Graphene Anode Research Articles

Confined growth of Fe2O3 nanoparticles by holey graphene for enhanced sodium-ion storage

Metal oxide/graphene hybrids are promising anode materials for sodium-ion batteries (SIBs). However, avoiding the overgrowth of the metal oxide nanoparticles (NPs) with high content and eliminating the blocking effect of graphene towards ion diffusion are still hard to achieve, lowering the active material utilization. Herein, we prepare a Fe2O3/holey graphene (FHG) anode for SIBs with enhanced electrochemical performance. The introduced hole edges and functional groups in holey graphene help adsorb Fe3+ and anchor the formed NPs to avoid their aggregation through the formation of Fe–O–C bonds, effectively confining the growth of Fe2O3 NPs and enhance their electrochemical activity. Besides, the holes on graphene facilitate the ion-transport to enhance the utilization of Fe2O3 and decrease the ion-diffusion resistance. As a result, FHG shows the uniformly distributed NPs with around 30 nm with a high Fe2O3 content of ∼73 wt%, and thus, the improved reversible capacity (923 mAh g−1 at 0.1 A g−1) and rate capability (318 mAh g−1 at 2 A g−1), much better than the Fe2O3/graphene hybrid without holes. This work demonstrates an effective method to improve the utilization and reaction kinetics of metal oxide, which can be extended to prepare the other hybrid materials for different applications.

The Maximum Efficiency and Parametric Optimum Selection of a Solar-Driven Thermionic-Photovoltaic Integrated Device

A neoteric model of the solar-driven integrated device mainly composed of a thermionic generator (TIG) with a graphene-based anode and a thermophotovoltaic cell is presented, where the major irreversible losses inside and outside the system are considered. The analytical expressions for the power output and efficiency of two subsystems and the integrated device are derived. The temperatures of the emitter and collector are determined through heat balance equations. The effects of the voltage outputs of the generator and cell, area ratio of the absorber to the emitter, bandgap energy of the cell, and solar concentration factor on the systemic performance are evaluated. Several main parameters are optimized and parametric selection criteria are provided. The maximum efficiencies of the integrated device operated at different conditions are calculated. For example, under 1000 solar concentration, the efficiency of the integrated device attains 45.23%, which is obviously higher than that of a single solar-driven TIG (STIG) or other existing hybrid systems with a traditional TIG. It is found that replacing metallic anode by graphene anode and integrating a photovoltaic cell into the STIG largely enhance the conversion efficiency of solar energy.

3D printed silicon-few layer graphene anode for advanced Li-ion batteries.

The printing of three-dimensional (3D) porous electrodes for Li-ion batteries is considered a key driver for the design and realization of advanced energy storage systems. While different 3D printing techniques offer great potential to design and develop 3D architectures, several factors need to be addressed to print 3D electrodes, maintaining an optimal trade-off between electrochemical and mechanical performances. Herein, we report the first demonstration of 3D printed Si-based electrodes fabricated using a simple and cost-effective fused deposition modelling (FDM) method, and implemented as anodes in Li-ion batteries. To fulfil the printability requirement while maximizing the electrochemical performance, the composition of the FDM filament has been engineered using polylactic acid as the host polymeric matrix, a mixture of carbon black-doped polypyrrole and wet-jet milling exfoliated few-layer graphene flakes as conductive additives, and Si nanoparticles as the active material. The creation of a continuous conductive network and the control of the structural properties at the nanoscale enabled the design and realization of flexible 3D printed anodes, reaching a specific capacity up to ∼345 mA h g−1 at the current density of 20 mA g−1, together with a capacity retention of 96% after 350 cycles. The obtained results are promising for the fabrication of flexible polymeric-based 3D energy storage devices to meet the challenges ahead for the design of next-generation electronic devices.

Cellulose Derived Graphene/Polyaniline Nanocomposite Anode for Energy Generation and Bioremediation of Toxic Metals via Benthic Microbial Fuel Cells.

Benthic microbial fuel cells (BMFCs) are considered to be one of the eco-friendly bioelectrochemical cell approaches nowadays. The utilization of waste materials in BMFCs is to generate energy and concurrently bioremediate the toxic metals from synthetic wastewater, which is an ideal approach. The use of novel electrode material and natural organic waste material as substrates can minimize the present challenges of the BMFCs. The present study is focused on cellulosic derived graphene-polyaniline (GO-PANI) composite anode fabrication in order to improve the electron transfer rate. Several electrochemical and physicochemical techniques are used to characterize the performance of anodes in BMFCs. The maximum current density during polarization behavior was found to be 87.71 mA/m2 in the presence of the GO-PANI anode with sweet potato as an organic substrate in BMFCs, while the GO-PANI offered 15.13 mA/m2 current density under the close circuit conditions in the presence of 1000 Ω external resistance. The modified graphene anode showed four times higher performance than the unmodified anode. Similarly, the remediation efficiency of GO-PANI was 65.51% for Cd (II) and 60.33% for Pb (II), which is also higher than the unmodified graphene anode. Furthermore, multiple parameters (pH, temperature, organic substrate) were optimized to validate the efficiency of the fabricated anode in different environmental atmospheres via BMFCs. In order to ensure the practice of BMFCs at industrial level, some present challenges and future perspectives are also considered briefly.

Understanding Excess Li Storage beyond LiC6 in Reduced Dimensional Scale Graphene.

A phenomenon is observed in which the electrochemical performances of porous graphene electrodes show unexpectedly increasing capacities in the Li storage devices. However, despite many studies, the cause is still unclear. Here, we systematically present the reason for the capacity enhancements of the pristine graphene anode under functional group exclusion through morphological control and crystal structure transformation. The electrochemical synergy of both the edge effect and surface effect of the reduced dimensional scale graphene in an open-porous structure facilitates significantly enhanced capacity through multidimensional Li-ion accessibility and accumulation of Li atoms. Furthermore, the Stone-Wales defects boosted during Li insertion and extraction promote a capacity elevation beyond the theoretical capacity of the carbon electrode even after long-term cycles at high C-rates. As a result, the morphologically controlled graphene anode delivers the highest reversible capacity of 3074 mA h g-1 with a 163% capacity increase after 2000 cycles at 5 C. It also presents a gradually increasing capacity up to 1102 mA h g-1 even at 50 C without an evident capacity fading tendency. This study provides valuable information into the practical design of ultralight and high-rate energy storage devices.

An influence of temperature on the lithium ions behavior for starch-based carbon compared to graphene anode for LIBs by the electrochemical impedance spectroscopy (EIS)

The main aim of this research is the evaluation of the diffusion coefficient, ionic conductivity of carbon-based anode materials (graphene and carbon from corn starch (CSC)) at different temperature conditions. This serves to appraise those materials for the more demanding cell conditions and reducing the explosiveness of the battery. Additionally, the very innovative part of the research is the designation of the kinetic and thermodynamic parameters for two different models for lithium ions diffusion during the charge of the half-cell. The activation energy of the diffusion process has the values in the range of 37.37–39.95 kJ mol−1 for CSC compared to graphene (43.80–46.38 kJ mol−1). Additionally, the lithiation process is thermodynamically endothermic and forced. The use of the carbon based on the corn starch as the anode material is connected with the “Green Chemistry” aspect, which improves the availability of materials, biodegradability and cost of the system. All investigations were carried out using the Electrochemical Impedance Spectroscopy (EIS), what also shows the possibilities of this technique to evaluate the important parameters during the work of the cell and optimization, and the thermodynamic and kinetic response of the system against different conditions.

(Invited) Controlled Assembly of 3D Graphene Electrodes for Enhanced Alkali Metal Storage

Graphene has been intensively investigated as an electrode material for energy storage devices thanks to its large surface area and excellent electrical conductivity. However, the restacking of graphene sheets is inevitable during the solution process due to π–π and hydrophobic interactions, which reduces the available surface area. Recently, 3D structured crumpled graphene has emerged as an promising electrode material due to its aggregation-resistive property.In this study, we will introduce our recent efforts to assemble 3D structured crumpled graphene anodes through the stacking engineering process for Li-, Na-, K-ion batteries. We reveal the role of defects in improving the charge storage performance through the surface-controlled charge storage mechanism. The crumpled graphene anodes exhibited high capacity with excellent rate-performance and cycling stability. We further evaluate the temperature-dependent performance of 3D graphene anodes, demonstrating their superior charge storage performance in extreme cold environments. Finally, we will discuss anodic electrochemical exfoliation of graphite for the fast production of graphene at low cost with moderate quality.

High Performance Lithium Battery Anodes from Non-Water Based Graphene

High performance lithium battery anode plates were made from processed arc discharge graphene. Arc discharge graphene has been produced from glow electrolytic thermal arc discharging of graphite rods [1-3], different from graphene or reduced graphene prepared through other means [4-11], because it maintains high crystallinity and planar characteristics of graphite marked by low ID/IG and XRD peak (2θ = 26 ⁰C). Arc discharge Graphene was sonicated in NMP for hours until fully exfoliated and able to film coat without impediments on the rougher side of the electrode copper film. Sonicated Graphene was dried in the vacuum oven. Anode plates were prepared by homogenizing the sonicated graphene in PVDF saturated NMP (0.53% NMP; 4% superP carbon black; and 2.25wt% PVDF) for 1 hr. The anode slurry was coated on the copper plates using automatic doctor blade film coater at a speed of 100mm/min. Anode plates were dried at 80 ⁰C for and cured for 120 ⁰C for 2 hrs in vacuum oven. Coin cells of NMC//HGR were made and tested in CT2001A. The capacity of the anode cycled at 1C was ~1083mAhg-1. This very high capacity of the graphene anode represents 188.3% increase over nominal graphite anodes, and one of the highest reported in published literature.

Extremely efficient flexible organic solar cells with a graphene transparent anode: Dependence on number of layers and doping of graphene

Graphene has shown tremendous potential as a transparent conductive electrode (TCE) for flexible organic solar cells (OSCs). However, the trade-off between electrical conductance and transparency as well as surface roughness of the graphene TCE with increasing layer number limits power conversion efficiency (PCE) enhancement and its use for large-area OSCs. Here, we use a 300 nm-thick poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)]:[6,6]-phenyl-C71-butyric acid methyl ester blend as the photoactive layer and a benzimidazole (BI)-doped graphene as the transparent anode to demonstrate efficient OSCs with good flexibility. It is found that 3 layer (L) graphene had the best balance between sheet resistance, optical transmittance and surface roughness for optimized cell design. A 0.2 cm2 cell with a 3L BI-doped graphene anode had a PCE of 6.85%, which is one of the highest PCE values reported so far for flexible graphene anode-based OSCs. The flexible cells were mechanically robust, showing only a small performance degradation during up to 250 flexing cycles. Moreover, the combination of the thick photoactive layer with the optimized 3L BI-doped graphene TCE enabled production of 1.6 cm2 flexible OSCs with a PCE of 1.8%. Our work illustrates the importance of graphene TCE development for flexible OSCs as well as other wearable optoelectronic devices.

Sodium Adsorption and Intercalation in Bilayer Graphene Doped with B, N, Si and P: A First-Principles Study

Heteroatom-doped graphene is a potential anode material in sodium-ion batteries (SIBs). However, understanding the mechanisms of Na adsorption on the surface and intercalation in the interlayer remains a critical challenge to develop a suitable heteroatom-doped graphene anode. In this work, the structural and electronic influences in B-, N-, Si- and P-doped bilayer graphene (BLG) have been investigated by first-principles calculations. Pyridinic N, graphitic B and Si-doped BLG have preferential adsorption for Na with stronger surface binding than intercalation. The undoped carbon layer of B-doped BLG can be converted into n-type doping state by inserting Na, and the doped layer remains p-type mainly caused by the different electrons transfer to carbon layers from Na. Additionally, the electronic conductivity and Na diffusions on surfaces and in interlayers during sodiation are improved by doping heteroatoms. However, pyridinic N, graphitic Si and P doping promote the Na storage on surfaces and in interlayers of BLG due to the structural influence of carbon vacancy, which leads to high activation barriers during desodiation. The graphitic N-doped BLG is unsuitable and reduces the numbers of storage sites for Na in/on it. Therefore, B-doped and pyridinic N-doped BLG are promising anodes for SIBs because of stronger attraction and better kinetics of the electronic and cationic transport.

Enhancing the capacity and discharge times of flexible graphene batteries by decorating their anodes with magnetic alloys NiMnMx (Mx=Ga, In, Sn)

This work reports the electrochemical performance of flexible batteries whose graphene anodes were decorated with magnetic alloy microparticles of Ni50Mn35In15 (NiMnIn), Ni50Mn30Ga20 (NiMnGa), and Ni50Mn40Sn10 (NiMnSn). The X-ray diffraction patterns indicated that all the magnetic alloys present a martensite phase. According to the scanning electron microscopy analysis, the NiMnGa and NiMnIn microparticles presented a diameter size of 1.5–30 μm and high porosity. These anodes decorated with magnetic alloy microparticles were subjected to an acid treatment with phosphoric acid to induce the oxidation of the magnetic microparticles. As result, several oxides were simultaneously formed on their surface as confirmed by XPS and FTIR analysis. The presence of these oxides (active sites for the charge storage) enhanced the capacity, energy density and discharge times of the graphene batteries (GBs). The highest energy density (343.5 W h/kg) and capacity (621.7 mA h/g) were obtained for the GB that contained NiMnGa microparticles. In addition, all the GBs demonstrated a discharge voltage >1 V after 10 h, which suggests that they could be suitable to provide energy in portable applications.

Chemically Prelithiated Graphene for Anodes of Li-Ion Batteries

To improve the reversible capacity and electrochemical performance of the Li-ion batteries, prelithiation is one of the promising solutions as it leads to the reduction of irreversible capacity and stabilization of electrode surfaces after prelithiation. However, typical electrochemical prelithiation has drawbacks including a longer reaction period and low efficiency of the process. Here, we demonstrate a facile route for the one-pot synthesis of chemically prelithiated graphene before assembling the battery cell. In the reaction of a mixture consisting of graphene oxide (GO), lithium, and 4,4′-di-tert-butylbiphenyl (DTBP), the prelithiation and reduction of GO have occurred simultaneously by the assistance of DTBP. The prelithiated graphene exhibits improved reversible capacity (643 mAh g–1), cyclic stability (capacity retention of 87.4% after 200th cycle), and rate capability compared to those of GO and reduced graphene oxide (RGO). This chemical prelithiation method is expected to enable the efficient production of prelithiated graphene anodes for improving the performance of Li-ion batteries.

Understanding the role of graphene intercalation layers on both sides of sandwich structured graphene@MoS2@porous graphene anode in promoting sodium storage performance and stability

Developing of sodium-ion batteries (SIBs) as potential energy storage technology owns tremendous significance. However, to realize the large-scale development of SIBs, the development of high performance, high safety, low cost anode materials bears the brunt. Molybdenum disulfide (MoS2) with graphene-like layered structure is considered as one of the most promising anode materials for SIBs because of its high theoretical capacity. But MoS2 unfortunately suffers from its drastic volume variation and poor electric conductivity during the sodiation/desodiation cyclic process, which result in unsatisfied battery capacity, rate capability and cycle stability. So, exploring rational MoS2-based materials as ideal anodes is still a huge challenge. Herein, a special structure of MoS2/porous graphene composite material with high electric conductivity and high structural stability is designed. Firstly, MoS2 is grown on the surface of porous graphene, and then graphene is coated on the other side of MoS2 to obtain sandwich-like structured graphene@MoS2@porous graphene (GR@MoS2@PG) composite material. Among them, the graphene intercalation layers on both sides of MoS2 play important roles in obtaining high reversible capacity and excellent stability, because they not only can enable reversible conversion of MoS2 and provide fast electron transfer and rapid diffusion of sodium ions, but also effectively buffer the volume contraction and expansion of MoS2 during repeated sodiation/desodiation cyclic process. The GR@MoS2@PG electrode displays a high reversible capacity (260 mAh g−1 at 1 A g−1), excellent rate capability (186 mAh g−1 at 10 A g−1) and long-term cycling life (above 200 mAh g−1 at 1.0 A g−1 after 1000 cycles).

Redox-Active Vertically Aligned Mesoporous Silica Thin Films as Transparent Surfaces for Energy Storage Applications.

Organic-inorganic hybrid membranes, made of a high density of redox active moieties covalently bonded to the internal surfaces of vertically aligned mesoporous silica thin films, are relevant for applications in transparent energy storage devices. This is demonstrated here on the basis of functionalized transparent mesoporous silica thin films prepared on the indium-tin oxide electrode from the combination of an electrochemically induced self-assembly method (to generate azide-functionalized silica) and a copper-catalyzed azide-alkyne click reaction (to derivatize the material with electroactive groups). The very small thickness (105 nm) and the uniformly distributed vertical mesochannels with ultranarrow diameter (2 nm) make the hybrid film a promising substrate that not only achieves a transparency of 82% but also provides large surface area to accommodate a high density of redox active species such as ferrocene. In such rigid and insulating porous membranes, the charge transfer reactions take place through a pure electron-hopping mechanism between adjacent redox sites, which are favored by the ordered and oriented mesostructure containing large amounts of uniformly distributed ferrocene functions in the mesochannels. Their performance results from both high charge transfer rates (electron hopping) and easy mass transport (fast diffusion of counter ions). The most effective system is the ferrocene-functionalized silica film prepared from 40% organosilane, which is able to deliver a capacity of 105 C cm-3 (1.10 mC cm-2) at a current density of 0.4 A cm-3 (with up to 48% capacity retention achieved at a charging time as short as 2.8 s). Such an electrode can be associated to an electrodeposited graphene anode in a solid-state battery-capacitor hybrid device, which can deliver 0.74 mC cm-2 at a potential scan rate of 20 mV s-1. The azide-functionalized mesoporous silica film is actually a versatile platform that can be functionalized with different redox molecules, as shown here for cobaltocenium moieties, which may broaden its application field.

(Invited) Electrochemical Production of Graphene and Controlled Assembly of 3D Graphene Electrodes for Energy Storage Applications

Graphene has been intensively studied for electrode material for electrochemical energy storage devices utilizing its high electrical conductivity and high surface area. Recently introduced electrochemical exfoliation process has many advantages over conventional chemical methods, including low-cost, simple operation, fast production-rate, and in-situ functionalization. In particular, anodic electrochemical exfoliation process is one of the promising methods for fast and simple production of graphene at low cost.In this presentation, we will first discuss the detailed mechanisms of the electrochemical exfoliation process of graphite into graphene using sulfate containing electrolyte systems. We systematically monitored the structural changes in graphite and associated gas formation during the electrochemical exfoliation process, revealing that water molecules are the main source of gaseous species for the effective exfoliation of graphite into graphene. Next, we will introduce our recent efforts to fabricate 3D structured graphene anodes for Li-, Na-, K-ion batteries. Moreover, we evaluated the temperature-dependent performance of 3D graphene anodes, demonstrating their superior charge storage performance in extreme cold environments.

Irreversible Increase in Disorder in Doped Graphene Lithium Ion Battery Anodes during First Discharge

Heteroatom-doped graphene materials show high capacity as Li-ion battery anodes. However, the Li+ reduction potential in doped graphene anodes varies drastically during charging/discharging, which adversely affects battery performance. The varying reduction potential is conjectured to result from graphene sheets aggregating during electrode preparation into a disordered graphite structure, which demonstrate a similar reduction potential profile. To test this conjecture we measured the disorder during charging/discharging via in situ x-ray diffraction. We find that the doped graphene interlayer spacing irreversibly increases during the first discharge prior to solid electrolyte interphase formation, and commensurate with this phenomena we find an increase in double-layer capacitance, suggesting an increase in surface area. These results imply an increase in disorder during the first discharge, which supports the conjecture that doped graphene batteries resemble disordered graphite. However, a significant disordering occurs during the first discharge and not necessarily during electrode preparation.

The adsorption and migration behavior of divalent metals (Mg, Ca, and Zn) on pristine and defective graphene

The need for sustainable and large-scale energy supply has led to significant development of renewable energy and energy storage technologies. Divalent metal ion (Mg, Ca, and Zn) batteries are promising energy storage technologies for the sustainable energy future, but the need for suitable electrode materials have limited their commercial development. This paper investigates, at the atomic scale, the adsorption and migration of Mg, Ca, and Zn on pristine and defective graphene surfaces, to bring insight into the metal storage and mobility in graphene and carbon-based anodes for divalent metal ion batteries. Such atomistic studies can help address the challenges facing the development of novel divalent metal battery technologies, and to understand the storage differences between divalent and monovalent metal-ion batteries. The adsorption of Ca on the graphene-based system is shown to be more energetically favorable than the adsorption of both Mg and Zn, with Ca showing adsorption behavior similar to the monovalent ions (Li, Na, and K). This was further investigated in terms of metal migration on the graphene surface, with much higher migration energy barriers for Ca than for Mg and Zn on the graphene systems, leading to the trapping of Ca at defect sites to a larger extent.

Exfoliated multi-layered graphene anode with the broadened delithiation voltage plateau below 0.5 V

The commercial graphite (CG) is the conventional anode material for lithium ion batteries (LIBs) due to its low delithiation voltage plateau (below 0.5 V) and extraordinary durability. Nevertheless, the further promotion of energy density of LIBs is restricted by the limited capacity below 0.5 V of CG. Here, based on the supercritical CO 2 exfoliation technique, the production of multi-layered graphene (MLG) is achieved from the pilot scale production line. The great merit of the exfoliated MLG anode is that the voltage plateau below 0.5 V is broadened obviously as compared to those of natural graphite and CG. Additionally, no obvious lithium dendrites are observed for MLG during the lithiation process. The large delithiation capacity under the low voltage plateau of MLG is mainly benefited from the combination of Li intercalation and boundary storage mechanism, which is further confirmed by the density functional theory calculations. The LiFePO 4 /MLG full cell can afford the satisfactory electrochemical property with respect to the capacity, energy density and ultralong cycling stability (90% capacity retention after 500 cycles at 2 C), significantly better than that of LiFePO 4 /CG. Besides, this developed technique not only dedicates to producing the high-performance anode for LIBs but also opens a door for the mass production of MLG in the industrial scale. The MLG derived from the supercritical CO 2 exfoliation technique presents larger delithiation capacity below 0.5 V associated with the flat voltage plateau. The storage mechanism of MLG combines the intercalation and boundary storage models.

Highly stable multi-layered silicon-intercalated graphene anodes for lithium-ion batteries

Abstract

Impact of Surface Modification on the Lithium, Sodium, and Potassium Intercalation Efficiency and Capacity of Few-Layer Graphene Electrodes.

In a conventional lithium-ion battery (LIB), graphite forms the negative electrode or anode. Although Na is considered one of the most attractive alternatives to Li, achieving reversible Na intercalation within graphitic materials under ambient conditions remains a challenge. More efficient carbonaceous anode materials are desired for developing advanced LIBs and beyond Li-ion battery technologies. We hypothesized that two-dimensional materials with distinct surface electronic properties create conditions for ion insertion into few-layer graphene (FLG) anodes. This is because modification of the electrode/electrolyte interface potentially modifies the energetics and mechanisms of ion intercalation in the thin bulk of FLG. Through first-principles calculations; we show that the electronic, structural, and thermodynamic properties of FLG anodes can be fine-tuned by a covalent heteroatom substitution at the uppermost layer of the FLG electrode, or by interfacing FLG with a single-side fluorinated graphene or a Janus-type hydrofluorographene monolayer. When suitably interfaced with the 2D surface modifier, FLG exhibits favorable thermodynamics for the Li+, Na+, and K+ intercalation. Remarkably, the reversible binding of Na within carbon layers becomes thermodynamically allowed, and a large storage capacity can be achieved for the Na intercalated modified FLG anodes. The origin of charge-transfer promoted electronic tunability of modified FLGs is rationalized by various theoretical methods.