Preparation of graphene supported porous Si@C ternary composites and their electrochemical performance as high capacity anode materials for Li-ion batteries

Graphene supported porous Si@C ternary composites had been synthesized by various routes and their structural, morphological and electrochemical properties were investigated. Porous Si spheres coated with carbon layer and supported by graphene have been designed to form a 3D carbon conductive network. Used as anode materials for lithium ion batteries, graphene supported porous Si@C ternary composites demonstrate excellent electrochemical performance and cycling stability. The first discharge capacity is 2184.7 mA h/g at a high current density of 300 mA/g. After 50 cycles, the reversible capacity is 652.4 mA h/g at a current density of 300 mA/g and the coulomb efficiency reaches at 98.7%. Due to their excellent electrochemical properties, graphene supported porous Si@C ternary composites can be a kind of promising anode materials for lithium ion batteries.     

Porous rod-shaped Co3O4 derived from Co-MOF-74 as high-performance anode materials for lithium ion batteries

Porous rod-shaped Co₃O₄ has been successfully synthesized by one-step thermal annealing of the as-prepared Co-MOF-74 precursor and tested as anode materials for lithium ion batteries. The porous rod-shaped Co₃O₄ is found to be very attractive for lithium-ion batteries. It demonstrates a reversible capacity of 683 mAh/g after 80 cycles at 100 mA/g and an excellent rate performance with high average discharge specific capacities of 1231, 1026, 733 and 502 mAh/g at 50, 100, 200 and 400 mA/g, respectively. The excellent electrochemical performance should be due to the porous structural and composition characteristics.     

Electrospinning combined with hydrothermal synthesis and lithium storage properties of ZnFe2O4-graphene composite nanofibers

ZnFe₂O₄-graphene composite nanofibers were prepared through electrospinning technique, then with graphene oxide by the facile solvothermal method to get the final products for the first time. The obtained ZnFe₂O₄ nanofibers composed of numerous same size nanoparticles wrapped by graphene sheets to form a unique nanostructure. When the ZnFe₂O₄-graphene electrode was evaluated as anode for lithium-ion batteries, good rate capability and long-term cycling stability could be achieved. The ZnFe₂O₄-graphene electrode exhibited a first discharge capacity of 2166 mAh g⁻¹ cycling at 0.05 C, remained an average reversible capacity of 1000 mAh g⁻¹ after 50 cycles, and kept the high rate capacities of 899, 822, 760 and 711 mAh g⁻¹ at the current rates of 0.5, 1, 2 and 5 C, respectively. The excellent electrochemical performance could be ascribed to the following reasons: the large electrochemical active surface area provided by the composite nanofibers; the graphene sheets decreased the internal resistance of the lithium-ion batteries, which resulted from the electrical conductivity of the graphene sheets; the graphene sheets as conductive network could effectively restrain the agglomeration of ZnFe₂O₄ nanopaiticals.     

Microwave self-assembly of 3D graphene-carbon nanotube-nickel nanostructure for high capacity anode material in lithium ion battery

We report a microwave-assisted synthesis of a self-assembled three-dimensional graphene-carbon nanotube-nickel (3D G-CNT-Ni) nanostructure, which can be used as a high capacity anode material in lithium-ion batteries (LIBs). The unique 3D G-CNT-Ni nanostructure shows that CNTs are grown on graphene sheets through tip growth mechanism by Ni nano-particles. Bunches of CNTs and graphene sheets produce 3D network nanostructures with ultrahigh surface area, a large number of activation sites, and efficient ion pathways, all of which are crucial for high capacity anode materials in LIBs. The synthesized 3D nanostructure maintains a reversible specific capacity of 648.2 mA h/g after 50 cycles at a current density of 100 mA/g, as high capacity electrode structures in LIBs.     

Fabrication of self-binding noble metal/flexible graphene composite paper

Self-binding noble metal (Pt, Au, and Ag)/graphene composite papers as large as 13 cm in diameter were fabricated using a flow-directed method where in situ reduced graphene served as a “binder”. The papers were characterized by X-ray diffraction, scanning and transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. This approach yielded well dispersed metals with various nanostructures both on and between the graphene layers to form papers with good conductivity and flexiblility. The 300 °C-annealed Ag/graphene papers were evaluated as binder-free anodes for lithium ion batteries, delivering a reversible charge capacity of 689 mAh/g at a current density of 20 mA/g.     

Effect of graphene nanosheets on electrochemical performance of Li4Ti5O12 in lithium-ion capacitors

In order to improve the electrochemical performance of lithium titanium oxide, Li₄Ti₅O₁₂ (LTO), for the use in the lithium-ion capacitors (LICs) application, LTO/graphene composites were synthesized through a solid state reaction. The composite exhibited an interwoven structure with LTO particles dispersed into graphene nanosheets network rather than an agglomerated state pristine LTO particles. It was found that there is an optimum percentage of graphene additives for the formation of pure LTO phase during the solid state synthesis of LTO/graphene composite. The effect of graphene nanosheets addition on electrochemical performance of LTO was investigated by a systemic characterization of galvanostatic cycling in lithium and lithium-ion cell configuration. The optimized composite exhibited a decreased polarization upon cycling and delivered a specific capacity of 173 mA h g⁻¹ at 0.1 C and a well maintained capacity of 65 mA h g⁻¹ even at 20 C. The energy density of 14 Wh kg⁻¹ at a power density of 2700 W kg⁻¹ was exhibited by a LIC full cell with a balanced mass ratio of anode to cathode along with a superior capacitance retention of 97% after 3000 cycles at a current density of 0.4 A g⁻¹. This boost in reversible capacity, rate capability and cycling performance was attributed to a synergistic effect of graphene nanosheets, which provided a short lithium ion diffusion path as well as facile electron conduction channels.     

On the chemical nature of thermally reduced graphene oxide and its electrochemical Li intake capacity

Graphene oxide (GO) presents a unique chemical complexity due to the number of defect sites and chemical groups introduced by the harsh oxidative treatment. In this work, we elucidate the chemical nature of GO and thermally-reduced GO at different temperatures. These materials were characterized by a variety of techniques such as FT-IR, Raman spectroscopy, TGA, SEM, XRD, XPS, TEM, surface area, and elemental analysis. Furthermore, galvanostatic experiments demonstrate that the electrochemical performance of reduced-GOs for Li intake is optimal when GO is reduced at a relatively mild temperature of 250 °C regardless of the chemical environment. Mildly reduced-GOs show a high first cycle specific capacity of over 2000 mAh/g (charge) and 1000 mAh/g (discharge), at a large current density of 500 mA/g. After 100 cycles, the reversible capacity remains stabilized at 500 mAh/g. Our characterization results combined with density functional theory calculations suggest that the presence of specific ketone groups at the edge sites rather than their gross morphology is responsible for the enhanced performance of the material as anode electrodes.     

High-capacity graphene oxide/graphite/carbon nanotube composites for use in Li-ion battery anodes

A composite of graphene oxide sheets, carbon nanotubes (CNTs), and commercial graphite particles was prepared. The composite’s use as a high-capacity and binder-free anode material for Li-ion batteries was examined. Results showed that this novel composite had a very high reversible Li-storage capacity of 1172.5 mA h g⁻¹ at 0.5C (1C = 372 mA g⁻¹), which is thrice that of commercial graphite anode. The composite also exceeded the theoretical sum of capacities of the three ingredients. More importantly, its reversible capacity below 0.25 V can reach up to 600 mA h g⁻¹. In summary, the graphene oxide/graphite/CNT composite had higher reversible capacity, better cycling performance, and similar rate capability compared with the graphene oxide/graphite composite.     

Porous Fe2O3 nanorods anchored on nitrogen-doped graphenes and ultrathin Al2O3 coating by atomic layer deposition for long-lived lithium ion battery anode

Porous iron oxide (Fe₂O₃) nanorods anchored on nitrogen-doped graphene sheets (NGr) were synthesized by a one-step hydrothermal route. After a simple microwave treatment, the iron oxide and graphene composite (NGr-I-M) exhibits excellent electrochemical performances as an anode for lithium ion battery (LIB). A high reversible capacity of 1016 mAh g⁻¹ can be reached at 0.1 A g⁻¹. When NGr-I-M electrode was further coated by 2 ALD cycles of ultrathin Al₂O₃ film, the first cycle Coulombic efficiency (CE), rate performance and cycling stability of the coated electrode can be greatly improved. A stable capacity of 508 mAh g⁻¹ can be achieved at 2 A g⁻¹ for 200 cycles, and an impressive capacity of 249 mAh g⁻¹ at 20 A g⁻¹ can be maintained without capacity fading for 2000 cycles. The excellent electrochemical performance can be attributed to the synergy of porous iron oxide structures, nitrogen-doped graphene framework, and ultrathin Al₂O₃ film coating. These results highlight the importance of a rational design of electrode materials improving ionic and electron transports, and potential of using ALD ultrathin coatings to mitigate capacity fading for ultrafast and long-life battery electrodes.     

Control of number of graphene layers using ultrasound in supercritical CO2 and their application in lithium-ion batteries

This study reports a novel strategy using ultrasound in supercritical CO₂ for exfoliating graphite directly into single and few-layer graphene sheets. The mutually complementary characterizations of the as-exfoliated samples via atomic force microscopy, transmission electron microscopy and Raman spectroscopy indicate that the ultrasonic power greatly affects the number of layers and the lateral size of the graphene. Single-layer graphene with a lateral size of 50–100 nm and two-layer graphene with a lateral size of 0.5–10 μm are obtained using an ultrasonic power of 300 and 120 W, respectively. As-exfoliated graphene sheets heighten the electrochemical performance of LiFePO₄ cathode materials, demonstrating graphene's remarkable electrical conductivity. The specific capacity of the LiFePO₄/graphene composite cathode achieves 160 mAh/g and displays stable cycling for more than 15 cycles. This technique will enable cost-effective mass production of graphene sheets with good quality, and the as-exfoliated graphene will find wide applications, including lithium-ion batteries.     

Silver nanorods attached to graphene sheets as anode materials for lithium-ion batteries

We employed a homogenizing method to disperse silver nanorods onto graphene nanosheets (GNs) in liquid phase, forming a three-dimensional Ag/GN framework. The Ag/GN hybrid material was used to investigate Li-ion insertion/extraction properties. A microwave-assisted polyol approach was adopted to synthesize highly crystalline Ag nanorods. The as-prepared Ag/GN hybrid anode shows improved Li-storage capacity, excellent rate capability, and good cycling stability, as compared with the pure GN anode. The hybrid anode offers a reversible capacity of 1015 mA h g⁻¹ at 0.1 C and a high capacity retention of 64.1% based on the capacity ratio at 5 C–0.1C rates. The enhancement of anode performance can be attributed to an increased electrode conductivity and interlayer distance due to the insertion of metallic Ag nanorods onto a percolated GN network, thus preventing the re-stacking of graphene sheets.     

Enhanced electrochemical performance of ion-beam-treated 3D graphene aerogels for lithium ion batteries

High energy light-ion (3.8 MeV He) bombardment is used to introduce lattice defects in a 3-dimensional (3D) interconnected network of graphene aerogels (GAs). When these materials are used as anodes for lithium ion batteries, we observe improved percentage reversible capacity and cycle stability compared to those without ion-beam treatment. Furthermore, all ion-beam treated 3D graphene samples exhibit substantially higher Coulombic efficiencies, suggesting at beneficial role of vacancy-type defects in stabilizing solid-electrolyte interphases. Although 3D graphene exhibits initial reversible capacities that are 2–3 times higher than that of graphite (∼372 mAh/g), fast capacity fading is observed but becomes more stable after ion-beam treatment. Our experimental results demonstrate that ion-beam treatment is an effective route to tune and produce good-performance graphene electrodes, and that vacancy-type defects help to promote reversible lithium storage capacity in graphene. We further observe that 3D GAs irradiated to the highest dose studied (10¹⁶ cm⁻²) fail rapidly upon electrochemical cycling, likely caused by the excessive ion-beam damage and graphene restacking. Raman I(D)/I(D′) signature is considered linked to defect type in graphene and thus is proposed, for the first time, as an indicator of the reversible capacity for GAs.     

Exceptional electrochemical performance of nitrogen-doped porous carbon for lithium storage

Crumpled nitrogen-doped porous carbon sheets are successfully fabricated via chemical activation of polypyrrole-functionalized graphene sheets with KOH (APGs). The obtained APGs with nitrogen doping, high surface area, porous and crumpled structure exhibit exceptional electrochemical performances as the electrode material for LIBs, including a superhigh reversible specific capacity of 1516.2 mAh g⁻¹, excellent cycling stability over 10,000 cycles, and good rate capability (133.2 mAh g⁻¹ even at a very high current density of 40 A g⁻¹). The chemical activation synthesis strategy might open new avenues for the design of high-performance carbon-based anode materials.     

Ultrafine SnO2 nanoparticles as a high performance anode material for lithium ion battery

In this paper, the ultrafine tin oxides (SnO₂) nanoparticles are fabricated by a facile microwave hydrothermal method with the mean size of only 14 nm. Phase compositions and microstructures of the as-prepared nanoparticles have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the ultrafine SnO₂ nanoparticles are obtained to be the pure rutile-structural phase with the good dispersibility. Galvanostatic cycling and cyclic voltammetry results indicate that the first discharge capacity of the ultrafine SnO₂ electrode is 1196.63  mAh g⁻¹, and the reversible capacity could retain 272.63 mAh g⁻¹ at 100 mA g⁻¹ after 50 cycles for lithium ion batteries (LIBs). The excellent electrochemical performance of the SnO₂ anode for LIBs is attributed to its ultrafine nanostructure for providing active sites during lithium insertion/extraction processes. Pulverization and agglomeration of the active materials are effectively reduced by the microwave hydrothermal method.     

Multilayered silicon embedded porous carbon/graphene hybrid film as a high performance anode

Silicon (Si) has been regarded as one of the most attractive anode materials for the next generation lithium-ion batteries because of its large theoretical capacity, high safety, low cost and environmental benignity. However, the architecture of Si-based anode material still needs to be well designed to overcome the structure degradation and instability of the solid-electrolyte interphase caused by a large volume change during cycling. Here we report the electrochemical performances of a novel binder-free Si/carbon composite film consisting of alternatively stacked Si-porous carbon layers and graphene layers, which is synthesized by electrostatic spray deposition followed by heat treatment. For this composite film, Si nanoparticles are embedded in the porous carbon layer composed of nitrogen-doped carbon framework, carbon black and carbon nanotubes. And the combined Si-porous carbon layer is further sandwiched by flexible and conductive graphene sheets. The multilayered Si-porous carbon/graphene electrode shows a maximum reversible capacity of 1020 mAh g⁻¹ with 75% capacity retention after 100 cycles and a good rate capability on the basis of the total electrode weight. The excellent electrochemical performances are attributed to the fact that the layer-by-layer porous carbon matrix can accommodate the volume change of Si particles and maintain the structural and electrical integrities.     

MoO3/reduced graphene oxide composites as anode material for sodium ion batteries

MoO₃/reduced graphene oxide (MoO₃/RGO) composites were successfully prepared via a facile one-step hydrothermal method, and evaluated as anode materials for sodium ion batteries (SIBs). The crystal structures, morphologies and electrochemical properties of the as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge tests, respectively. The results show that the introduction of RGO can enhance the electrochemical performances of MoO₃/RGO composites. MoO₃/RGO composite with 6 wt% RGO delivers the highest reversible capacity of ~208 mA h g⁻¹ at 50 mA g⁻¹ after 50 cycles with good cycling stability and excellent rate performance for SIBs. The excellent sodium storage performance of MoO₃/RGO should be attributed to the synergistic effect between MoO₃ and RGO, which offers the increased electrical conductivity, the facilitated electron transfer ability and the buffering of volume expansion.     

One-pot synthesis of uniform Fe3O4 nanocrystals encapsulated in interconnected carbon nanospheres for superior lithium storage capability

Uniform and small Fe₃O₄ nanocrystals (∼9 nm) encapsulated in interconnected carbon nanospheres (∼60 nm) for a high-rate Li-ion battery anode have been fabricated by a one-step hydrothermal process followed by annealing under Ar, which can be applied for the preparation of a number of metal oxide nanocrystals encapsulated in interconnected carbon nanospheres. The as-synthesized interconnected Fe₃O₄@C nanospheres displayed high performance as an anode material for Li-ion battery, such as high reversible lithium storage capacity (784 mA h/g at 1 C after 50 cycles), high Coulombic efficiency (∼99%), excellent cycling stability, and superior rate capability (568 mA h/g at 5 C and 379 mA h/g at 10 C) by virtue of their unique structure: the nanosized Fe₃O₄ nanocrystals encapsulated in interconnected conductive carbon nanospheres not only endow large quantity of accessible active sites for lithium ion insertion as well as good conductivity and short diffusion length for lithium ion transport but also can effectively circumvent the volume expansion/contraction associated with lithium insertion/extraction.     

Graphene nanosheets based on controlled exfoliation process for enhanced lithium storage in lithium-ion battery

A facile and rapid approach was used for the fabrication of chemically derived graphene nanosheets based on the reduction of graphite oxide (GO) in tube furnace assembly at different temperatures. The morphologies, microstructures, specific surface areas and other features of GO and graphene nanosheets were characterized. Structure characterization indicates that the platelet thickness of graphene nanosheets obtained at 300 °C was 1.62 nm, which corresponds to an approximately 5 layers stacking of the monoatomic graphene nanosheets. Electrochemical performances of the as-prepared graphene nanosheets were performed, the result of which could prove the above observation that graphene nanosheets (5 layers) obtained at 300 °C actually displayed the most remarkable electrochemical performances: the first discharge and charge capacities of graphene nanosheets were as high as 2137 mAh/g and 994 mAh/g, respectively, and after 100 cycles graphene nanosheets still possessed a high capacity of 478 mAh/g.     

Growth of titania and tin oxide from Ti2SnC via rapid thermal oxidation in air for lithium-ion battery application

Herein, we report the synthesis of TiO₂–SnO₂–C/carbide hybrid electrode materials for Li-ion batteries (LIBs) via two different methods of controlled oxidation of layered Ti₂SnC. The material was partially oxidized in an open-air furnace (OAF) or using a rapid thermal annealing (RTA) approach to obtain the desired TiO₂–SnO₂–C/carbide hybrid material; the carbide phase encompassed both residual Ti₂SnC and TiC as a reaction product. We tested the oxidized materials as an anode in a half cell to investigate their electrochemical performance in LIBs. Analysis of the various oxidation conditions indicated the highest initial lithiation capacity of 838 mAh/g at 100 mA/g for the sample oxidized in the OAF at 700°C for 1 h. Still, the delithiation capacity dropped to 427 mAh/g and faded over cycling. Long-term cycling demonstrated that the RTA sample treated at 800°C for 30 s was the most efficient, as it demonstrated a reversible capacity of around 270 mAh/g after 150 cycles, as well as a specific capacity of about 150 mAh/g under high cycling rate (2000 mA/g). Given the materials’ promising performance, this processing method could likely be applied to many other members of the MAX family, with a wide range of energy storage applications.     

Improving electrochemical properties of LiCoO2 by enhancing thermal decomposition of Cobalt and Lithium carbonates to synthesize ultrafine powders

Ultrafine LiCoO₂ powders were directly synthesized by enhancing thermal decomposition of Cobalt and Lithium carbonates through a mechanochemical activation treatment to intensify the solid state diffusion reaction. Effects of activation treatment time on particle size and structure of the LiCoO₂ compound were investigated. In the present study, the optimum mechano-chemical activation time was found to be 10 h. In this study, the ultrafine LiCoO₂ powders (particle size in the range from 200 nm to 400 nm) show good structural stability and higher structural integrity. X-ray photoelectron spectroscopy (XPS) results indicate that most of Co cations exist as Co³⁺, which contributes to the improvement of the electrochemical performance. Cyclic voltammetry (CV) curves of different cycles display almost a complete overlap, which can be regarded as another evidence of the excellent cycle performance. The LiCoO₂ powders exhibit a high initial discharge specific capacity of 175.2 mAh/g at 0.1 C (274 mA/g at 1 C) and a remarkable cycle stability from 167.5 mAh/g to 146.2 mAh/g at 0.5 C and from 147.5 mAh/g to 115.2 mAh/g at 3 C after 100 cycles in the range of 3.3–4.3 V. The apparent activation energy and the frequency factor of the decomposition of CoCO₃ are 69.83 kJ/mol and 1.369×10⁶, respectively, indicating that the ultrafine in-process product of Co₃O₄ can be quickly prepared at a low temperature.