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The role of graphene for electrochemical energy storage

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Abstract

Since its first isolation in 2004, graphene has become one of the hottest topics in the field of materials science, and its highly appealing properties have led to a plethora of scientific papers. Among the many affected areas of materials science, this 'graphene fever' has influenced particularly the world of electrochemical energy-storage devices. Despite widespread enthusiasm, it is not yet clear whether graphene could really lead to progress in the field. Here we discuss the most recent applications of graphene — both as an active material and as an inactive component — from lithium-ion batteries and electrochemical capacitors to emerging technologies such as metal–air and magnesium-ion batteries. By critically analysing state-of-the-art technologies, we aim to address the benefits and issues of graphene-based materials, as well as outline the most promising results and applications so far.

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... As an anode material for commercial LIBs, graphitized carbon exhibits high volumetric specific capacity and excellent cycling stability. However, theoretical studies indicate that, due to the significant electrostatic interactions between sodium ions and graphene layers, the sodium-ion storage capacity of graphite as a negative electrode material is limited [34]. Perk et al. [35] discovered that during the intercalation process, solvated sodium ions can intercalate into the channel structure of graphite, forming a ternary graphite intercalation compound (t-GIC), thereby enabling reversible sodium storage within graphite. ...
... Graphene offers ample active sites for Na + adsorption, attributable to its distinctive planar structure, substantial specific surface area, and numerous surface defects. Typically, graphene serves as a supportive substrate for various active nanomaterials, and it not only provides physical support but also prevents the restacking of nanomaterials by diminishing van der Waals forces between layers, thus preserving the structural integrity of the composite material [34]. ...
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Sodium-ion batteries (SIBs) are considered one of the most promising candidate technologies for future large-scale energy storage systems due to their highly abundant sodium and advantages similar to lithium-ion batteries (LIBs). However, the successful commercialization of SIBs relies heavily on the development of high-performance anode materials. Carbon-based materials are considered the ideal choice for SIBs negative electrode because of their abundant resources, cost-effectiveness, environmental friendliness, and excellent electrochemical properties. In this paper, the research progress of carbon anode materials in SIBs is reviewed. The application status of different carbon anode materials and the storage mechanism of four types of sodium ions in the hard carbon structure are systematically introduced and discussed. From the aspects of heteroatom doping, pore structure design, and layer spacing adjustment, this paper introduces the latest research progress in improving the sodium storage performance of carbon-based anode materials and summarizes the strategies for enhancing this performance. Finally, the future development directions and challenges of high-performance carbon-based anode materials are discussed and prospected, providing a feasible reference scheme for the rapid development of SIBs.
... Graphene and carbon materials with mechanical strength, flexibility, and long-term stability keep electrodes protected during cycling. [3][4][5]. Bukhari et al have presented a review of carbon-based materials for use in supercapacitor electrodes [6]. Maqsood et al developed an innovative method to make largescale three-dimensional porous carbon nanosheets using tree bark, which showed a good capacitance density [7]. ...
... Several studies have shown that graphene oxide and activated carbon can be used as electrode material for supercapacitors [8,9]. In addition, factors such as the binder and solvent used in the electrode ink [10] or the electrolyte [3,11] can have a significant effect on the chemical performance of supercapacitors. The porosity, active specific surface, hydrophilicity, and surface energy of electrodes can be adjusted by forming different nanostructures on the surface [5,12]. ...
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... Graphene is one atom thick in layer of carbon, tightly bound in a hexagonal honeycomb lattice. The substantial π-electron conjugation in graphene results in fascinating electronic, thermal, magnetic, optical, mechanical, and chemical properties [1][2][3]. Because of outstanding properties, graphene finds prominent applications in the electronic devices such as supercapacitor [4]; battery [5]; solar cell [6] and sensors [7]. ...
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Graphene-based electrode materials exhibit a high specific capacitance and long charge-discharge cycling life, but the material cost remains high because of the complexity of the graphene manufacturing process. This study employed an electrochemical exfoliation method to prepare graphene in a simple and ecologically friendly procedure. According to research findings, the disordered multi-layer structure of graphene exhibited great purity, porosity, and graphitization. The graphene electrode material showed high electrochemical properties in a two-electrode supercapacitor system, with a specific capacitance of 168.2 F g-1 at a current density of 0.1 A g-1 and a specific capacitance retention of 94.5 % after 1000 cycles. Research shows enormous potential of electrochemical approaches for producing large-scale graphene materials for energy storage application.
... Among nanostructured carbonaceous substances, graphene (Gr), is another desirable material for electrochemical energy applications [85]. Due to its single-atom thick, hexagonal sp 2 carbon matrix and a unique two-dimensional layered structure, graphene exhibits extraordinary physicochemical properties including excellent conductivity and strong mechanical and electrochemical stability [86]. ...
Chapter
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Electrochemical energy conversion and storage technologies play a crucial role in ensuring a sustainable energy future. In these regards, nanostructured carbon-based materials (NCMs) are very critical in the development of novel energy technologies and devices. NCMs include CNTs, graphene, fullerene, and ordered mesoporous carbon materials, which exist in different morphologies. NCMs offer great opportunities for effective modifications through surface functionalization, doping with heteroatoms, and fabrication of composites with organic or inorganic species. Particularly, the composites of NCMs with inorganic materials such as metallic NPs, metal oxide NPs, and their other derivatives (MNPs) have gained considerable recognition in electrochemical energy applications. These materials demonstrate distinct properties, including excellent thermal and electrical conductivity, large surface area, and chemical stability. Herein, we have highlighted some of the trends and outlooks in this exciting area, including fundamentals of these substances according to material science perspective. Besides, the latest research and development of multifunctional MNPs@NCMs composites for electrochemical energy applications have also been illustrated. Particularly, the utilization of these composites from the perspective of different electrochemical energy applications has been summarized, such as energy conversion processes like hydrogen evolution reactions (HER), oxygen reduction reactions (ORR), and energy storage devices like batteries and supercapacitors.
... Los Polioxometalatos (POM) en combinación con materiales grafénicos, según diversos estudios [39][40][41][42], han mostrado un gran potencial para su aplicación en SC de alto rendimiento. Los POM son compuestos que presentan diferentes estructuras moleculares tridimensionales (Lindqvis, Anderson, Keggin, y de Preyssler [43]), abarcan una rica variedad de tamaños y formas, sus unidades constructivas básicas son los poliedros oxometálicos MOx (x = 5, 6), donde M representa a metales de transición en estado de oxidación https://revistas.ujat.mx/index.php/jobs ...
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En este trabajo se reporta la obtención de materiales híbridos basados en POM (polioxometalatos) y GO (óxido de grafeno) preparados a partir de grafito expandido y exfoliado mecánicamente, con el propósito de acceder a su aplicación como electrodos en supercondensadores (SC). El procedimiento aquí reportado resultó en un proceso económico y con un tiempo corto de síntesis. Para la elaboración de los materiales se emplearon dos rutas sintéticas: usando a) punta ultrasónica y b) agitación magnética. El resto de las condiciones experimentales (solvente, tiempo de reacción, secado, etc.) se mantuvieron sin cambio. Se determinaron las propiedades fisicoquímicas y electroquímicas de los nanocompositos obtenidos usando DRX, Raman, Análisis elemental mediante EED-MEB y VC. Con base en los resultados se confirmó la obtención del material compuesto HPMo-GO esperado; los resultados también mostraron que la exfoliación mecánica, a la que fue sometido grafito expandido fue la clave para lograr una eficiencia de reacción similar tanto en la ruta magnética como en la ruta por punta ultrasónica.
... Graphene and carbon-based structures derived from graphene exhibit remarkable properties such as high electron mobility [1][2][3], high adsorption capacities [4][5][6], large surface areas [7,8], high electrical conductivity [9][10][11], and high thermal conductivity [12]. Thanks to these features, they find a wide range of applications, including sensors [13], capacitors [14,15], hydrogen storage [16][17][18][19], electrochemical devices [20], catalyst supports [21,22], gas purification [23,24], and the storage of hazardous gases [25]. The development and structural analysis of graphene-based architectures hold a significant position and are extensively studied [26][27][28][29][30][31]. ...
... Graphene materials have shown the potential to exceed their theoretical capacity limits, a phenomenon often attributed to the extra active points provided by structural defects and lattice edges in graphene [109] . However, the employment of graphene as an anode in LICs faces significant challenges owing to the formation of solid electrolyte interphase (SEI), because a significant amount of Li + are consumed in the formation of the SEI layer, resulting in a lower-than-expected overall capacity and performance of the LICs [110][111][112] . ...
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... Therefore, SIBs are growing remarkably as promising candidates to replace LIBs in large-scale energy storage systems, because of the abundant sodium reserves on earth 5,[7][8][9][10][11][12][13][14] . However, the commercial graphite employed in LIBs has been shown to be unsuitable for SIBs, because the radius of Na + (1.06 Å) is much larger than that of Li + (0.76 Å), which slows down the dynamism of the reaction and causes big volume expansion, leading to irreversible structural decomposition and capacity decay of SIBs 12,[15][16][17][18][19] . Therefore, it is urgent to find suitable anode materials with high conductivity, fast Na + diffusion channels and bouncy structure to tolerant volume change during charging and discharging processes. ...
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Conspectus Carbon-based two-dimensional (2D) functional materials exhibit potential across a wide spectrum of applications from chemical separations to catalysis and energy storage and conversion. In this Account, we focus on recent advances in the manipulation of 2D carbonaceous materials and their composites through computational design and simulations to address how the precise control over material structure at the atomic level correlates with enhanced functional properties such as gas permeation, selectivity, membrane transport, and charge storage. We highlight several key concepts in the computational design and tuning of 2D structures, such as controlled stacking, ion gating, interlayer pillaring, and heterostructure charge transfer. The process of creating and adjusting pores within graphene sheets is vital for effective molecular separation. Simulations show the power of controlling the offset distance between layers of porous graphene in precisely regulating the pore size to enhance gas separation and entropic selectivity. This strategy of controlled stacking extends beyond graphene to include covalent organic frameworks (COFs) such as covalent triazine frameworks (CTFs). Experimental assembly of the layers has been achieved through electrostatic interactions, thermal transformation, and control of side chain interactions. Graphene can interface with ionic liquids in various forms to enhance its functionality. A computational proof-of-concept showcases an ion-gating concept in which the interaction of anions with the pores in graphene allows the anions to dynamically gate the pores for selective gas transport. Realization of the concept has been achieved in both porous graphene and carbon molecular sieve membranes. Ionic liquids can also intercalate between graphene layers to form interlayer pillaring structures, opening the slit space. Grand canonical Monte Carlo simulations show that these structures can be used for efficient gas capture and separation. Experiments have demonstrated that the interlayer space can be tuned by the density of the pillars and that, when fully filled with ionic liquids and forming a confined interface structure, the graphene oxide membrane achieves much higher selectivity for gas separations. Moreover, graphene can interface with other 2D materials to form heterostructures where interfacial charge transfers take place and impact the function. Both ion transport and charge storage are influenced by both the local electric field and chemical interactions. Fullerene can be used as a building block and covalently linked together to construct a new type of 2D carbon material beyond a one-atom-thin layer that also has long-range-ordered subnanometer pores. The interstitial sites among fullerenes form funnel-shaped pores of 2.0–3.3 Å depending on the crystalline phase. The quasi-tetragonal phases are shown by molecular dynamics simulations to be efficient for H2 separation. In addition, defects such as fullerene vacancies can be introduced to create larger pores for the separation of organic solvents. In conclusion, the key to imputing functions to 2D carbonaceous materials is to create new interactions and interfaces and to go beyond a single-atom layer. First-principles and molecular simulations can further guide the discovery of new 2D carbonaceous materials and interfaces and provide atomistic insights into their functions.
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Atomically thin two-dimensional (2D) materials exhibit extraordinary optical, electrical, and mechanical properties. Many functional nanostructures and devices of exceptional performance based on 2D materials have been demonstrated. However, the processing of 2D materials remains challenging due to inadequacies that are mainly driven by high fabrication cost, complex steps, and inefficient impurity control. On the other hand, laser-aided processing techniques offer versatility, nanoscale precision, and high throughput. Numerous efforts have showcased the implementation of laser processing and functionalization of 2D materials to control their physical properties and optimize device functionality. In this Perspective, we summarize research progress on laser-enabled thinning, patterning, doping, and functionalization of 2D materials. Continuing advances in optical processing techniques are anticipated to further accelerate the deployment of 2D materials and devices in many fields, including photonics, optoelectronics, and sensor applications.
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Due to their low production cost, sodium‐ion batteries (SIBs) are considered attractive alternatives to lithium‐ion batteries (LIBs) for next generation sustainable and large‐scale energy storage systems. However, during the charge/discharge cycle, a large volume strain is resulted due to the presence of a large radius of sodium ions and high molar compared to lithium ions, which further leads to poor cyclic stability and lower reversible capacity. In the past, researchers have devoted significant efforts to explore various anode materials to achieve SIBs with high energy density. Hence, as a promising anode material for SIBs, the two‐dimensional (2D) materials including graphene and its derivatives and metal oxides have attracted remarkable attention due to their layered structure and superior physical and chemical properties. The inclusion of graphene and metal oxides with other nanomaterials in electrodes have led to the significant enhancements in electrical conductivity, reaction kinetics, capacity, rate performance and accommodating the large volume change respectively. Moreover, these 2D materials facilitated large surface areas and shorter paths for sodium ion adsorption and transportation respectively. In this review article, the fabrication techniques, structural configuration, sodium ion storage mechanism and its electrochemical performances will be introduced. Subsequently, an insight into the recent advancements in SIBs associated with 2D anode materials (graphene, graphene oxide (GO), transition metal oxides etc.) and other graphene‐like elementary analogues (germanene, stanine etc.) as anode materials respectively will be discussed. Finally, the key challenges and future perspectives of SIBs towards enhancing the sodium storage performance of graphene‐based electrode materials are discussed. In summary, we believe that this review will shed light on the path towards achieving long‐cycling life, low operation cost and safe SIBs with high energy density using 2D anode materials and to be suitably commercialized for large‐scale energy storage applications in the future.
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Interest in two-dimensional, sheet-like or flake-like carbon forms has expanded beyond monolayer graphene to include related materials with significant variations in layer number, lateral dimension, rotational faulting, and chemical modification. Describing this family of "graphene materials" has been causing confusion in the Carbon journal and in the scientific literature as a whole. The international editorial team for Carbon believes that the time has come for a discussion on a rational naming system for two-dimensional carbon forms. We propose here a first nomenclature for two-dimensional carbons that could guide authors toward a more precise description of their subject materials, and could allow the field to move forward with a higher degree of common understanding.
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Nitrogen doped graphene supported TiO2 hollow nanostructures varying from 10 to 15 nm were designed for sodium ion battery anode applications, which were obtained by a two-step technique hydrothermal-calcining process with urea as an inhibitor and a nitrogen source. The active nitrogen modified graphene matrix supported hollow hierarchical-pore nanoarchitectures, possessing high surface area, massive pores including micro-, meso- and macro-pores, and excellent structural stability, which are highly desirable for application in sodium ion batteries. Its interconnected carbon network ensures good conductivity and fast electron transport; the micro-, meso-, and macroporous nature effectively shortens the sodium ion diffusion path and provides the room necessary for volume expansion. The large specific surface area is beneficial for better contact between the electrode materials and the electrolyte. Such material exhibits excellent performance as anode materials for sodium ion batteries with a high reversible capacity, excellent cycle stability and superior rate capability. Besides, nitrogen and graphene play a crucial role in controlling the formation of the TiO2 hollow nanocrystals.
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A novel, flexible and binder-free reduced graphene oxide/Na2/3[Ni1/3Mn2/3]O2 composite electrode (GNNM) has been fabricated by a simple technique. Reduced graphene oxide (RGO) establishes stable electrically conductive structures in the GNNM electrode. The prepared GNNM electrode delivers 86 mA h g−1 at 0.1 C rate, and the capacity retention reaches 68.4% at 10 C rate. The discharge capacity of the GNNM electrode at 1 C rate can reach 80 mA h g−1 after 200 cycles.
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A series of novel composite membranes, based on sulfonated poly(ether ether ketone) (SPEEK) with various graphene oxide (GO) loadings, were employed and investigated in vanadium redox flow battery (VRFB) for the first time. The scanning electron microscopy images of the composite membranes revealed the uniform dispersion of GO nanosheets in the polymer matrix due to the interaction between GO and SPEEK, as confirmed by Fourier transform infrared spectra. The mechanical and thermal parameters of the composite membranes increased, while the VO2+ permeability decreased with increasing GO content. Random embedding of GO nanosheets in the membranes can serve as effective barriers to block the transport of vanadium ion, resulting in a significant decrease of vanadium ion permeability. The VRFB assembled with the composite membrane exhibited highly improved cell parameters and strikingly long cycling stability compared with commercial Nafion 117 membrane. With the protection of porous PTFE substrate, the pore-filling SPEEK/GO composite membrane based on VRFB ran for 1200 cycles with relatively low capacity decline.
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New ternary composites of MnO2 nanorods, polyaniline (PANI) and graphene oxide (GO) have been prepared by a two-step process. The 100 nm-long MnO2 nanorods with a diameter ~20 nm are conformably coated with PANI layers and fastened between GO layers. The MnO2 nanorods incorporated ternary composites electrode exhibits significantly increased specific capacitance than PANI/GO binary composite in supercapacitors. The ternary composite with 70% MnO2 exhibits a highest specific capacitance reaching 512 F/g and outstanding cycling performance, with ~97% capacitance retained over 5000 cycles. The ternary composite approach offers an effective solution to enhance the device performance of metal-oxide based supercapacitors for long cycling applications.
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To progress from the laboratory to commercial applications, it will be necessary to develop industrially scalable methods to produce large quantities of defect-free graphene. Here we show that high-shear mixing of graphite in suitable stabilizing liquids results in large-scale exfoliation to give dispersions of graphene nanosheets. X-ray photoelectron spectroscopy and Raman spectroscopy show the exfoliated flakes to be unoxidized and free of basal-plane defects. We have developed a simple model that shows exfoliation to occur once the local shear rate exceeds 10(4) s(-1). By fully characterizing the scaling behaviour of the graphene production rate, we show that exfoliation can be achieved in liquid volumes from hundreds of millilitres up to hundreds of litres and beyond. The graphene produced by this method performs well in applications from composites to conductive coatings. This method can be applied to exfoliate BN, MoS2 and a range of other layered crystals.
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In this communication, we introduce the concept of three dimensional (3D) battery electrodes to enhance the capacity per footprint area for lithium-sulfur battery. In such a battery, 3D electrode of sulfur embedded into porous graphene sponges (S-GS) was directly used as the cathode with large areal mass loading of sulfur (12 mg cm(-2)), approximately 6-12 times larger than that of most reports. The graphene sponges (GS) worked as a framework that can provide high electronic conductive network, abilities to absorb the polysulfides intermediate, and meanwhile mechanical support to accommodate the volume changes during charge and discharge. As a result, the S-GS electrode with 80 wt.% sulfur can deliver an extremely high areal specific capacitance of 6.0 mAh cm(-2) of the 11(th) cycle, and maintain 4.2 mAh cm(-2) after 300 charge-discharge cycles at a rate of 0.1C, representing an extremely low decay rate (0.08% per cycle after 300 cycles), which could be the highest areal specific capacity with comparable cycle stability among the rechargeable Li/S batteries reported ever.
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Distinctive rGO-supported MoS2 hybrids have been fabricated via a hydrothermal method followed by a heat treatment. Characterizations demonstrate that layered MoS2 and graphene nanosheets in the hybrids interlace with each other to form novel sandwich-structured microspheres, which exhibit preferable electrochemical performance in rechargeable Mg batteries.
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Varied graphene sheets were prepared from the graphite oxide (GO) with different degrees of oxidation and furthermore their structural characteristics and electrochemical properties as anode materials for Li-ion batteries were investigated. From the expandable graphite with a low oxidation level, the obtained graphene sheets had a thick and intact sheet structure with good crystallinity. Its specific surface area was quite low and no porous structure was detected. The graphene sheets prepared from the GO precursor with a high degree of oxidation were quite thin and disordered, along with high specific surface area and plenty of pores. These ultrathin graphene sheets demonstrated high reversible capacity mainly in the way of lithium absorption, where the specific surface area was the key structural parameter. The thick graphene sheets prepared from the expandable graphite had good crystallinity with few defects and pores, and had a similar lithium storage mechanism to graphite, whereby lithium storage is carried out by intercalation reactions.
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Li/S and Li/air cells have attracted much recent attention as potential successors to lithium ion batteries because of their exceptionally high energy density compared with current battery technology. Although the two new battery systems have the potential to satisfy the demand for a significant leap forward in energy storage technology, there remain significant problems to be addressed, including poor cycle stability and low rate capability for practical applications. To address these issues, much research effort has been invested. In particular, graphene, with its high surface area combined with catalytic properties, is considered to be a key potential material to advance Li/S and Li/air battery technology. Indeed, recent research into graphene has led to substantial performance improvements of Li/S and Li/air batteries. In this review, we describe recent achievements in Li/S and Li/air cells that have been facilitated by the application of graphene, together with the electrochemical reaction mechanisms and major issues facing both Li/S and Li/air batteries.
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Promising alternativee anode materials, including lithium titanate, cobalt oxides, silicon and tin, are identified and the recent developments in their synthesis methods are discussed.
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N and S codoping of graphene is realized by a novel approach: covalent functionalization of graphene oxide using 2-aminothiophenol as a source of both N and S followed by thermal treatment. The resulting N- and S-codoped graphene has potential applications in high-performance lithium-ion batteries and as a metal-free catalyst for oxygen reduction reaction.
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Electrochemical capacitors (ECs) have been widely applied in electronics, electric vehicles, aircrafts, energy storage devices, uninterrupted or emergency power supplies, and so on. An ideal EC should have high energy and/or powder density, good rate capability, and long cycling life. Recently, graphene, graphene derivatives, and their composites have been explored as the electrode materials of ECs to satisfy these requirements. In this Perspective, we review the recent development in synthesizing graphene materials for ECs and discuss the strategies of fabricating graphene-based macroscopic electrodes. Particularly, we highlight the importance of the specific surface area, conductivity, and heteroatom-doping of graphene sheets and the micro/nanostructures of their electrodes for controlling the performances of graphene-based ECs.
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Nitrogen-doped graphene nanosheets (NGS), prepared by a simple hydrothermal reaction of graphene oxide (GO) with urea as nitrogen source were studied as positive electrodes in vanadium redox flow battery (VRFB). The synthesized NGS with the nitrogen level as high as 10.12 atom% is proven to be a promising material for VRFB. The structures and electrochemical properties of the materials are investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry and electrochemical impendence spectroscopy. The results demonstrate that not only the nitrogen doping level but the nitrogen type in the NGS are significant for its catalytic activity towards the [VO]2+/[VO2]+ redox couple reaction. In more detail, among four types of nitrogen species (pyridinic-N, pyrrolic-N, quaternary-N, oxidic-N) doped into the graphene lattice, quaternary-N play mainly roles for improving the catalytic activity toward the [VO]2+/[VO2]+ couple reaction.
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We report the synthesis of a poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA)/graphene nanocomposite in which graphene is used as a support for improving electronic conductivity. The structure and morphology of the nanocomposite were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). These results reveal that a graphene surface is decorated by nanoparticles of PTMAwith an average size of 10 nm. The electrochemical performance of the PTMA/graphene composite as a cathode material in rechargeable magnesium batteries was investigated using cyclic voltammetry and galvanostatic charge/discharge techniques. In a "first generation" electrolyte Mg(AlCl2BuEt)2/tetrahydrofuran (THF) (0.25 mol·L-1), the material exhibits an initial discharge capacity of 81.2 mAh·g-1 at 22.8 mA·g-1. Further studies will focus on improving the capacity using electrolytes with a wider electrochemical window.
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A highly stable sodium ion battery anode was prepared by deposition of hydroperoxostannate on graphene oxide from hydrogen-peroxide-rich solution followed by sulfidization and 300 C heat treatment. The material was characterized by electron microscopy, powder X-ray diffraction and X-ray photoelectron spectroscopy which showed that the active material is mostly rhombohedral SnS 2 whose (001) planes were preferentially oriented in parallel to the graphene oxide sheets. The material exhibited >610 mA h g À1 charge capacity at 50 mA g À1 (with >99.6% charging efficiency) between 0 and 2 V vs. Na/Na + electrode, high cycling stability for over 150 cycles and very good rate performance, >320 mA h g À1 at 2000 mA g À1 .
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A composite consisting of iron oxide/graphene nanosheets (GNS) is synthesized by hydrothermal treatment of a mixture of graphitic oxide and FeCl2 in the presence of N2H4 as reducing agent. Special attention is given to the characterization of the iron oxide owing to the disparity of criteria found in literature to distinguish between maghemite (γ-Fe2O3) and magnetite (Fe3O4). Here, the oxide is accurately characterized as γ-Fe2O3. The beneficial effect of the simultaneous formation of GNS and γ-Fe2O3 is reflected in the capacity of the cell, which is much higher than those of the individual components. This may be the result of a synergistic effect of the good conducting properties of graphene, its buffering action on the volume changes undergone by γ-Fe2O3 on reacting with Li and the high capacity of this oxide. The composite also has good rate capability and can recover its capacity at low current intensities after prolonged cycling at high rates. The composite performs very well in a full cell configuration with LiFePO4 as cathode, where it exhibits an average discharge capacity of 122 mAh g−1 and excellent capacity retention over 50 cycles. In addition, the cell has good rate capability at current densities as high as 5C.
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High-shear mixing is now shown to be an effective approach for the exfoliation of large quantities of graphene and other two-dimensional materials, providing a viable route for the industrial scaling of applications based on these layered crystals. The commercial development of graphene and related two-dimensional materials is at present restrained by the lack of production techniques ready for industrial scale-up. Writing in Nature Materials, Coleman and colleagues now demonstrate that shear exfoliation can push the preparation of few-layer graphene solutions up the TRL ladder, projecting a route towards the use of this material in applications ranging from batteries and super capacitors to conductive fluids, coatings and gas-barrier composites. Coleman and colleagues' process of shear exfoliation to generate few-layer two-dimensional materials solutions is ambitious and characteristic of the detailed studies that are needed to proceed from discovery to a commercialized technology.
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Supercapacitors with porous carbon structures have high energy storage capacity. However, the porous nature of the carbon electrode, composed mainly of carbon nanotubes (CNTs) and graphene oxide (GO) derivatives, negatively impacts the volumetric electrochemical characteristics of the supercapacitors because of poor packing density (< 0.5 g cm-3). Herein, we report a simple method to fabricate highly dense and vertically aligned reduced graphene oxide (VArGO) electrodes involving simple hand-rolling and cutting processes. Due to their vertically aligned and opened-edge graphene structure, VArGO electrodes displayed high packing density and highly efficient volumetric and areal electrochemical characteristics, very fast electrolyte ion diffusion with rectangular CV curves even at a high scan rate (20 V/s), and the highest volumetric capacitance among known rGO electrodes. Surprisingly, even when the film thickness of the VArGO electrode was increased, its volumetric and areal capacitances were maintained.
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A layered SnS2 -reduced graphene oxide (SnS2 -RGO) composite is prepared by a facile hydrothermal route and evaluated as an anode material for sodium-ion batteries (NIBs). The measured electrochemical properties are a high charge specific capacity (630 mAh g(-1) at 0.2 A g(-1) ) coupled to a good rate performance (544 mAh g(-1) at 2 A g(-1) ) and long cycle-life (500 mAh g(-1) at 1 A g(-1) for 400 cycles).
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Rechargeable lithium batteries represent one of the most important developments in energy storage for 100 years, with the potential to address the key problem of global warming. However, their ability to store energy is limited by the quantity of lithium that may be removed from and reinserted into the positive intercalation electrode, Li(x)CoO(2), 0.5 < x < 1 (corresponding to 140 mA.h g(-1) of charge storage). Abandoning the intercalation electrode and allowing Li to react directly with O(2) from the air at a porous electrode increases the theoretical charge storage by a remarkable 5-10 times! Here we demonstrate two essential prerequisites for the successful operation of a rechargeable Li/O(2) battery; that the Li(2)O(2) formed on discharging such an O(2) electrode is decomposed to Li and O(2) on charging (shown here by in situ mass spectrometry), with or without a catalyst, and that charge/discharge cycling is sustainable for many cycles.
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Development of high-performance cathodes for sodium (Na)-ion batteries remains a great challenge, while low-cost, high-capacity Na2/3Fe1/2Mn1/2O2 is an attractive electrode material candidate comprised of earth-abundant elements. In this work, we designed and fabricated a freestanding, binder-free Na2/3Fe1/2Mn1/2O2@graphene composite via a filtration process. The porous composite led to excellent electrochemical performance due to the facile transport for electrons and ions which was characterized by electrochemical impedance spectroscopy at different temperatures. The electrode delivers a reversible capacity of 156 mAh/g with high Coulombic efficiency. The importance of a fluorinated electrolyte additive on the performance of this high voltage cathode in Na-ion batteries was also investigated.
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Preventing the stacking of graphene is essential to exploiting its full potential in energy-storage applications. The introduction of spacers into graphene layers always results in a change in the intrinsic properties of graphene and/or induces complexity at the interfaces. Here we show the synthesis of an intrinsically unstacked double-layer templated graphene via template-directed chemical vapour deposition. The as-obtained graphene is composed of two unstacked graphene layers separated by a large amount of mesosized protuberances and can be used for high-power lithium-sulphur batteries with excellent high-rate performance. Even after 1,000 cycles, high reversible capacities of ca. 530 mA h g(-1) and 380 mA h g(-1) are retained at 5 C and 10 C, respectively. This type of double-layer graphene is expected to be an important platform that will enable the investigation of stabilized three-dimensional topological porous systems and demonstrate the potential of unstacked graphene materials for advanced energy storage, environmental protection, nanocomposite and healthcare applications.
Article
High capacity electrodes based on a Si composite anode and a layered composite oxide cathode, Ni-rich Li[Ni0.75Co0.1Mn0.15]O2, are evaluated and combined to fabricate a high energy lithium ion battery. The Si composite anode, Si/C-IWGS (internally wired with graphene sheets), is prepared by a scalable sol–gel process. The Si/C-IWGS anode delivers a high capacity of >800 mAh g−1 with an excellent cycling stability of up to 200 cycles, mainly due to the small amount of graphene (∼6 wt%). The cathode (Li[Ni0.75Co0.1Mn0.15]O2) is structurally optimized (Ni-rich core and a Ni-depleted shell with a continuous concentration gradient between the core and shell, i.e., a full concentration gradient, FCG, cathode) so as to deliver a high capacity (>200 mAh g−1) with excellent stability at high voltage (∼4.3 V). A novel lithium ion battery system based on the Si/C-IWGS anode and FCG cathode successfully demonstrates a high energy density (240 Wh kg−1 at least) as well as an unprecedented excellent cycling stability of up to 750 cycles between 2.7 and 4.2 V at 1C. As a result, the novel battery system is an attractive candidate for energy storage applications demanding a high energy density and long cycle life.
Article
With the increased demand in energy resources, great efforts have been devoted to developing advanced energy storage and conversion systems. Graphene and graphene-based materials have attracted great attention owing to their unique properties of high mechanical flexibility, large surface area, chemical stability, superior electric and thermal conductivities that render them great choices as alternative electrode materials for electrochemical energy storage systems. This Review summarizes the recent progress in graphene and graphene-based materials for four energy storage systems, i.e., lithium-ion batteries, supercapacitors, lithium-sulfur batteries and lithium-air batteries.
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With the increasing demand for efficient and economic energy storage, Li-S batteries have become attractive candidates for the next-generation high-energy rechargeable Li batteries because of their high theoretical energy density and cost effectiveness. Starting from a brief history of Li-S batteries, this Review introduces the electrochemistry of Li-S batteries, and discusses issues resulting from the electrochemistry, such as the electroactivity and the polysulfide dissolution. To address these critical issues, recent advances in Li-S batteries are summarized, including the S cathode, Li anode, electrolyte, and new designs of Li-S batteries with a metallic Li-free anode. Constructing S molecules confined in the conductive microporous carbon materials to improve the cyclability of Li-S batteries serves as a prospective strategy for the industry in the future.
Article
We demonstrate that peat moss, a wild plant that covers 3% of the earth's surface, serves as an ideal precursor to create sodium ion battery (NIB) anodes with some of the most attractive electrochemical properties ever reported for carbonaceous materials. By inheriting the unique cellular structure of peat moss leaves, the resultant materials are composed of three-dimensional macroporous interconnected networks of carbon nanosheets (as thin as 60 nm). The peat moss tissue is highly cross-linked, being rich in lignin and hemicellulose, suppressing the nucleation of equilibrium graphite even at 1100°C. Rather the carbons form highly ordered pseudo-graphitic arrays with substantially larger intergraphene spacing (0.388 nm) than graphite (c/2 = 0.3354 nm). XRD analysis demonstrates that this allows for significant Na intercalation to occur even below 0.2V vs. Na/Na+. By also incorporating a mild (300°C) air activation step, we introduce hierarchical micro and mesoporosity that tremendously improves the high rate performance through facile electrolyte access and further reduced Na ion diffusion distances. The optimized structures (carbonization at 1100°C + activation) result in a stable cycling capacity of 298 mAhg-1 (after 10 cycles, 50 mAg-1), with ~ 150 mAhg-1 of charge accumulating between 0.1V and 0.001V with negligible voltage hysteresis in that region, nearly 100% cycling coulombic efficiency, and superb cycling retention and high rate capacity (255 mAhg-1 at the 210th cycle, stable capacity of 203 mAhg-1 at 500 mAg-1).
Article
We demonstrate the feasibility of a lithium ion battery (LIB) using graphene nanosheets (GNS) as the anode in combination with a LiNi0.5Mn1.5O4 (LNMO) high voltage, spinel-structure cathode. The GNS anode is characterized by a reversible capacity of the order of 600 mA h g(-1) and a working voltage of around 0.9 V, while the 4.8-V cathode has a theoretical capacity of 146.7 mA h g(-1). The full GNS/LiNi0.5Mn1.5O4 cell has an average working voltage of about 3.75 V and a capacity of the order of 100 mA h g(-1). The findings of this paper suggest that the graphene may be proposed as a suitable anode for application in lithium ion batteries.
Article
Nitrogen-doped graphene nanosheets (N-GNSs) displayed a discharge capacity two times greater than their pristine counterpart, as well as superior electrocatalytic activity as a cathode material for sodium-air batteries. The enhanced performance of N-GNSs is attributed to the active sites introduced by nitrogen doping.
Article
Recent progress on graphene/metal oxide composites as advanced electrode materials in lithium ion batteries (LIBs) and electrochemical capacitors (ECs) is described, highlighting the importance of synergistic effects between graphene and metal oxides and the beneficial role of graphene in composites for LIBs and ECs. It is demonstrated that, when the composites are used as electrode materials for LIBs and ECs, compared to their individual constituents, graphene/metal oxide composites with unique structural variables such as anchored, wrapped, encapsulated, sandwich, layered and mixed models have a significant improvement in their electrochemical properties such as high capacity, high rate capability and excellent cycling stability. First, an introduction on the properties, synthesis strategies and use of graphene is briefly given, followed by a state-of-the-art review on the preparation of graphene/metal oxide composites and their electrochemical properties in LIBs and ECs. Finally, the prospects and future challenges of graphene/metal oxide composites for energy storage are discussed.
Article
Two graphene materials, TRGO-1 and TRGO-2, prepared by the thermal exfoliation/reduction at 1000 °C of two graphite oxides with different characteristics, are investigated as positive electrodes in a vanadium redox flow battery (VRFB). A detailed study of their electrochemical response toward the [VO2+]/[VO2+] redox system is carried out through cyclic voltammetry, electrochemical impedance spectroscopy and charge/discharge experiments. As a consequence of the differences in the structure of the parent graphite oxides, TRGO-1 and TRGO-2 exhibit different structural and physicochemical properties resulting in significantly different electrochemical performances toward the vanadium redox reactions. TRGO-1 exhibits a markedly enhanced electrochemical activity (higher peak current densities and lower overpotentials) and a better kinetic reversibility toward the oxidation/reduction vanadium processes than TRGO-2. Furthermore, charge/discharge tests performed on two VRB single cells, the only differing component being the positive electrode, present higher coulombic, voltage and energy efficiency values in that battery containing the TRGO-1 electrode. The better results achieved with this sample are attributed to the higher degree of restoration of the 2D graphitic structure, and to the consequently higher electrical conductivity which increases the heterogeneous electron transfer rate. Moreover, residual hydroxyl groups present may act as active reaction sites and contribute to enhance its electrochemical response.