

Manganese dioxide exhibits the ideal capacitive behavior in aqueous electrolytes containing alkaline-earth cations (Mg 2+ , Ca 2+ , or Ba 2+ ). A specific capacitance value as high as 325 F g -1 was obtained in 0.1 mol L -1 Mg(NO 3 ) 2 electrolyte at 2 mV s -1 . The ideal capacitive behavior, high specific capacitance, good coulombic efficiency, and rate ability of manganese dioxides in aqueous electrolytes containing bivalent cations (Mg 2+ , Ca 2+ , or Ba 2+ ) indicate that these alkaline-earth cations might be good alternatives for the state-of-the-art univalent alkaline cations. Moreover, activated carbon/MnO 2 asymmetric capacitors with 2 V operating voltage were built up based on the aqueous electrolytes containing these alkaline-earth cations. The energy density of the AC/MnO 2 asymmetric capacitor with Ca 2+ cation at a current density of 0.3 A g -1 was found to be 21 Wh Kg -1 .