Electrochemical Properties of Tin Oxide Flake/Reduced Graphene Oxide/Carbon Composite Powders as Anode Materials for Lithium‐Ion Batteries

Hierarchically structured tin oxide/reduced graphene oxide (RGO)/carbon composite powders are prepared through a one‐pot spray pyrolysis process. SnO nanoflakes of several hundred nanometers in diameter and a few nanometers in thickness are uniformly distributed over the micrometer‐sized spherical powder particles. The initial discharge and charge capacities of the tin oxide/RGO/carbon composite powders at a current density of 1000 mA g^?1 are 1543 and 1060 mA h g^?1, respectively. The discharge capacity of the tin oxide/RGO/carbon composite powders after 175 cycles is 844 mA h g^?1, and the capacity retention measured from the second cycle is 80 %. The transformation during cycling of SnO nanoflakes, uniformly dispersed in the tin oxide/RGO/carbon composite powder, into ultrafine nanocrystals results in hollow nanovoids that act as buffers for the large volume changes that occur during cycling, thereby improving the cycling and rate performances of the tin oxide/RGO/carbon composite powders.     

Sodium‐Ion Storage Properties of FeS–Reduced Graphene Oxide Composite Powder with a Crumpled Structure

The sodium‐ion storage properties of FeS–reduced graphene oxide (rGO) and Fe₃O₄‐rGO composite powders with crumpled structures have been studied. The Fe₃O₄‐rGO composite powder, prepared by one‐pot spray pyrolysis, could be transformed to an FeS‐rGO composite powder through a simple sulfidation treatment. The mean size of the Fe₃O₄ nanocrystals in the Fe₃O₄‐rGO composite powder was 4.4 nm. After sulfidation, FeS nanocrystals of size several hundred nanometers were confined within the crumpled structure of the rGO matrix. The initial discharge capacities of the FeS‐rGO and Fe₃O₄‐rGO composite powders were 740 and 442 mA h g^?1, and their initial charge capacities were 530 and 165 mA h g^?1, respectively. The discharge capacities of the FeS‐rGO and Fe₃O₄‐rGO composite powders at the 50th cycle were 547 and 150 mA h g^?1, respectively. The FeS‐rGO composite powder showed superior sodium‐ion storage performance compared to the Fe₃O₄‐rGO composite powder.     

Superior Lithium‐Ion Storage Properties of Mesoporous CuO–Reduced Graphene Oxide Composite Powder Prepared by a Two‐Step Spray‐Drying Process

Mesoporous CuO–reduced graphene oxide (rGO) composite powders were prepared by using a two‐step spray‐drying process. In the first step, hollow CuO powders were prepared from a spray solution of copper nitrate trihydrate with citric acid and were wet milled to obtain a colloidal spray solution. In the second step, spray drying of the colloidal solution that contained dispersed GO nanosheets produced mesoporous CuO–rGO composite powders with particle sizes of several microns. Thermal reduction of GO nanosheets to rGO nanosheets occurred during post‐treatment at 300 °C. Initial discharge capacities of the hollow CuO, bare CuO aggregate, and CuO–rGO composite powders at a current density of 2 A g^?1 were 838, 1145, and 1238 mA h g^?1, respectively. Their discharge capacities after 200 cycles were 259, 380, and 676 mA h g^?1, respectively, and their corresponding capacity retentions measured from the second cycle were 67, 48, and 76 %, respectively. The mesoporous CuO–rGO composite powders have high structural stability and high conductivity because of the rGO nanosheets, and display good cycling and rate performances.     

One‐Pot Synthesis of Carbon‐Coated Nanostructured Iron Oxide on Few‐Layer Graphene for Lithium‐Ion Batteries

Nanostructure engineering has been demonstrated to improve the electrochemical performance of iron oxide based electrodes in Li‐ion batteries (LIBs). However, the synthesis of advanced functional materials often requires multiple steps. Herein, we present a facile one‐pot synthesis of carbon‐coated nanostructured iron oxide on few‐layer graphene through high‐pressure pyrolysis of ferrocene in the presence of pristine graphene. The ferrocene precursor supplies both iron and carbon to form the carbon‐coated iron oxide, while the graphene acts as a high‐surface‐area anchor to achieve small metal oxide nanoparticles. When evaluated as a negative‐electrode material for LIBs, our composite showed improved electrochemical performance compared to commercial iron oxide nanopowders, especially at fast charge/discharge rates.     

Electrochemical Properties of Fiber‐in‐Tube‐ and Filled‐Structured TiO2 Nanofiber Anode Materials for Lithium‐Ion Batteries

Phase‐pure anatase TiO₂ nanofibers with a fiber‐in‐tube structure were prepared by the electrospinning process. The burning of titanium‐oxide‐carbon composite nanofibers with a filled structure formed as an intermediate product under an oxygen atmosphere produced carbon‐free TiO₂ nanofibers with a fiber‐in‐tube structure. The sizes of the nanofiber core and hollow nanotube were 140 and 500 nm, respectively. The heat treatment of the electrospun nanofibers at 450 and 500 °C under an air atmosphere produced grey and white filled‐structured TiO₂ nanofibers, respectively. The initial discharge capacities of the TiO₂ nanofibers with the fiber‐in‐tube and filled structures and the commercial TiO₂ nanopowders were 231, 134, and 223 mA h g^?1, respectively, and their corresponding charge capacities were 170, 100, and 169 mA h g^?1, respectively. The 1000th discharge capacities of the TiO₂ nanofibers with the fiber‐in‐tube and filled structures and the commercial TiO₂ nanopowders were 177, 64, and 101 mA h g^?1, respectively, and their capacity retentions measured from the second cycle were 89, 82, and 52 %, respectively. The TiO₂ nanofibers with the fiber‐in‐tube structure exhibited low charge transfer resistance and structural stability during cycling and better cycling and rate performances than the TiO₂ nanofibers with filled structures and the commercial TiO₂ nanopowders.     

Superior Electrochemical Performance of Sulfur/Graphene Nanocomposite Material for High‐Capacity Lithium–Sulfur Batteries

Sulfur/graphene nanocomposite material has been prepared by incorporating sulfur into the graphene frameworks through a melting process. Field‐emission scanning electron microscope analysis shows a homogeneous distribution of sulfur in the graphene nanosheet matrix. The sulfur/graphene nanocomposite exhibits a super‐high lithium‐storage capacity of 1580 mAh g^?1 and a satisfactory cycling performance in lithium–sulfur cells. The enhancement of the reversible capacity and cycle life could be attributed to the flexible graphene nanosheet matrix, which acts as a conducting medium and a physical buffer to cushion the volume change of sulfur during the lithiation and delithiation process. Graphene‐based nanocomposites can significantly improve the electrochemical performance of lithium–sulfur batteries.     

Facile Mechanochemical Synthesis of Nano SnO2/Graphene Composite from Coarse Metallic Sn and Graphite Oxide: An Outstanding Anode Material for Lithium‐Ion Batteries

A facile method for the large‐scale synthesis of SnO₂ nanocrystal/graphene composites by using coarse metallic Sn particles and cheap graphite oxide (GO) as raw materials is demonstrated. This method uses simple ball milling to realize a mechanochemical reaction between Sn particles and GO. After the reaction, the initial coarse Sn particles with sizes of 3–30 μm are converted to SnO₂ nanocrystals (approximately 4 nm) while GO is reduced to graphene. Composite with different grinding times (1 h 20 min, 2 h 20 min or 8 h 20 min, abbreviated to 1, 2 or 8 h below) and raw material ratios (Sn:GO, 1:2, 1:1, 2:1, w/w) are investigated by X‐ray diffraction, X‐ray photoelectron spectroscopy, field‐emission scanning electron microscopy and transmission electron microscopy. The as‐prepared SnO₂/graphene composite with a grinding time of 8 h and raw material ratio of 1:1 forms micrometer‐sized architected chips composed of composite sheets, and demonstrates a high tap density of 1.53 g cm^?3. By using such composites as anode material for LIBs, a high specific capacity of 891 mA h g^?1 is achieved even after 50 cycles at 100 mA g^?1.     

Superior Electrochemical Properties of Nanofibers Composed of Hollow CoFe2O4 Nanospheres Covered with Onion‐Like Graphitic Carbon

Nanofibers composed of hollow CoFe₂O₄ nanospheres covered with onion‐like carbon are prepared by applying nanoscale Kirkendall diffusion to the electrospinning process. Amorphous carbon nanofibers embedded with CoFe₂@onion‐like carbon nanospheres are prepared by reduction of the electrospun nanofibers. Oxidation of the CoFe₂‐C nanofibers at 300 °C under a normal atmosphere produces porous nanofibers composed of hollow CoFe₂O₄ nanospheres covered with onion‐like carbon. CoFe₂ nanocrystals are transformed into the hollow CoFe₂O₄ nanospheres during oxidation through a well‐known nanoscale Kirkendall diffusion process. The discharge capacities of the carbon‐free CoFe₂O₄ nanofibers composed of hollow nanospheres and the nanofibers composed of hollow CoFe₂O₄ nanospheres covered with onion‐like carbon are 340 and 930 mA h g^?1, respectively, for the 1000th cycle at a current density of 1 A g^?1. The nanofibers composed of hollow CoFe₂O₄ nanospheres covered with onion‐like carbon exhibit an excellent rate performance even in the absence of conductive materials.     

Reduced Graphene Oxide‐Supported TiO2 Fiber Bundles with Mesostructures as Anode Materials for Lithium‐Ion Batteries

Although the synthesis of mesoporous materials is well established, the preparation of TiO₂ fiber bundles with mesostructures, highly crystalline walls, and good thermal stability on the RGO nanosheets remains a challenge. Herein, a low‐cost and environmentally friendly hydrothermal route for the synthesis of RGO nanosheet‐supported anatase TiO₂ fiber bundles with dense mesostructures is used. These mesostructured TiO₂‐RGO materials are used for investigation of Li‐ion insertion properties, which show a reversible capacity of 235 mA h g^?1 at 200 mA g^?1 and 150 mA h g^?1 at 1000 mA g^?1 after 1000 cycles. The higher specific surface area of the new mesostructures and high conductive substrate (RGO nanosheets) result in excellent lithium storage performance, high‐rate performance, and strong cycling stability of the TiO₂‐RGO composites.     

Electrochemical Properties of Yolk–Shell‐Structured Zn–Fe–S Multicomponent Sulfide Materials with a 1:2 Zn/Fe Molar Ratio

Yolk–shell‐structured Zn–Fe–S multicomponent sulfide materials with a 1:2 Zn/Fe molar ratio were prepared applying a sulfidation process to ZnFe₂O₄ yolk–shell powders. The Zn–Fe–S powders had mixed sphalerite (Zn,Fe)S and hexagonal FeS crystal structures. The discharge capacities of the Zn–Fe–S powders sulfidated at 350 °C at a constant current density of 500 mA g^?1 for the first, second, and fiftieth cycles were 1098, 912, and 913 mA h g^?1, respectively. The powders exhibited a high discharge capacity of 602 mA h g^?1 even at the high current density of 10 A g^?1. The synergistic effect of yolk–shell structure and multicomponent composition improved the electrochemical properties of Zn–Fe–S powders.     

One‐Pot Synthesis of CoSex–rGO Composite Powders by Spray Pyrolysis and Their Application as Anode Material for Sodium‐Ion Batteries

A simple one‐pot synthesis of metal selenide/reduced graphene oxide (rGO) composite powders for application as anode materials in sodium‐ion batteries was developed. The detailed mechanism of formation of the CoSe_x–rGO composite powders that were selected as the first target material in the spray pyrolysis process was studied. The crumple‐structured CoSe_x–rGO composite powders prepared by spray pyrolysis at 800 °C had a crystal structure consisting mainly of Co_0.85Se with a minor phase of CoSe₂. The bare CoSe_x powders prepared for comparison had a spherical shape and hollow structure. The discharge capacities of the CoSe_x–rGO composite and bare CoSe_x powders in the 50th cycle at a constant current density of 0.3 A g^?1 were 420 and 215 mA h g^?1, respectively, and their capacity retentions measured from the second cycle were 80 and 46 %, respectively. The high structural stability of the CoSe_x–rGO composite powders for repeated sodium‐ion charge and discharge processes resulted in superior sodium‐ion storage properties compared to those of the bare CoSe_x powders.     

Superior Lithium‐Ion Storage Properties of Si‐Based Composite Powders with Unique Si@Carbon@Void@Graphene Configuration

Composite powders of the configuration Si@carbon@void@graphene were prepared by a one‐step spray pyrolysis process, by adding polyvinylpyrrolidone (PVP) to a precursor solution containing graphene oxide (GO) sheets and silicon nanoparticles (NPs). Morphological analysis indicates that the individual Si NPs are coated with amorphous carbon and encapsulated in a micrometer‐sized graphene ball structure that offers a large amount of buffer space. The addition of PVP improves the stability of the colloidal spray solution containing the GO sheets and the Si NPs. Consequently, the prepared Si@C@void@graphene composite powders have a relatively more uniform morphology than the Si@void@graphene composite powders prepared from the spray solution without PVP. The first charge and discharge capacities of the Si@C@void@graphene electrode measured at 0.1 A g^?1 are as high as 3102 and 2215 mA h g^?1, respectively. With an increase in the current rate from 0.5 to 11 A g^?1, 46 % of the original capacity (i.e., 2134 mA h g^?1) is maintained. After 500 cycles at a high rate of 7 A g^?1, the Si@C@void@graphene electrode shows 84 % capacity retention and 99.8 % of the average Coulombic efficiency. The superior cycling and rate capabilities of the prepared Si@C@void@graphene electrode could be attributed to the uniform carbon coating of the Si NPs and the graphene ball structure, which facilitates efficient diffusion of Li ions and prevents the penetration of electrolyte into graphene ball during cycling.     

Mesoporous Nickel Oxide Nanowires: Hydrothermal Synthesis,Characterisation and Applications for Lithium‐Ion Batteries and Supercapacitors with Superior Performance

Mesoporous nickel oxide nanowires were synthesized by a hydrothermal reaction and subsequent annealing at 400 °C. The porous one‐dimensional nanostructures were analysed by field‐emission SEM, high‐resolution TEM and N₂ adsorption/desorption isotherm measurements. When applied as the anode material in lithium‐ion batteries, the as‐prepared mesoporous nickel oxide nanowires demonstrated outstanding electrochemical performance with high lithium storage capacity, satisfactory cyclability and an excellent rate capacity. They also exhibited a high specific capacitance of 348 F g^?1 as electrodes in supercapacitors.     

Flame Spray Pyrolysis for Finding Multicomponent Nanomaterials with Superior Electrochemical Properties in the CoOx‐FeOx System for Use in Lithium‐Ion Batteries

High‐temperature flame spray pyrolysis is employed for finding highly efficient nanomaterials for use in lithium‐ion batteries. CoO_x‐FeO_x nanopowders with various compositions are prepared by one‐pot high‐temperature flame spray pyrolysis. The Co and Fe components are uniformly distributed over the CoO_x‐FeO_x composite powders, irrespective of the Co/Fe mole ratio. The Co‐rich CoO_x‐FeO_x composite powders with Co/Fe mole ratios of 3:1 and 2:1 have mixed crystal structures with CoFe₂O₄ and Co₃O₄ phases. However, Co‐substituted magnetite composite powders prepared from spray solutions with Co and Fe components in mole ratios of 1:3, 1:2, and 1:1 have a single phase. Multicomponent CoO_x‐FeO_x powders with a Co/Fe mole ratio of 2:1 and a mixed crystal structure with Co₃O₄ and CoFe₂O₄ phases show high initial capacities and good cycling performance. The stable reversible discharge capacities of the composite powders with a Co/Fe mole ratio of 2:1 decrease from 1165 to 820 mA h g^?1 as the current density is increased from 500 to 5000 mA g^?1; however, the discharge capacity again increases to 1310 mA h g^?1 as the current density is restored to 500 mA g^?1.     

Three‐Dimensional Hierarchical Constructs of MOF‐on‐Reduced Graphene Oxide for Lithium–Sulfur Batteries

A three‐dimensional (3D) hierarchical MOF‐on‐reduced graphene oxide (MOF‐on‐rGO) compartment was successfully synthesized through an in situ reduced and combined process. The unique properties of the MOF‐on‐rGO compartment combining the polarity and porous features of MOFs with the high conductivity of rGO make it an ideal candidate as a sulfur host in lithium–sulfur (Li‐S) batteries. A high initial discharge capacity of 1250 mAh g^?1 at a current density of 0.1 C (1.0 C=1675 mAh g^?1) was reached using the MOF‐on‐rGO based electrode. At the rate of 1.0 C, a high specific capacity of 601 mAh g^?1 was still maintained after 400 discharge–charge cycles, which could be ascribed to the synergistic effect between MOFs and rGO. Both the hierarchical structures of rGO and the polar pore environment of MOF retard the diffusion and migration of soluble polysulfide, contributing to a stable cycling performance. Moreover, the spongy‐layered rGO can buffer the volume expansion and contraction changes, thus supplying stable structures for Li‐S batteries.     

Flexible Magnetic Nanoparticles–Reduced Graphene Oxide Composite Membranes Formed by Self‐Assembly in Solution

A facile and robust route for the pre‐synthesized Fe₃O₄ nanoparticles (NPs) exclusively assembled on both sides of reduced graphene oxide (RGO) sheets with tunable density forming two‐dimensional NPs composite membranes is developed in solution. The assembly is driven by electrostatic attraction, and the nanocomposite sheets display considerable mechanical robustness, such as it can sustain supersonic and solvothermal treatments without NPs falling off, also, can freely float in solution and curl into a tube. The obtained two‐dimensional composite grain membranes exhibit superparamagnetic behavior at room temperature but responds astutely to an external magnetic field. In addition, these magnetic composite membranes show an enhanced absorption capability for microwaves. The grain sheets are attractive for biomedical, sensors, environmental applications and electric‐magnetic devices benefited from large surfaces, high magnetization moment, and superparamagnetic properties. The effective integration of oxide nanocrystals on RGO sheets provides a new way to design semiconductor–carbon nanocomposites for nanodevices or catalytic applications.     

Solvated Graphene Frameworks as High‐Performance Anodes for Lithium‐Ion Batteries

A solvent‐exchange approach for the preparation of solvated graphene frameworks as high‐performance anode materials for lithium‐ion batteries is reported. The mechanically strong graphene frameworks exhibit unique hierarchical solvated porous networks and can be directly used as electrodes with a significantly improved electrochemical performance compared to unsolvated graphene frameworks, including very high reversible capacities, excellent rate capabilities, and superior cycling stabilities.     

Cobalt–Manganese Mixed‐Sulfide Nanocages Encapsulated by Reduced Graphene Oxide: In Situ Sacrificial Template Synthesis and Superior Lithium Storage Properties

This work demonstrates a facile in situ synthesis of cobalt–manganese mixed sulfide (CoMn‐S) nanocages on reduced graphene oxide (RGO) sheets by using a crystalline Co–Mn precursor as the sacrificial template. The CoMn‐S/RGO hybrid was applied as the anode for Li‐ion storage and exhibited superior specific capacity, excellent cycling performance, and great rate capability. In particular, lithium storage testing revealed that the hybrid delivered high discharge–charge capacities of 670 mA h g⁻¹ at 1.0 A g⁻¹ after 400 cycles and 925 mA h g⁻¹ at 0.1 A g⁻¹ after 300 cycles. The outstanding electrochemical performance of CoMn‐S/RGO is attributed to the close entanglement of nanocages with RGO nanosheets achieved by the synthetic method, which greatly improves ion/electron transport along the interfaces and efficiently mitigates volume dilation during lithium reactions. This rational design of both the composition and architecture of mixed metal sulfides can be expanded to other composite systems for high‐capacity Li‐ion batteries and provides a unique insight into the development of advanced hybrid electrode materials.     

Synthesis of Mesoporous Wall‐Structured TiO2 on Reduced Graphene Oxide Nanosheets with High Rate Performance for Lithium‐Ion Batteries

Mesoporous wall‐structured TiO₂ on reduced graphene oxide (RGO) nanosheets were successfully fabricated through a simple hydrothermal process without any surfactants and annealed at 400 °C for 2 h under argon. The obtained mesoporous structured TiO₂–RGO composites had a high surface area (99 0307 m² g^?1) and exhibited excellent electrochemical cycling (a reversible capacity of 260 mAh g^?1 at 1.2 C and 180 mAh g^?1 at 5 C after 400 cycles), demonstrating it to be a promising method for the development of high‐performance Li‐ion batteries.