Showing papers on "Graphite published in 2016"
TL;DR: A simple, rapid method to reduce GO into pristine graphene using 1- to 2-second pulses of microwaves is reported using microwave-reduced GO (MW- rGO) as the channel material and into particularly high activity for MW-rGO catalyst support toward oxygen evolution reactions.
Abstract: Efficient exfoliation of graphite in solutions to obtain high-quality graphene flakes is desirable for printable electronics, catalysis, energy storage, and composites. Graphite oxide with large lateral dimensions has an exfoliation yield of ~100%, but it has not been possible to completely remove the oxygen functional groups so that the reduced form of graphene oxide (GO; reduced form: rGO) remains a highly disordered material. Here we report a simple, rapid method to reduce GO into pristine graphene using 1- to 2-second pulses of microwaves. The desirable structural properties are translated into mobility values of >1000 square centimeters per volt per second in field-effect transistors with microwave-reduced GO (MW-rGO) as the channel material and into particularly high activity for MW-rGO catalyst support toward oxygen evolution reactions.
640 citations
TL;DR: In this paper, the feasibility of a next-generation hybrid anode using silicon-nanolayer-embedded graphite/carbon was demonstrated, and the authors reported scalable synthesis of silicon-nolayer embedding graphite electrodes that display cycling stability at the industrial electrode density.
Abstract: Existing anode technologies are approaching their limits, and silicon is recognized as a potential alternative due to its high specific capacity and abundance. However, to date the commercial use of silicon has not satisfied electrode calendering with limited binder content comparable to commercial graphite anodes for high energy density. Here we demonstrate the feasibility of a next-generation hybrid anode using silicon-nanolayer-embedded graphite/carbon. This architecture allows compatibility between silicon and natural graphite and addresses the issues of severe side reactions caused by structural failure of crumbled graphite dust and uncombined residue of silicon particles by conventional mechanical milling. This structure shows a high first-cycle Coulombic efficiency (92%) and a rapid increase of the Coulombic efficiency to 99.5% after only 6 cycles with a capacity retention of 96% after 100 cycles, with an industrial electrode density of >1.6 g cm−3, areal capacity loading of >3.3 mAh cm−2, and <4 wt% binding materials in a slurry. As a result, a full cell using LiCoO2 has demonstrated a higher energy density (1,043 Wh l−1) than with standard commercial graphite electrodes. Silicon has long been recognized as a high-energy battery electrode but its commercialization faces significant barriers. Here the authors report scalable synthesis of silicon-nanolayer-embedded graphite electrodes that display cycling stability at the industrial electrode density.
534 citations
TL;DR: In this paper, the cycling performance of graphite anode in K-ion batteries is demonstrated with a reversible capacity of 246 mAh g/1 and 89% retention of the initial capacity after 200 cycles.
Abstract: Exceptional cycling performance of graphite anode in K-ion batteries is demonstrated with a reversible capacity of 246 mAh g–1 and 89% retention of the initial capacity after 200 cycles. Although the graphite anode experiences huge volume change and worse kinetics during K intercalation/deintercalation, the cycling stability delivered in K-ion batteries is comparable to that of Li-ion batteries using the same graphite anode. The combination of excellent electrochemical performance, the abundance and wide availability of K in earth's crust, and the well-developed technology of the graphite anode make the K-ion battery very attractive for offering a low cost battery chemistry for large-scale energy storage applications.
512 citations
TL;DR: These microsupercapacitors demonstrate comparable energy density to commercial lithium thin-film batteries, yet exhibit more than two orders of magnitude higher power density with good mechanical flexibility.
Abstract: All-solid-state, flexible, symmetric, and asymmetric microsupercapacitors are fabricated by a simple method in a scalable fashion from laser-induced graphene on commercial polyimide films, followed by electrodeposition of pseudocapacitive materials on the interdigitated in-plane architectures. These microsupercapacitors demonstrate comparable energy density to commercial lithium thin-film batteries, yet exhibit more than two orders of magnitude higher power density with good mechanical flexibility.
432 citations
TL;DR: This study provides a theoretical basis for industrial-scale recycling resources from spent LIBs by using oxygen-free roasting and wet magnetic separation to in situ recycle of cobalt, Lithium Carbonate and Graphite from mixed electrode materials.
355 citations
TL;DR: Hard carbon nanoparticles (HCNP) were synthesized by pyrolysis of a polyaniline precursor as discussed by the authors, and the measured Na+ cation diffusion coefficient (10−13−10−15 cm2−s−1) in the HCNP obtained at 1150°C is two orders of magnitude lower than that of Li+ in graphite.
319 citations
TL;DR: A 3D graphitic foam vertically aligned graphitic structure and a low density of defects is derived through chloroaluminate anion intercalation of graphite followed by thermal expansion and electrochemical hydrogen evolution to provide excellent Al-ion battery characteristics.
Abstract: A 3D graphitic foam vertically aligned graphitic structure and a low density of defects is derived through chloroaluminate anion intercalation of graphite followed by thermal expansion and electrochemical hydrogen evolution. Such aligned graphitic structure affords excellent Al-ion battery characteristics with a discharge capacity of ≈60 mA h g-1 under a high charge and discharge current density of 12 000 mA g-1 over ≈4000 cycles.
282 citations
TL;DR: Electrochemical exfoliation of graphite allowed the formation of highly oxidized graphene with a C/O ratio close to 4.0 and represents a possible avenue for the mass production of graphene oxide as valid alternative to the current laborious and dangerous chemical procedures, which also have limited scalability.
Abstract: Top-down methods are of key importance for large-scale graphene and graphene oxide preparation. Electrochemical exfoliation of graphite has lately gained much interest because of the simplicity of execution, the short process time, and the good quality of graphene that can be obtained. Here, we test three different electrolytes, that is, H2 SO4 , Na2 SO4 , and LiClO4 , with a common exfoliation procedure to evaluate the difference in structural and chemical properties that result for the graphene. The properties are analyzed by means of scanning transmission electron microscopy (STEM), Raman spectroscopy, and X-ray photoelectron spectroscopy. We then tested the graphene materials for electrochemical applications, measuring the heterogeneous electron transfer (HET) rates with a Fe(CN)6 (3-/4-) redox probe, and their capacitive behavior in alkaline solutions. We correlate the electrochemical features with the presence of structural defects and oxygen functionalities on the graphene materials. In particular, the use of LiClO4 during the electrochemical exfoliation of graphite allowed the formation of highly oxidized graphene with a C/O ratio close to 4.0 and represents a possible avenue for the mass production of graphene oxide as valid alternative to the current laborious and dangerous chemical procedures, which also have limited scalability.
228 citations
TL;DR: In this article, the authors report a method of overcoming the capacity limit of conventional graphite anodes by reversibly plating and stripping Li metal within the internal space of massive artificial graphite particles.
223 citations
TL;DR: It is found that the uniform immobilization of ZrO2 nanoparticles on the GF not only significantly promotes the accessibility of vanadium electrolyte, but also provides more active sites for the redox reactions, thereby resulting in better electrochemical activity and reversibility toward the VO(2+)/VO2(+) and V( 2+)/V(3+) red ox reactions as compared with those of GF.
Abstract: To improve the electrochemical performance of graphite felt (GF) electrodes in vanadium flow batteries (VFBs), we synthesize a series of ZrO2-modified GF (ZrO2/GF) electrodes with varying ZrO2 contents via a facile immersion-precipitation approach. It is found that the uniform immobilization of ZrO2 nanoparticles on the GF not only significantly promotes the accessibility of vanadium electrolyte, but also provides more active sites for the redox reactions, thereby resulting in better electrochemical activity and reversibility toward the VO2+/VO2+ and V2+/V3+ redox reactions as compared with those of GF. In particular, The ZrO2/GF composite with 0.3 wt % ZrO2 displays the best electrochemical performance with voltage and energy efficiencies of 71.9% and 67.4%, respectively, which are much higher than those of 57.3% and 53.8% as obtained from the GF electrode at 200 mA cm–2. The cycle life tests demonstrate that the ZrO2/GF electrodes exhibit outstanding stability. The ZrO2/GF-based VFB battery shows neglig...
212 citations
TL;DR: Exfoliated graphite (EG) refers to graphite that has a degree of separation of a substantial portion of the carbon layers in the graphite as discussed by the authors, which allows the formation of EG compacts and flexible graphite sheet without binder.
Abstract: Exfoliated graphite (EG) refers to graphite that has a degree of separation of a substantial portion of the carbon layers in the graphite. Graphite nanoplatelet (GNP) is commonly prepared by mechanical agitation of EG. The EG exhibits clinginess, due to its cellular structure, but GNP does not. The clinginess allows the formation of EG compacts and flexible graphite sheet without a binder. The exfoliation typically involves intercalation, followed by heating. Upon heating, the intercalate vaporizes and/or decomposes into smaller molecules, thus causing expansion and cell formation. The sliding of the carbon layers relative to one another enables the cell wall to stretch. The exfoliation process is accompanied by intercalate desorption, so that only a small portion of the intercalate remains after exfoliation. The most widely used intercalate is sulfuric acid. The higher concentration of residue in unwashed EG causes the relative dielectric constant (50 Hz) of the EG to be 360 (higher than 120 for KOH-activated GNP), compared to the value of 38 for the water-washed case. An EG compact is obtained by the compression of EG at a pressure lower than that used for the fabrication of flexible graphite. Compared to flexible graphite, EG compacts are mechanically weak, but they exhibit viscous character, out-of-plane electrical/thermal conductivity and liquid permeability. The viscous character (flexural loss tangent up to 35 for the solid part of the compact) stems from the sliding of the carbon layers relative to one another, with the ease of the sliding enhanced by the exfoliation process.
TL;DR: In this article, an NMC cathode and a graphite anode were investigated under operating conditions using X-ray absorption spectroscopy, which allowed both the time/voltage and spatially resolved determination of metal concentration and oxidation state on the graphite electrode.
Abstract: In Li-ion batteries the dissolution of transition metals from the cathode and their subsequent deposition on the anode are known to contribute to capacity fading. In this study, we investigate these processes using an NMC cathode and a graphite anode under operating conditions using X-ray absorption spectroscopy. The experiments are carried out in an operando cell, which allows both the time/voltage and spatially resolved determination of metal concentration and oxidation state of transition metal deposits on the graphite electrode. NMC shows a strong increase of the metal dissolution rate, if the upper cut off potential exceeds 4.6 V. Under operating conditions, the oxidation state of manganese, cobalt and nickel are found to be always +2 both on lithiated and delithiated graphite. In contrast, manganese is found to be present in the metallic state on lithiated graphite in the ex situ analysis, thus highlighting the importance of the operando characterization.
TL;DR: In this article, three-dimensional rod-like carbon microstructures derived from natural ramie fibers and two-dimensional carbon nanosheets derived from corncobs have been fabricated by heat treatment at 700°C under argon atomsphere.
TL;DR: In this paper, the current status and future demand of flake graphite in the market are discussed and a new perspective towards the future concept of battery recycling is also pointed out.
Abstract: Graphite is currently the state-of-the-art anode material for most of the commercial lithium ion batteries. Among different types of natural graphite, flake graphite has been recently recognized as one of the critical materials due to the predicted future market growth of lithium ion batteries for vehicular applications. Current status and future demand of flake graphite in the market are discussed. It was found that flake graphite could become a critical material in the near future for countries such as the United States and members of the European Union with no graphite production. Recycling of flake graphite from its different waste resources is proposed as a potential solution to meet the future demand of graphite. The current status of graphite anodes in the present recycling technologies of spent lithium ion batteries was reviewed. The limitation of current technologies and a new perspective towards the future concept of “battery recycling” were also pointed out. Challenges in recycling battery grade flake graphite from spent lithium ion batteries and possible research opportunities in this regard were introduced.
TL;DR: In this article, the preparation and properties of reduced graphene oxide (rGO) and graphene nanosheets (GNSs) reinforcement of aluminium matrix nanocomposites (AMCs) are reported.
TL;DR: This experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites.
Abstract: The shock-induced transition from graphite to diamond has been of great scientific and technological interest since the discovery of microscopic diamonds in remnants of explosively driven graphite. Furthermore, shock synthesis of diamond and lonsdaleite, a speculative hexagonal carbon polymorph with unique hardness, is expected to happen during violent meteor impacts. Here, we show unprecedented in situ X-ray diffraction measurements of diamond formation on nanosecond timescales by shock compression of pyrolytic as well as polycrystalline graphite to pressures from 19 GPa up to 228 GPa. While we observe the transition to diamond starting at 50 GPa for both pyrolytic and polycrystalline graphite, we also record the direct formation of lonsdaleite above 170 GPa for pyrolytic samples only. Our experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites.
TL;DR: In this paper, carbon species removal from a Fe-Ni catalyst supported on MgAl2O4 after methane dry reforming at 1023 K, atmospheric pressure and a CH4/CO2 molar ratio of 1:1.
Abstract: Carbon species removal was studied from a Fe–Ni catalyst supported on MgAl2O4 after methane dry reforming at 1023 K, atmospheric pressure and a CH4/CO2 molar ratio of 1:1. The deactivated and regenerated catalysts were characterized using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and energy-dispersive X-ray spectroscopy (EDX)-STEM mapping. The catalyst regeneration was studied by CO2 and O2 temperature programmed oxidation (TPO) and by operando time-resolved X-ray diffraction (XRD). A transient response technique, Temporal analysis of products (TAP), was applied to investigate the isothermal carbon species gasification. Two different types of carbon species, graphitic and amorphous, were present after reaction. CO2 oxidation could remove part of the carbon species, although EDX-STEM mapping showed the presence of carbon species located far from active metals phase even after CO2–TPO at 1123 K. Carbon species removal by CO2 involves two contributions: (1) the dissociation of CO2 over Ni followed by the oxidation of carbon species by surface oxygen; (2) Fe oxidation by CO2 and subsequent carbon species oxidation by Fe oxide lattice oxygen. The oxidation of carbon species by O2 was identified from temperature programmed and isothermal experiments as a process including two processes: (1) oxidation of surface carbon by lattice oxygen and (2) particles migration to carbon species deposited far from active metals and subsequent oxidation through lattice oxygen of the iron and/or nickel oxides. The contribution of oxygen spillover in carbon gasification was considered to be negligible.
TL;DR: In this article, hard carbons (HC) prepared by cellulose pyrolysis were investigated with varying pyrolysisation temperature from 700°C to 1600°C, and different tests in Na//HC cells with NaPF6 ethylene carbonate/dimethyl carbonate (EC/DMC).
TL;DR: An exceptionally stable honeycomb carbon allotrope obtained by deposition of vacuum-sublimated graphite is reported, demonstrating high levels of physical absorption of various gases unattainable in other carbon forms such as fullerites or nanotubes.
Abstract: We report an exceptionally stable honeycomb carbon allotrope obtained by deposition of vacuum-sublimated graphite. The allotrope structures are derived from our low temperature electron diffraction and electron microscopy data. These structures can be both periodic and random and are built exclusively from sp^{2}-bonded carbon atoms, and may be considered as three-dimensional graphene. They demonstrate high levels of physical absorption of various gases unattainable in other carbon forms such as fullerites or nanotubes. These honeycomb structures can be used not only for storage of various gases and liquids but also as a matrix for new composites.
TL;DR: In this paper, an environmental friendly, economical and facile one-pot electrochemical method was developed to synthesize sulfur-doped graphene (S-GN), in which Sodium thiosulphate (Na2S2O3), in addition to acting as a sulfur source, also catalyzed the exfoliation process, resulting in sulfurdoped GN structures.
Abstract: Doping with heteroatoms has become a significant strategy for modifying the electronic properties and enhancing the electrochemical properties of graphene (GN). In this study, an environmental friendly, economical and facile one pot electrochemical method was developed to synthesize sulfur-doped graphene (S-GN). Sodium thiosulphate (Na2S2O3), in addition to acting as a sulfur source, also catalyzed the exfoliation process, resulting in sulfur-doped GN structures. The exfoliation of graphite to GN and sulfur (S) doping occurred simultaneously resulting in well dispersed S-GN frameworks. Transmission electron microscopy and high-resolution transmission electron microscopy revealed the presence of the heteroatom in S-GN, and X-ray photoelectron spectroscopy confirmed the high S content (3.47%), as well as the existence of high-quality sulphureted species (mainly as C–S–C–). The incorporation of S species in GN during the exfoliation process modified the surface chemistry of carbon in the GN. The electrochemical performance of the as-prepared S-GN electrode exhibited a high specific capacitance of 320 F g−1 at a current density of 3 A g−1 and excellent cycling stability up to 1500 cycles as well as high energy density of 160 W h kg−1 at a power density of 5161 W kg−1 in an aqueous electrolyte.
TL;DR: In this paper, a high-performance OER catalyst, nitrogen and sulfur codoped graphite foam (NSGF), was reported, which was prepared from commercial graphite foil and directly applied as an electrocatalytic electrode without using a current collector and polymeric binder.
Abstract: The oxidation of water to produce oxygen gas is related to a variety of energy storage systems. Thus, the development of efficient, cheap, durable, and scalable electrocatalysts for oxygen evolution reaction (OER) is of great importance. Here, a high-performance OER catalyst, nitrogen and sulfur codoped graphite foam (NSGF) is reported. This NSGF is prepared from commercial graphite foil and directly applied as an electrocatalytic electrode without using a current collector and a polymeric binder. It exhibits an extremely low overpotential of 0.380 V to reach a current density of 10 mA cm−2 and shows fast kinetics with a small Tafel slope of 96 mV dec−1 in 0.1 m KOH. This electrocatalytic performance is superior or comparable to those of previously reported metal-free OER catalysts.
TL;DR: In this paper, an analytical formula has been developed to predict electrical conductivity of composites reinforced by conductive fillers such as polymer-based carbon composites, and the model is performed by MATLAB software.
TL;DR: It is demonstrated that the best performance of recycled graphite anodes can be achieved when electrolyte extraction is performed using subcritical CO2, and comparative studies reveal that, in the best case, the electrochemical performance of recycling graphite exceeds the benchmark consisting of a newly synthesized graphiteAnode.
Abstract: The present work reports on challenges in utilization of spent lithium-ion batteries (LIBs)-an increasingly important aspect associated with a significantly rising demand for electric vehicles (EVs). In this context, the feasibility of anode recycling in combination with three different electrolyte extraction concepts is investigated. The first method is based on a thermal treatment of graphite without electrolyte recovery. The second method additionally utilizes a subcritical carbon-dioxide (subcritical CO2 )-assisted electrolyte extraction prior to thermal treatment. And the final investigated approach uses supercritical carbon dioxide (scCO2 ) as extractant, subsequently followed by the thermal treatment. It is demonstrated that the best performance of recycled graphite anodes can be achieved when electrolyte extraction is performed using subcritical CO2 . Comparative studies reveal that, in the best case, the electrochemical performance of recycled graphite exceeds the benchmark consisting of a newly synthesized graphite anode. As essential efforts towards electrolyte extraction and cathode recycling have been made in the past, the electrochemical behavior of recycled graphite, demonstrating the best performance, is investigated in combination with a recycled LiNi1/3 Co1/3 Mn1/3 O2 cathode.
TL;DR: Detailed investigations show an increased charge collection in this device compared to that without the SWCNT additive, and the CH3NH3PbI3-based device achieves a power conversion efficiency of 14.7% under AM 1.5G illumination.
Abstract: A single walled carbon nanotube (SWCNT) possesses excellent hole conductivity. This work communicates an investigation of perovskite solar cells using a mesoscopic TiO2/Al2O3 structure as a framework in combination with a certain amount of SWCNT-doped graphite/carbon black counter electrode material. The CH3NH3PbI3-based device achieves a power conversion efficiency of 14.7% under AM 1.5G illumination. Detailed investigations show an increased charge collection in this device compared to that without the SWCNT additive.
TL;DR: In this paper, the electrocatalytic activity of pure graphite (PG), graphene oxide (GO), and carbon nanotubes (CNT) dispersed on glassy carbon (GC) was investigated for the electrochemical CO2 reduction reaction (CO2RR) in aqueous solution.
Abstract: Carbon materials are frequently used as supports for electrocatalysts because they are conductive and have high surface area. However, recent studies have shown that these materials can contain significant levels of metallic impurities that can dramatically alter their electrochemical properties. Here, the electrocatalytic activity of pure graphite (PG), graphene oxide (GO), and carbon nanotubes (CNT) dispersed on glassy carbon (GC) are investigated for the electrochemical CO2 reduction reaction (CO2RR) in aqueous solution. It was observed that GO and CNT dispersed on GC all exhibit significant electrochemical activity that can be ascribed to impurities of Ni, Fe, Mn, and Cu. The level of Cu in GO can be particularly high and is the cause for the appearance of methane in the products produced over this material when it is used for the CO2RR. Washing these supports in ultrapure nitric acid is effective in removing the metal impurities and results in a reduction in the electrochemical activity of these form...
TL;DR: In this paper, a method of creating lightweight, aluminum-metallic, composite materials under halides melt at temperatures 973 −1073 ǫ under air atmosphere is proposed.
TL;DR: This work demonstrates a method of mass production of graphene nanoplatelets (GNPs) by exfoliation of flake graphite in the tricomponent system made by a combination of ammonium persulfate ((NH4)2S2O8), concentrated sulfuric Acid, and fuming sulfuric acid.
Abstract: Successful application of graphene is hampered by the lack of cost-effective methods for its production. Here, we demonstrate a method of mass production of graphene nanoplatelets (GNPs) by exfoliation of flake graphite in the tricomponent system made by a combination of ammonium persulfate ((NH4)2S2O8), concentrated sulfuric acid, and fuming sulfuric acid. The resulting GNPs are tens of microns in diameter and 10–35 nm in thickness. When in the liquid phase of the tricomponent media, graphite completely loses its interlayer registry. This provides a ∼100% yield of GNPs from graphite in 3–4 h at room temperature or in 10 min at 120 °C.
TL;DR: A novel fabrication method of graphite/polypropylene (PP) composites with high thermal conductivity in which graphite flakes construct a continuous thermally conductive network.
Abstract: Thermally conductive polymer composites have aroused significant academic and industrial interest for several decades. Herein, we report a novel fabrication method of graphite/polypropylene (PP) composites with high thermal conductivity in which graphite flakes construct a continuous thermally conductive network. The thermal conductivity coefficient of the graphite/PP composites is markedly improved to be 5.4 W/mK at a graphite loading of 21.2 vol %. Such a great improvement of the thermal conductivity is ascribed to the occurrence of orientations of crystalline graphite flakes with large particles around PP resin particles and the formation of a perfect thermally conductive network. The model of Hashin-Shtrikman (HS) is adopted to interpret the outstanding thermally conductive property of the graphite/PP composites. This work provides a guideline for the easy fabrication of thermally conductive composites with network structures.
TL;DR: In this article, a vanadium redox flow battery (VRFB) with a carbon nanoparticle-decorated graphite felt electrode for the battery has been presented, exhibiting a significantly reduced ohmic loss through reducing electrode thickness, an increased surface area and improved electrocatalytic activity by coating carbon nanoparticles.
TL;DR: In this article, carbon nanofibres (CNFs) and graphite flake microparticles were added to thermoplastic polystyrene polymer with the aim of making new conductive blends suitable for 3D-printing.
Abstract: Carbon nanofibres (CNFs) and graphite flake microparticles were added to thermoplastic polystyrene polymer with the aim of making new conductive blends suitable for 3D-printing. Various polymer/carbon blends were evaluated for suitability as printable, electroactive material. An electrically conducting polystyrene composite was developed and used with commercially available polystyrene (HIPS) to manufacture electrodes suitable for electrochemical experiments. Electrodes were produced and evaluated for cyclic voltammetry of aqueous 1,1’-ferrocenedimethanol and differential pulse voltammetry detection of aqueous Pb2+ via anodic stripping. A polystyrene/CNF/graphite (80/10/10 wt%) composite provides good conductivity and a stable electrochemical interface with well-defined active geometric surface area. The printed electrodes form a stable interface to the polystyrene shell, give good signal to background voltammetric responses, and are reusable after polishing.