Magnetic tubular carbon nanofibers as anode electrodes for high‐performance lithium‐ion batteries

Novel magnetic tubular carbon nanofibers (MTCFs) are prepared through the combination technique of hypercrosslinking, control extraction, and carbonization. The diameter of MTCFs is mainly concentrated between 90 and 120 nm, and the average tube diameter is about 30 nm. A trace amount of Fe₃O₄ exists inside the MTCFs with a particle size of 3 nm, which is formed by in situ conversion of the catalyst (FeCl₃) for the hypercrosslinking reaction. The MTCFs with high surface area (448.74 m² g^?1) and porous wall are used as anode material for lithium‐ion batteries. The electrochemical properties of MTCFs are compared, and tubular carbon nanofibers (TCFs) prepared by the complete extraction. Electrochemical analysis shows that the introduction of Fe₃O₄ nanoparticles makes MTCFs have higher reversible capacity and better rate performance. MTCFs exhibit high reversible specific capacity of 1011.7 mAh g^?1 after 150 cycles at current density of 100 mA g^?1. Even at high current density of 3000 mA g^?1, a remarkable reversible capacity of 270.0 mAh g^?1 is still delivered. Thus, the novel MTCFs show potential application value in anode material for high‐performance lithium‐ion battery.     

One‐pot synthesis of composite NiO/graphitic carbon flakes with contact glow discharge electrolysis for electrochemical supercapacitors

Thanks to their high power density and degree of reversibility, supercapacitors are electrochemical devices that narrow the gap between secondary batteries and traditional dielectric capacitors in the traditional Ragone plot. However, their use is still hindered by their capability to achieve higher energy density. In this work, we present a one‐pot synthesis procedure of composite graphitic carbon flake‐supported NiO for electrochemical energy storage application. We used cathodic contact glow discharge electrolysis by applying 120 Vdc terminal voltage between a thin Pt wire, slightly submerged in an aqueous solution of NiSO₄(H₂O)₆ + Na₂SO₄, and a large surface area carbon graphite anode. Strong active species generated within the micro‐plasma volume locally reduce the nickel precursors to form NiO materials, while at the anodically polarized graphite rod, the forces holding the graphene layers together are weakened by ion/solvent intercalation producing micrometer‐sized graphitic carbon flakes. The morphological characterization is carried out by electron microscopy, energy dispersive X‐ray spectroscopy, powder X‐ray diffraction, and micro‐Raman spectroscopy. Cyclic voltammetry, constant‐current charge/discharge, and electrochemical impedance spectroscopy in 5 mol l^?1 KOH solution are carried out to evaluate the electrochemical energy storage performance of the material. We show that carbon flake‐supported NiO exhibits the dual combination of electric double‐layer capacitance with faradic behavior, giving 495 F g^?1 specific capacitance at 2 A g^?1 current density. Copyright © 2015 John Wiley & Sons, Ltd.     

Porphyrin-based conjugated microporous polymers with dual active sites as anode materials for lithium-organic batteries

Conjugated microporous polymers have been regarded as ideal electrode materials for green lithium-ion batteries (LIBs) considering their advantages such as insolubility, adjustable structure and porosity. Herein, we synthesize porphyrin-based CMPs (Co-PCMPs) with dual active sites composed of metal-N4 conjugated macrocycle and conjugated carbonyl groups through the condensation polymerization. In view of the rational design and unique organic skeleton, when used as the anode material for LIBs, Co-PCMPs show a high capacity (700 mAh g^?1 at 0.05 A g^?1) and excellent rate capability (400 mAh g^?1 at 1.0 A g^?1). Meanwhile, theoretical calculations are used to further study the lithium storage mechanism of Co-PCMPs as the anode material for LIBs. In addition, a full cell is also assembled by using LiCoO₂ as the cathode material and Co-PCMPs as the anode material, which also shows a high capacity (212 mAh g^?1 at 0.05 A g^?1) and good rate capability (116 mAh g^?1 at 0.2 A g^?1), implying the possibility of practical applications of this type of conjugated microporous polymers.     

Composite of manganese dioxide impregnated in porous hollow carbon spheres for flexible asymmetric solid‐state supercapacitors

Compared with symmetric supercapacitors, asymmetric supercapacitors are been widely applied in energy storage devices because of delivering an impressible energy density. Herein, a simple temple strategy was used to fabricate the porous hollow carbon spheres (PHCS) with high specific surface area of 793 m² g^?1, large pore volume of 1.0 cm³ g^?1 and pore size distribution from micropores to mesopores, serving as the capacitive electrodes of asymmetric supercapacitors. Subsequently, manganese dioxide (MnO₂) was impregnated into the PHCS to form a faradic electrode with a promising performance, owing to a synergistic effect between high capacity MnO₂ and conductive PHCS. Furthermore, the flexible asymmetric solid‐state devices were constructed with PHCS anode, PHCS@MnO₂ cathode, and PVA/LiCl electrolyte, extending a voltage window up to 1.8 V. The extensive voltage window would lead to an increased energy density. In our case, the flexible asymmetric sandwich exhibit excellent electrochemical performance in terms of a high energy density capacity of 26.5 W·h kg^?1 (900 W kg^?1) and superior cycling performance (10 000 cycles). Therefore, the developed strategy provides a strategy to achieve the PHCS‐based composites for the application in the asymmetric solid‐state supercapacitors, which will enable a widely field of flexible energy storage devices.     

A novel high specific capacity lithium‐ion capacitor battery with Li+‐doped Ni0.64Al0.64Mn0.56O2 prepared by coprecipitation method as cathode active material

Lithium‐ion capacitor battery is a late‐model energy storage system. It can combine the lithium‐ion battery with the capacitor to ensure that it has a high specific capacity and excellent large‐current discharge performance. In this paper, a novel Li⁺‐doped Ni_0.64Mn_0.64Al_0.56O₂ is synthesized by coprecipitation method and as a capacitor active material with commercialized LiNi_1/3Co_1/3Mn_1/3O₂ in different proportions forms the cathode of the lithium‐ion capacitor batteries. By analyzing the results of physical property characterization, when the mass ratio is 7:3, the crystal size of cathode material is less than 2 μm with uniform porous distribution. And, through electrochemical tests, the cathode has the greatest excellent reversibility, the lowest‐charge resistance, and the fastest‐lithium‐ion diffusion rate. Specific capacity can reach 196.34 mAh g^?1 at 0.5°C and, even at 5°C current density, it also can be 67.63 mAh g^‐1. After 110 times charge and discharge cycles, capacity retention of this cathode material at 5°C still can be over 85%.     

In situ self‐template synthesis of cobalt/nitrogen‐doped nanocarbons with controllable shapes for oxygen reduction reaction and supercapacitors

Shape‐controlled Co/N‐doped nanocarbons derived from polyacrylonitrile (PAN) were synthesized by a one‐step in situ self‐template method followed by a pyrolysis procedure. This is the first study to tune the nanostructure of Co/N‐doped carbon materials by providing a metal salt as the template and additive. The moderate surface area (699.47 m² g^?1), highly developed pore structure, homogenous Co and N doping and designed “egg‐box” structure impart Co/N‐doped cross‐linked porous carbon (Co/N‐CLPC) with excellent electrocatalytic activity and capacitive performance. This material displayed an onset potential of 0.805 V (vs RHE), a current density of ?5.102 mA cm^?2, excellent long‐term durability, and good resistance to methanol crossover, which are comparable with the characteristics of a commercial 20‐wt% Pt/C catalyst. In addition, Co/N‐CLPC demonstrated a high specific capacitance of 313 F g^?1 at 0.5 A g^?1, notable rate performance of 63% at 50 A g^?1, and good cycling stability of 104.8% retention after 5000 cycles when used as a supercapacitor electrode. This method enables new routes to obtaining Co/N‐doped nanocarbons with shape‐controlled structures for energy conversion and storage applications.     

Lignin‐derived heteroatom‐doped porous carbons for supercapacitor and CO2 capture applications

The present study reports the economic and sustainable syntheses of functional porous carbons for supercapacitor and CO₂ capture applications. Lignin, a byproduct of pulp and paper industry, was successfully converted into a series of heteroatom‐doped porous carbons (LHPCs) through a hydrothermal carbonization followed by a chemical activating treatment. The prepared carbons include in the range of 2.5 to 5.6 wt% nitrogen and 54 wt% oxygen in its structure. All the prepared carbons exhibit micro‐ and mesoporous structures with a high surface area in the range of 1788 to 2957 m² g^?1. As‐prepared LHPCs as an active electrode material and CO₂ adsorbents were investigated for supercapacitor and CO₂ capture applications. Lignin‐derived heteroatom‐doped porous carbon 850 shows an outstanding gravimetric specific capacitance of 372 F g^?1 and excellent cyclic stability over 30,000 cycles in 1 M KOH. Lignin‐derived heteroatom‐doped porous carbon 700 displays a remarkable CO₂ capture capacity of up to 4.8 mmol g^?1 (1 bar and 298 K). This study illustrates the effective transformation of a sustainable waste product into a highly functional carbon material for energy storage and CO₂ separation applications.     

Enhanced hetero‐elements doping content in biomass waste‐derived carbon for high performance supercapacitor

Betel nut wastes are firstly modified with nitric acid/thiourea to fabricate hetero‐element doping carbon (C‐H‐T) for energy storage. C‐H‐T exhibits improved content of O (12.27%), N (2.52%), and S (2.88%) compared with that of purely carbonized carbon with O (9.2%) and N (1.76%). Without nitric acid heat treatment, the carbon materials prepared by hydrothermal treatment with thiourea only get increasing hetero‐elements content of O (10.46%), N (2.9%), and S (0.53%). The similar results have been obtained using urea and melamine as dopants. Due to the synergistic effects of the hetero‐elements containing functional groups, C‐H‐T get a significant enhancement in its electrochemical properties with a high capacitance (423 F g^?1 at 0.5 A g^?1) in KOH electrolyte. C‐H‐T based coin‐type symmetric supercapacitors display maximum energy density of 61.7 Wh kg^?1 and considerate cycling ability with 94% capacitance retention after 10 000 cycles. The fabricated two‐step method can inspire the increase of hetero‐elements content in carbon materials to develop its application in energy storage.     

Enhanced pseudocapacitive energy storage properties of Nb2O5/C core‐shell structures with the surface modification

Pseudocapacitive energy storage is an attractive technology as it can achieve high energy density at high rate conditions. However, its practical application has been an issue because of low electrical conductivity of nanoscale electrode materials. Surface coating is an effective way to enhance the electrochemical properties of the electrochemical energy storage system by helping electron transfer between the electrode material and current collector. In order for surface coating technologies to be applied to pseudocapacitive energy storage field, providing fast ions and electrolyte transport through the coating layer as well as high electrical conductivity is essential because pseudocapacitors aim for high rate charge/discharge capability. In this paper, the Nb₂O₅/carbon core‐shell structure is developed to meet these requirements. Simple microwave‐assisted method is applied to create nanoscale (approximately 5 nm) conductive carbon layer on the surface of bare Nb₂O₅ nanoparticles, and the high power capability of Nb₂O₅/carbon core‐shell is improved further by oxidation process providing open structure for electrolyte and ion diffusion. Thick electrode architecture containing oxidized Nb₂O₅/carbon core‐shell shows superior high rate performance as capacities of 215 C g^?1 are obtained at a 50 mV s^?1 scan rate.     

TiO2 nanoparticle embedded nitrogen doped electrospun helical carbon nanofiber-carbon nanotube hybrid anode for lithium-ion batteries

TiO₂ nanoparticles decorated nitrogen (N) doped helical carbon nanofiber (CNF)-carbon nanotube (CNT) hybrid material is prepared by low-cost electrospinning technique followed by hydrothermal method. Morphological investigations establish helical structure of CNFs with hierarchical growth of CNTs around CNFs. The hybrid material shows a high specific surface area of 295.17 m² g^?1 with nanoporous structure. X-ray photoelectron spectroscopic studies establish Ti–O–C/Ti–C bond mediated charge transfer channel between TiO₂ nanoparticles and carbon structures with the success of N doping in CNFs. The electrospun hybrid material delivered high reversible charge capacities of 316 mAh g^?1 (100th cycle) and 244 mAh g^?1 (100th cycle) at a current density of 75 mA g^?1 and 186 mA g^?1 respectively. The charge capacities obtained for different applied current densities are higher than the conventional graphitic microporous microbeads anode. Results indicate that the hybrid material reported here shows high performance compare to graphite for LIBs.     

Metal-organic frameworks supported Ni–Co–S nanosheet arrays for advanced hybrid supercapacitors

Constructing self-supporting porous electrode material with abundant electrochemical active sites can effectively improve the energy storage capacity of supercapacitors. Herein, a novel electrode material (NCS@Co-ZIF/NF) is developed by depositing zeolitic imidazolate frameworks (Co-ZIF) on nickel foams (NF), which is adopted as a precursor (Co-ZIF/NF) to electrodeposit nickel-cobalt sulfides (NCS). The nanosheet arrays with cross-porous structures provide NCS@Co-ZIF/NF with excellent electrochemical characteristics, including a high specific capacity of 144.4 mAh g^?1 at the current density of 1 mA cm^?2, 60.5% capacity retention at 50 mA cm^?2, and superb long-term cycle stability. Furthermore, NCS@Co-ZIF/NF//AC hybrid supercapacitor is fabricated by using NCS@Co-ZIF/NF as positive electrodes and activated carbon (AC) as negative electrodes, which exhibits a high energy density of 33.9 Wh kg^?1 at a power density of 145 W kg^?1.     

Cobalt oxide nanosheets anchored onto nitrogen‐doped carbon nanotubes as dual purpose electrodes for lithium‐ion batteries and oxygen evolution reaction

Transition metal oxides (TMOs) have been extensively explored as promising electrode materials for electrochemical energy storage and catalysis. However, TMOs intrinsically have low electronic conductivity and suffer severe volume change during electrochemical cycling. In this study, we develop an effective strategy to enhance conductivity and buffer volume changes of TMOs, in which networked nitrogen‐doped carbon nanotubes (N‐CNTs) are incorporated into Co₃O₄ nanosheets system. Based on the whole mass of Co₃O₄ and N‐CNT, the composites can maintain a stable discharge capacity of ~590 mAh g^?1 after 80 cycles at a current density of 0.5 A g^?1. Moreover, the composites also exhibit greatly enhanced catalysis ability towards oxygen evolution reaction (OER), ie, small Tafel slope of 84 mV dec^?1, low overpotential of 310 mV at a current density of 10 mA cm^?2, and almost no activity decay throughout 30‐hour continuous operation. This study lays a new route for smartly designing advanced electrode materials for energy storage and electrochemical catalysis.     

Synergistic effect of sulfur on electrochemical performances of carbon‐coated vanadium pentoxide cathode materials with polyvinyl alcohol as carbon source for lithium‐ion batteries

Vanadium pentoxide (V₂O₅) is a common cathode material for lithium‐ion battery, but its low electronic and ionic conductivity seriously affect its electrochemical performances. In this paper, a type of carbon‐coated V₂O₅ and S composite cathode material with PVA as the carbon source is utilized to lithium‐ion batteries. X‐ray diffraction and Raman test results illustrate that sulfur can make the V₂O₅ lose part of oxygen atoms and become nonstoichiometric vanadium oxide (V₂O_5‐x). Electrochemical test results show that sulfur can provide a considerable proportion of the specific capacity of the whole cathode. This illustrates that the synergistic effect of sulfur can optimize the structure of vanadium pentoxide in order to increase more electron transfer channels, and at the same time, it also can provide additional specific capacity for the whole cathode. When the ratio of V₂O₅ and sulfur is 1:3, the discharge specific capacity can reach 923.02, 688.37, and 592.70 mAh g^?1 at 80, 160, and 320‐mA g^?1 current density, respectively, and after 100 times charge and discharge cycles at 320‐mA g^?1 current density, the capacity retention rate can achieve to more than 60%.     

Graphene‐wrapped poly(2,5‐dihydroxy‐1,4‐benzoquinone‐3,6‐methylene) nanoflowers as low‐cost and high‐performance cathode materials for sodium‐ion batteries

Graphene‐wrapped poly 2,5‐dihydroxy‐1,4‐benzoquinone‐3,6‐methylene (PDBM) nanocomposites with three‐dimensional nanoflower structures have been successfully prepared through the ultrasonic exfoliation and reassembly process in methanol. Compact distribution of graphene into the nanocomposite has established a three‐dimensional conductive network, which contributes to improved properties on discharge capacity and cycle performance. Composite with 20 wt% graphene was proved the best ratio when used in sodium‐ion batteries. Its initial discharge capacity can achieve 210 at 30 mA g^?1. After 100 cycles, the capacity is stable at 121 mAh g^?1. The composite featuring highly conductive channels and multidimensional electron transport pathway is synthesized by an easy ultrasonic way, which may be applied in large scales for sodium‐ion batteries.     

Li–Na metal compounds inserted into porous natural wood as a bifunctional hybrid applied in supercapacitors and electrocatalysis

As a green and sustainable natural resource, wood is regarded as a feasible candidate material for developing green and sustainable energy due to its natural porous structure. However, the conductivity of wood is poor, which restricts its application in energy storage. In this research, a novel material with Li–Na metal compounds inserted into porous carbonized lignin free wood (PCLFW) as a bifunctional hybrid is synthesized. This material with a high specific capacitance, high power density and excellent electrocatalytic activity is synthesized. The final product shows a high specific capacitance of 255 F g^?1, high energy density of 31.88 Wh kg^?1 and power density of 3188 W kg^?1. Moreover, after experiencing 5000 cycles, the specific capacitance is maintained at 239 F g^?1 (capacitance retention of 93%). In addition, the hybrid exhibits excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities in alkaline solution, with overpotentials of 349 mV (Tafel = 192 mV dec^?1) and 484 mV (Tafel = 184 mV dec^?1), respectively. Meanwhile, the hybrid also shows a larger initial and half-wave potentials of ?0.12 V and ?0.22 V, reflecting an outstanding oxidation-reduction reaction (ORR) property. In a word, this work provides a new idea for us to fabricate wood-based hybrid for high-performance energy storage devices and carbon-based catalysts.     

Cooperation of Fe2O3@C and Co3O4/C subunits enhances the cyclic stability of Fe2O3@C/Co3O4 electrodes for lithium‐ion batteries

A Fe₂O₃@C/Co₃O₄ hybrid composite anode is synthesized via a two‐step hydrothermal method in which the acetylene carbon black component serves as a conductive matrix and as an effective elastic buffer to relieve the stress from Fe₂O₃@C and Co₃O₄/C during the electrochemical testing. The crystallinity, structure, morphology, and electrochemical performance of the composites are systematically characterized. Galvanostatic charge/discharge measurements of Fe₂O₃@C/Co₃O₄ present the excellent rate performance and cyclic stability. Its reversible capacity reaches 1478 mAh·g^?1 after 45 cycles, and it is equal to 1035 mAh·g^?1 after 350 cycles at a current density of 200 mA·g^?1. Furthermore, the changes after 30, 45, 60, 90, and 120 cycles are investigated. It is found that the electrochemical performance varies with the morphological change of the electrode surface. Correspondingly, the microstructure, cyclic voltammetry curves, and Nyquist plots significantly change as a consequence of cycling. The results of this study provide an understanding of the increased capacity and excellent cyclic performance of a new anodic material for Li‐ion batteries.     

Submicron‐sized Sb2O3 with hierarchical structure as high‐performance anodes for Na‐ion storage

Submicron‐sized Sb₂O₃ with hierarchical structure was successfully prepared via a synthesis of one‐step solvothermal chemical route. Na‐ion storage performance of Sb₂O₃ material was investigated. Sb₂O₃ anode exhibits a high reversible capacity (approximately 350 mAh/g) and stable cycle stability (greater than 95%) over 100 cycles at 100 or 200 mA/g. A full battery with Sb₂O₃ anode and P2‐Na_2/3Ni_1/3Mn_1/2Ti_1/6O₂ (PTO) cathode indicated a high energy density of 216.6 Wh/kg.     

Morphology‐dependent electrochemical performance of nitrogen‐doped carbon dots@polyaniline hybrids for supercapacitors

In this work, the binary N‐CDs@PANI hybrids were fabricated by introducing zero‐dimensional nitrogen‐doped carbon dots (N‐CDs) into reticulated PANI. Firstly, N‐CDs were prepared by one‐pot microwave method, and then, the N‐CDs were introduced into in situ oxidative polymerization of aniline (ANI) monomer. The N‐CDs with abundant functional groups and high electronic cloud density played a significant role in guiding the polyaniline‐ordered growth into intriguing morphologies. Moreover, morphology‐dependent electrochemical performances of N‐CDs@PANI hybrids were investigated and N‐CDs improve static interaction and enhance the special capacitances in the N‐CDs@PANI hybrids. Especially, the specific capacitance of PC4 hybrid can reach 785 F g^?1, which exceed that of pure PANI (274 F g^?1) at current density of 0.5 A g^?1 according to three‐electrode measurement. And the capacitance retention of the PC4 hybrid still keeps 70% after 2000 cycles of charge and discharge. The N‐CDs@PANI hybrids can have potential applications in electrode materials, supercapacitors, nonlinear optics, and microwave absorption.     

High efficiency TiO2/MWCNT based anode electrodes for Li‐ion batteries

Freestanding multiwalled carbon nanotube and titanium (IV) oxide anode paper was prepared by vacuum filtration of multiwall carbon nanotubes/TiO₂ hybrid material, which was synthesized by the radio frequency magnetron sputtering techniques. Field emission scanning electron microscopy images revealed that the carbon nanotubes (CNTs) form a three‐dimensional nanoporous network, in which ultrafine TiO₂ crystals that had crystallite sizes ranging between 7.14 nm and 12.21 nm were distributed homogenously over the surfaces of multiwalled CNT bundles. Electrochemical measurements demonstrated that the prepared powder by using 200 W radio frequency power had excellent cyclic retention, with the high specific capacity of 230 rnAh g^?l up to 50 cycles at a current density. Freestanding papers composed of multiwall carbon nanotubes could act as a flexible mechanical support for strain release offering an efficient electrically conducting channel ,whereas the TiO₂ provides the high capacity. The electrochemical response is maintained in the initial and further cycling process. Such capabilities demonstrate that this model hold great promise for applications requiring flexible and bendable Li‐ion batteries. Copyright © 2014 John Wiley & Sons, Ltd.     

Preparation of stearic acid/halloysite nanotube composite as form‐stable PCM for thermal energy storage

A novel form‐stable composite as phase change material (PCM) for thermal energy storage was prepared by absorbing stearic acid (SA) into halloysite nanotube (HNT). The composite PCM was characterized by TEM, FT‐IR and DSC analysis techniques. The composite can contain SA as high as 60 wt% and maintain its original shape perfectly without any SA leakage after subjected to 50 melt–freeze cycles. The melting temperature and latent heat of composite (SA/HNT: 60/40 wt%) were determined as 53.46°C and 93.97 J g^?1 by DSC. Graphite was added into the SA/HNT composite to improve thermal storage performance, and the melting time and freezing time of the composite were reduced by 65.3 and 63.9%, respectively. Because of its high adsorption capacity of SA, high heat storage capacity, good thermal stability, low cost and simple preparation method, the composite can be considered as cost‐effective latent heat storage material for practical application. Copyright © 2011 John Wiley & Sons, Ltd.