•Monolithic SiO2/GO composite aerogel was prepared.•Thermal insulation performance of composite aerogels was improved.•The mechanical strength of composite aerogels was enhanced.In order to improve the thermal insulation and mechanical property of silica (SiO2) aerogels, the graphene oxide (GO), as nanofillers, was added into SiO2 matrix to prepare the SiO2/GO composite aerogel monoliths on the basis of sol-gel technology and submitted to supercritical drying. The results showed that the monoliths were maintained and GO was well-distributed in the aerogel, due to the interfacial interaction between GO nanosheets and SiO2 matrix. The thermal insulation property of composite aerogels was improved in contrast with that of pure aerogel. The experimental results suggested that the thermal conductivity was lowered from 0.0089 W/mK to 0.0072 W/mK. A possible mechanism was analyzed to explain this result in virtue of GO loadings. The mechanical strength of aerogels was enhanced. It was found that with the loading of GO from 0.0 wt% to 5.0 wt%, the compressive modulus was enhanced from 0.238 MPa to 0.394 MPa, which was a significant improvement for low-solid-content silica aerogels. Moreover, the composite aerogels exhibited some toughness compared to the fragility of pure aerogel.

In this work, the triblock copolymer F127 has been used as the carbon precursor to fabricate carbon nanosheets (CNSs) by a sodium chloride surface-assisted bottom-up strategy. The CNSs possess a thickness of about 6 nm and an oxygen content of 15.6 at%. As an anode for lithium-ion batteries, CNSs exhibit reversible capacities of 830 mA h g−1 after 500 cycles at 1 A g−1 and 240 mA h g−1 at 20 A g−1, which is among the best of the reported lithium storage performances of carbon materials. When used as an anode material in sodium-ion batteries, the CNS electrode exhibits a reversible capacity of 367 mA h g−1 at 50 mA g−1 after 60 cycles and still delivers 112 mA h g−1 at 20 A g−1. The high reversible capacity and excellent rate performance would be ascribed to the synergistic effect of the 2D structure, defects, and expanded crystallites. This work extends the sodium chloride template method to prepare thin CNSs by using a suitable carbon precursor and provides some insights into the relationship between the structure of CNSs and the electrochemical performance.

•A series of hierarchical porous carbon nanosheets (HPCNs) are prepared by a template strategy using coal-based graphene quantum dots (GQDs) as the building blocks.•The unique interconnected loose-stacking graphene-like structure of the HPCNs endows their high specific surface area, hierarchical pore distribution, excellent conductivity, abundant surface active sites, and sufficient ion migration channels.•Under the optimized conditions, the HPCN shows a high specific capacitance of 230 F g−1 and at the current density of 1 A g−1 with the capacity retention of 170 F g−1 at 100 A g−1 as well as excellent endurability.Using coal-based graphene quantum dots (GQDs) as the building blocks, we develop a simple template-assisted assembly strategy to prepare hierarchical porous carbon nanosheets (HPCNs) for supercapacitor electrodes. The coal-based GQDs are prepared by a simple liquid phase oxidation of the bituminous coal. Benefiting from their small size, enriched edge structure, abundant functional groups, and good flexibility and chemical reactivity, these GQDs are suitable to construct complex nanoarchitectures for advanced energy storage materials. As a result, the HPCNs show an interconnected loose-stacking graphene-like structure with the specific surface area of 1332 m2 g−1, hierarchical pore distribution, excellent conductivity, abundant active sites, and sufficient ion migration channels. An in situ chemical activation is further applied to improve its energy storage performance. Under the optimized conditions, the activated HPCN with a specific surface area of 1450 m2 g−1 shows a greatly improved capacitive performance, with a high specific capacitance of 230 F g−1 (1 A g−1) and capacitance retention of 74% at 100 A g−1 (170 F g−1). No obvious capacity fade was found even after cycled at 10 A g−1 for 10,000 times, demonstrating their excellent endurability. Our work may provide new thought for the effective use of abundant coal resource to design and preparation advanced carbon nanoarchitectures for energy storage.Download high-res image (438KB)Download full-size image

•Chrysanthemum-like C/FeS microspheres are synthesized by one-step solvothermal method.•FeS nanosheets and carbon nanosheets are with 2D sheet-on-sheet structure.•2D C/FeS nanosheets are self-assembled to form a 3D chrysanthemum-like morphology.•The microspheres show excellent sodium-storage performance of 500 mAh g−1 at 0.2 A g−1.Chrysanthemum-like carbon/FeS microspheres (CL-C/FeS) are prepared from a one-step solvothermal method. The morphology and structure of the CL-C/FeS are characterized by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscope. We note that the prepared CL-C/FeS microspheres exhibit the average diameter of 15 μm and possess a sheet-on-sheet structure. FeS nanosheets are stacked on the carbon sheets to form a 2D sheet-on-sheet structure, these 2D C/FeS nanosheets are self-assembled to form a 3D chrysanthemum-like morphology. Due to the unique structure, CL-C/FeS microspheres show the excellent sodium-storage performance of 500 mAh g−1 at 0.2 A g−1 and 260 mAh g−1 at 1 A g−1, which are higher than those of most reported values. Therefore, the CL-C/FeS with appropriate structure is expected to be a competitive choice for anode materials for sodium ion batteries.

Silica aerogel is deemed as a kind of high-performance thermal insulation materials. However, the existence of macropores in the structure is always ignored in the research and application of aerogels. Thus the thermal insulation performance of silica aerogels could be further improved if the macropores are reduced. In this work, nano-sized Al2O3 powders are explored as nano fillers to reduce the macropore volume fraction in silica aerogels by filling the big voids among the silica aggregates, and further lower the thermal conductivity. The experimental results showed that the macropore volume fraction (VMAC) was dramatically reduced from 63.05% to 23.12% with the addition of Al2O3 powders ranging from 0.0 g to 1.0 g. This trend was also verified by the variation of (VT*-VBET) and (VBET/VT*). Accordingly, the thermal insulation performance was improved due to the reduction of macropores in aerogels. The lowest thermal conductivity of Al2O3-doped aerogels reached 7.41 mW/(m K) in contrast with that of pure silica aerogels (9.00 mW/(m K)), which was a significant decline for aerogel-based materials due to the gaseous heat transfer being further weakened. Moreover, the increment of thermal conductivity from 7.41 to 9.71 mW/(m K) with the Al2O3 powders increasing could be attributed to the enhancement of solid heat transfer in the system. The variation of experimental thermal conductivity was in good agreement with the result of theoretical calculation. This study proposed an innovative idea to improve the thermal insulation of aerogel under ambient conditions.

Hierarchical porous carbon microspheres (HPCMs) have been fabricated by an impregnation-carbonization method using MgAl-layered double oxides (LDOs) microspheres as templates and sucrose as carbon source. The MgAl-LDOs microspheres templates are obtained via stacking and self-assembly of MgAl-layered double hydroxides particles in high-temperature calcination. The abundant hierarchical porous structure provides not only fast transport channels for ion diffusion but also facile access for non-aqueous electrolyte. Owing to the unique spherical structure, the prepared HPCMs possess the tap density of 0.825 g mL−1, the gravimetric capacities of 1140.5, 650.3, and 347.9 mA h g−1 and volumetric capacities of 940.9, 536.5 and 287.0 mA h cm−3 at the current densities of 0.05, 0.2, and 1 A g−1, respectively, when used as the anode for lithium ion batteries. This work presents a new strategy to prepare carbon microspheres, and the material with high specific capacity and good rate performance exhibits good prospect in lithium ion batteries.Download high-res image (377KB)Download full-size image

For improving the capacity and stability of Sn-based anode materials, a novel Sn–Co nanoalloy embedded in porous N-doped carbon was synthesized using the metal–organic framework ZIF-67 as both the template and carbon source, and SnCl4 as the tin source through carbonization. This composite shows the shape of a microbox with the diameter of about 2 μm in which about 10 nm of Sn–Co nanoalloy particles were uniformly embedded. When used as the anode material for lithium-ion batteries, it exhibits a high capacity of 945 mA h g−1, and 86.6% capacity retention after 100 cycles at 100 mA g−1 as well as an excellent rate capacity of 472 mA h g−1 at a high current density of 2 A g−1. The superior electrochemical performance can be ascribed to the well-dispersed, nano-sized alloy and the buffering effect of porous N-doped carbon coating. Moreover, the uniform particles remain intact upon cycling which gives the material enhanced electrochemical stability.

The optional molecular structures and compositions have made metal–organic frameworks (MOFs) an important precursor for preparing functional nanomaterials. In this paper, ZnO nanosheets growing on a MOF-derived porous carbon matrix (ZnO/MPC) were synthesized by in situ pyrolysis of a Zn-based mixed-ligand MOF. The formation of ZnO nanosheets relies on the intermediate structures of the pyrolytic MOFs. The inherent molecular structure and the escape of the ligand molecules will induce the formation of a stacked structure during the heat treatment process, and the layered spaces can provide a directional path for the motion of Zn atoms to the surface of carbon bulk during the pyrolysis of the precursor. This work shows that one can design and synthesize novel nanostructures by controlling the intermediate structures of MOF precursors during the pyrolysis process. The as-synthesized ZnO/MPC also displayed an excellent cyclability and a high reversible capacity of 920 mA h g−1 at a current density of 60 mA g−1, exhibiting a promising prospect in lithium storage application.

•Thermal treatment was applied to lower the macropore fraction in aerogels.•Theoretical calculation was used to evaluate the experimental results.•This study provided a strategy to improve the thermal insulation performance of aerogels.In this work, thermal treatment to the as-prepared silica aerogels was explored as a strategy to reduce the macropores in aerogels, thus to improve the thermal insulation performance. The experimental results show that the pore size exhibits a slight shift to the value lower than the pore size of no-heat-treated silica aerogels and the macropore volume fraction experiences sharp decline from 63.05 to 24.82% after thermal treatment at 800 °C. The thermal conductivity doesn't increase with the enhancement of density but decreases from 0.0090 W/(mK) for the no-heat-treated sample to 0.0080 W/(mK) for the 400 °C- treated aerogels. The reason is that the reduction of macropores results in the restriction degree of gaseous thermal transfer being enhanced in aerogels, which is proved through theoretical calculation by two models. However, the thermal conductivity dramatically climbs to 0.030 W/(mK) after 800 °C owing to the pore structures being damaged and solid heat transfer gets significantly enhanced, which is confirmed by the theoretical calculation. This study suggests that appropriate high-temperature treatment to the as-prepared aerogels could improve the thermal insulation performance and the usability of silica aerogels at room temperature.

•For the first time, LTO/C composite is synthesized from metal organic framework.•LTO/C possesses regular tablet-like morphology and uniform carbon dispersion.•LTO/C exhibits superior high-rate performance and cycle stability.Carbon-coated Li4Ti5O12 composites (LTO/C) with tablet-like morphology are firstly in-situ synthesized from lithium-doped Ti-based metal-organic framework precursor by thermal annealing in N2 atmosphere at 800 and 900 °C, denoted as LTO/C-800 and LTO/C-900, respectively. The TEM and TG results demonstrate that LTO is embedded in carbon uniformly and LTO/C-800 presents more carbon content than LTO/C-900. The electrochemical results show that the LTO/C electrodes deliver a high reversible capacity, high-rate performance and excellent cycling stability as lithium-ion battery anodes. At the current density of 500 mA g−1, the reversible capacities of LTO/C-900 and LTO/C-800 are 277 and 223 mA h g−1 after 700 cycles, respectively. At 1000 and 2000 mA g−1, the reversible capacities of LTO/C-900 and LTO/C-800 can reach 181, 150 mA h g−1 and 174, 88 mA h g−1 after 1000 cycles with no attenuation, respectively. The facile and economical synthesis strategy will extend the scope of lithium-doped MOFs synthesis for other materials in energy storage application.Li4Ti5O12/C was firstly in-situ synthesized from lithium-doped Ti-based MOFs, and its cycling stability and reversible capacity were studied for LIBs.Download high-res image (144KB)Download full-size image

Novel branched carbon encapsulated MnS (MnS@C) nanochains were prepared by an in situ co-pyrolysis method. The morphology and structure of the MnS@C nanochains were mainly characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). It was found that the prepared MnS@C nanochains possess interesting branched structures, which are constructed by interconnected MnS@C nanoparticles with a diameter of ca. 200–400 nm. More interestingly, the MnS@C nanoparticles have novel “pomegranate-like” structures, in which inner cores are not made of whole nanoparticles but composed of many MnS nanoparticles. The formation mechanism of MnS@C should be attributed to an Oriented Attachment (OA) mechanism by investigating various intermediate products obtained by controlling the reaction conditions. The branched MnS@C nanochains after annealing (MnS@C-800) demonstrated perfect cycling stability and long cycle life when used as anode materials for lithium-ion batteries (LIBs). At a current density of 50 mA g−1, the stable specific capacity is around 545 mA h g−1 while the pure MnS anode experiences a drastic drop quickly to 300 mA h g−1 at the initial few cycles. At 500 mA g−1, the reversible specific capacity is ca. 318 mA h g−1 at the initial cycle and is maintained at ca. 200 mA h g−1 after 800 cycles.

Mesoporous soft carbon (MSC) was prepared from mesophase pitch using nano-CaCO3 as the template. The crystalline structure of soft carbon consists of a disordered region with a large interlayer distance benefitting sodium ion insertion/extraction and a graphitic region with good electrical conductivity favoring high rate performance. Additionally, the mesoporous structure not only shortens the path of ion diffusion but also facilitates the penetration of non-aqueous electrolytes, which can further enhance the electrochemical performance of MSC. Benefiting from its unique microstructure, the MSC delivers a reversible capacity of 331 mA h g−1 at 30 mA g−1, and retains a capacity of 103 mA h g−1 at 500 mA g−1 after 3000 cycles, indicating its excellent rate capability and cycling performance. Therefore, soft carbon with appropriate structure is expected to be another choice for anode materials of sodium ion batteries.

Porous graphene films (PGFs) were developed by introducing defects and extra edges into graphene using GO and a metal salt (ferric nitrate) as sources via a facile filtration method together with a thermal reduction and subsequent removal of the metal. The pore size and density could be controlled by simply adjusting the amount of ferric nitrate. When used as an anode for lithium ion batteries, PGF-1 showed a high reversible capacity, improved cycling stability, and ultra-high rate performance (971, 298, and 163 mA h g−1 at the rates of 10, 30, and 50 A g−1 after 10000 cycles). When used as an anode for sodium ion batteries, PGF-1 showed a reversible capacity of 195 mA h g−1 at 50 mA g−1 after 50 cycles. Even at a high rate of 1000 mA g−1, the reversible capacity can still remain at 111 mA h g−1 after 1000 cycles. The excellent performance should be attributed to the special porous structure of the PGF. On one hand, plenty of defects within the PGF provided extra reaction sites for lithium and sodium ion storage. On the other hand, the porous structure of the PGF resulted in fast diffusion and transfer of lithium/sodium ions and electrons throughout the electrodes.

With the increasing use of sodium-ion batteries (SIBs), developing cost-effective anode materials, such as metal oxide, for Na-ion storage is one of the most attractive topics. Due to the obviously larger ion radius of Na than that of Li, most metal oxide electrode materials fail to exhibit the same high performance for SIBs like that of Li-ion batteries. Herein, iron oxide was employed to demonstrate a concept that rationally designing an amorphous structure should be useful to enhance Na-ion storage performance of a metal oxide. Amorphous Fe2O3/graphene composite nanosheets (Fe2O3@GNS) were successfully synthesized by a facile approach as anodes for SIBs. It reveals that amorphous Fe2O3 nanoparticles with an average diameter of 5 nm were uniformly anchored on the surface of graphene nanosheets by the strong C–O–Fe oxygen-bridge bond. Compared to well-crystalline Fe2O3, amorphous Fe2O3@GNS exhibited superior sodium storage properties such as high electrochemical activity, high initial Coulombic efficiency of 81.2%, and good rate performance. At a current density of 100 mA/g, amorphous Fe2O3@GNS composites show a specific capacity of 440 mAh/g, which is obviously higher than the specific capacity of 284 mAh/g of crystalline Fe2O3. Even at a high current density of 2 A/g, amorphous Fe2O3@GNS composites still exhibit a specific capacity as high as 219 mAh/g. The excellent electrochemical performance should be attributed to the amorphous structures of Fe2O3 as well as strongly interfacial interaction between Fe2O3 and GNS, which not only accommodate more electrochemical active sites and provide the more transmission channels for sodium ions but also benefit electron transfer as well as effectively buffer the volume change of host materials during sodiation and desodiation. This concept for designing amorphous iron oxide anodes for SIBs is also expected to facilitate preparation of various amorphous nanostructure of other metal oxides and improve their Na-ion storage performance.Keywords: amorphous; anode; graphene; iron oxide; sodium-ion batteries

Leaky graphene oxide (LGO) was gram-scale prepared by oxidation of graphite oxide using mixed acid. The LGO showed a dual-wavelength photoluminescence (PL) with the absolute quantum yield of 11.6%. Three routes including hydrothermal method, hydrazine-assisted hydrothermal method, and hydrazine reflux were used to reduce the LGO. The contents of oxygen- and nitrogen-bearing functional groups varied depending on the reduction methods. The reduced LGOs showed a blue-shifted dual-wavelength PL and strong decrease of the quantum yields. To understand the contribution of different kind of functional groups to the PL, we used density functional theory calculation of the ground states of graphene fragments modified by various functional groups according to our experimental results. The energy gaps broadened with the removal of functional groups, indicating the blue-shift of the PL after reduction. We proposed that the blue-green PL of the LGO arose from small aromatic domains by quantum size effect. Functional groups surrounded the aromatic domains induced the red shift of the PL. The high quantum yield may ascribe to the defective and holey structure of the LGO. Our work provided a simple method to prepare high performance graphene based PL materials, and could help for understanding the nature of dual-wavelength PL.

Functional groups (FGs) in graphene oxide (GO) play an important role in the properties and applications of GO and its related materials. However, there are limited studies about the reversible transformation of FGs in response to external stimuli. In this paper, we report an experimental investigation on the response of FGs to the stimuli of transitional metal compounds. Reversible transformation of FGs on GO with loading and unloading of metal compounds was found. This interesting phenomenon could be helpful to not only enrich the reactivity of FGs in GO, but also provide new insights for designing advanced graphene-based nanomaterials.

•The synthesis ordered meosporous carbons (OMCs) with various rod lengths and different pore sizes.•The pore structural effects on the electrochemical performance of OMC as anode materials for sodium ion battery (SIB).•Propose an effective strategy for designing mesoporous materials to enhance the electrochemical performance of SIB.To investigate the pore structural effects on the electrochemical performance of ordered mesoporous carbons (OMCs) as anode materials for sodium ion battery (SIB), we prepared OMCs with various rod lengths from 350 nm to 1300 nm, and different pore sizes from 4.7 nm to 6.5 nm by changing the hydrochloric acid concentration in the P123/silica/glycerol composite system. The reversible capacities of OMCs with the average length of 350 nm, 700 nm, 900 nm and 1300 nm were 214 mA h g−1, 217.4 mA h g−1, 232.6 mA h g−1, and 228.9 mA h g−1 at 50 mA g−1, respectively. Furthermore, the OMC with largest pore size (6.5 nm) presented the highest capacity and even remained 100 mA h g−1 after 1000 cycles at 500 mA g−1 with the coulombic efficiency of nearly 100%. We confirmed that the carbon with ordered mesostructure, bigger pore size and shorter length of pore channel exhibited higher capacity. The results propose an effective direction and strategy for designing mesoporous materials to enhance the electrochemical performance of SIB.

Porous graphene nanosheets (PGNs) containing onion-like nano-holes were simply prepared using copper nitrite as template and phenolic resin as carbon source by graphitization at 2800 °C. Based on the investigations of morphology and structure, PGNs were used as anode materials for lithium-ion batteries, and it was found that this PGN electrode exhibits a stable voltage plateau, endurable Li-storage capability and outstanding rate performance of 258 mA h g−1 at 1 A g−1 and 105 mA h g−1 at 10 A g−1 after 700 cycles, superior to those of other carbon anodes with a low voltage plateau. The reasons are discussed and explained in detail.

Graphene-containing carbon aerogel (CAG) particles with morphologies of spheres, irregular semi-spheres and wrinkle-capsules were synthesized by carbonization of graphene oxide (GO)-loaded resorcinol–formaldehyde aerogels prepared by an inverse emulsion method. The effects of GO content on the morphologies and structures of CAG were explored. It was found that the morphology and particle size could be controlled and adjusted by GO concentration and the stirring rate of the resorcinol–formaldehyde inverse emulsion system, respectively. The ambient drying CAG possesses a BET specific surface area of 488 m2 g−1 with a total pore volume of 0.379 cm3 g−1 including 0.215 cm3 g−1 of micropore volume. The electrochemical properties of the prepared CAG particles were investigated as supercapacitors. When the GO concentration is 0.75 wt%, the prepared wrinkle-capsules displayed a stabilized capacity of 123.6 F g−1 under a current density of 0.1 A g−1 and 113.9 F g−1 under 1 A g−1 after 2000 cycles, and a superior specific surface area capacitance of 0.23 F m−2, indicating a good electrochemical performance and potential application in energy storage devices.

Rod-type ordered mesoporous carbons were synthesized by the direct carbonization of sulfuric-acid-treated silica/triblock copolymer composites, followed by etching the silica with a HF solution. The morphologies, microstructures and pore structures of the mesoporous carbons were investigated by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and nitrogen sorption. Their electrochemical performance as electrodes for supercapacitors was investigated by impedance spectroscopy and charge/discharge tests. It was found that the rod length of the mesoporous carbons can be changed from one to tens of micrometers by changing the synthesis parameters. The sample with the longest rod length has the highest specific capacitance. The sample with two pore sizes has the highest capacitance retention ratio of 92% at a high current density of 2 A/g.

NH2-terminated Si nanoparticles with an ultrathin silica shell have been efficiently obtained by a one-step reaction in ammonia–water–ethanol solution. Graphene nanosheet (GNS) encapsulated Si@ultrathin SiOx has been fabricated by self-assembly and thermal treatment. Because of the uniform ultrathin SiOx shell and superior GNS encapsulation structure, this material shows a reversible capacity of 2391.3 mA h g−1, maintaining 1844.9 mA h g−1 after 50 cycles at a current density of 200 mA g−1, and good rate and long cycle performance (∼700 mA h g−1 at 2000 mA g−1 after 350 cycles) as well.

We have fabricated CuO@TiO2 nanocable arrays by a facile method involving in situ thermal oxidation of Cu foil and coating of tetrabutyl titanate solution. The structure of the nanocables has been investigated by various techniques to comfirm that the cores are mainly crystalline monoclinic CuO, and the shells are crystalline tetragonal anatase TiO2. When used as an anode material for lithium-ion batteries, the nanoconfinement effect plays an important role in improving the lithium-ion storage preformance: the lithiation will be confined in one-dimensional space of TiO2 nanotubes to limit the pulverization of CuO, and the phase interface will cause an interfacial adsorption to enrich more lithium ions at some level. Benefiting from the nanoconfinement effect and interfacial adsorption, the reversible capacity does not fade, but rather increases gradually to 725 mAh g–1 after 400 cycles at a current density of 60 mA g–1, superior to the theoretical capacity of CuO.Keywords: CuO; interfacial adsorption; lithium ion battery anodes; nanocable arrays; nanoconfinement effect; TiO2;

Novel hierarchical porous carbon microspheres (HPCM) with quantities of micropores and mesopores have been prepared by an alcohol-in-oil emulsion technique using thermoplastic phenolic formaldehyde resin (PF) as the carbon source and copper nitrate (CN) as the template precursor. The effects of CN loading content on the morphology and structure of HPCM were investigated. The results showed that, when the mass ratio of PF and CN is 1:4, the HPCM not only can maintain hierarchical porous microsphere structure, but also display high electrochemical performance with a reversible capacity of 585 mA h g−1 at a current density of 50 mA g−1 and favorable high-rate performance when used as the anode materials for lithium-ion batteries.

•Activated carbon nanotubes were prepared using polyaniline as precursor.•The activated carbon nanotubes show high N, O contents and high surface areas.•Both high specific capacitance and rate capability were achieved.•Effects of surface functional groups were investigated by hydrogen reduction.A kind of nitrogen- and oxygen-containing activated carbon nanotubes (ACNTs) has been prepared by carbonization and activation of polyaniline nanotubes obtained by rapidly mixed reaction. The ACNTs show oxygen content of 15.7% and nitrogen content of 2.97% (atomic ratio). The ACNTs perform high capacitance and good rate capability (327 F g−1 at the current density of 10 A g−1) when used as the electrode materials for supercapacitors. Hydrogen reduction has been further used to investigate the effects of surface functional groups on the electrochemical performance. The changes for both structural component and electrochemical performance reveal that the quinone oxygen, pyridinic nitrogen, and pyrrolic nitrogen of carbon have the most obvious influence on the capacitive property because of their pseudocapacitive contributions.

Nitrogen-doped carbon spheres (NDCS) with average diameter of 1.05 to 2.68 μm were synthesized by a simple and eco-friendly injecting pyrolysis using pyridine as the carbon precursor. The results indicated that both the pyrolysis temperature and injecting rate play important roles in controlling the morphology of NDCS. Because of the microstructure of concentric incompletely closed graphitic shells improving the thermal stability of nitrogen functionalities, the evolution of nitrogen functionalities in NDCS was much different from other nitrogen-doped carbon materials. The formation mechanism of NDCS was discussed and deduced. When NDCS were utilized as the anode material for lithium-ion batteries, they show high-rate performance and good cyclability, suggesting the advantages of injecting pyrolysis for large-scale generating anode material in power Li-ion batteries.Keywords: Anode; Carbon spheres; Injecting pyrolysis; Li-ion battery; Nitrogen functionalities

A novel and effective route for preparing phenol formaldehyde resin grafted reduced graphene oxide (rGO-g-PF) electrode materials with highly enhanced electrochemical properties is reported. In order to prepare rGO-g-PF, hydroxymethyl-terminated PF is initially grafted to graphene oxide (GO) via esterification reaction. Subsequently, the grafted GO is reduced by the carbonization process under an inert gas atmosphere. The covalent linkage, morphology, thermal stability and electrochemical properties of rGO-g-PF are systematically investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, thermal gravimetric analysis, differential scanning calorimetry and a variety of electrochemical testing techniques. In the constructed architecture, the amorphous carbon shell can inhibit the co-intercalation of solvated lithium ion and avoid partial exfoliation of the graphene layers, thus effectively reducing the irreversible capacity and preserving the structural integrity. Meanwhile, the carbon coating layer leading to a decreased thickness of SEI film can improve the conductivity of electrode materials. As a result, the rGO-g-PF electrode exhibits impressive high cycling stability at various large current densities (376.5 mA h g−1 at 50 mA g−1 for 250 cycles, 337.8 mA h g−1 at 200 mA g−1 and 267.8 mA h g−1 at 1 A g−1 for 200 cycles), in combination with high rate capability.

Low-density graphene/carbon composite aerogels were prepared by sol–gel polymerization, ambient pressure drying and carbonization in an inert gas atmosphere. The preparation conditions, including the initial pH, solid concentration of the precursor solution, and the GO loading content, were investigated in detail. The dispersed graphene nanosheets in the carbon aerogel (CA) matrix made significant contributions to the decreased densities (as low as 0.11 g cm−3) of the CAs. The resultant composite CAs exhibited high specific surface area (>400 m2 g−1), high compression strength (19.9 MPa at a density of 0.404 g cm−3), and extremely low thermal conductivity of 0.028 W m−1 K−1, equal to one fifth of the value of the pristine carbon aerogel.

Ni-doped carbon particles with controlled morphology were synthesized by the carbonization of [Ni(H2O)6](NO3)2-doped resorcinol–formaldehyde aerogel particles extracted from an inverse emulsion polymerization system. Ni was introduced into the reaction system by directly adding nickel salt into the resorcinol–formaldehyde solution. The morphology and structure of the Ni-doped carbon particles were investigated by TEM, SEM, XRD, FI-IR and BET measurements. The size distribution of the Ni-doped carbon particles can be controlled by the stirring speed of the inverse emulsion polymerization system, and the morphology of the prepared carbon particles can be adjusted to be spheres, semispheres, irregular semispheres and capsules by changing the nickel salt concentration. The Ni particles were distributed uniformly in the carbon network. This study illustrates that [Ni(H2O)6](NO3)2 changed the resorcinol–formaldehyde inverse emulsion polymerization mechanism. Upon ambient drying, the Ni-doped carbon particles exhibit mainly microporosity and the BET surface area of the samples can reach 487 m2 g−1 with a corresponding pore volume of 0.229 cm3 g−1. The electrochemical performance was tested using these carbon particles as the electrode material for supercapacitors. The prepared carbon capsules displayed a stabilized capacity of 154 F g−1 after 1200 cycles with an increasing trend, which indicates that the materials have good electrochemical performance.

Cobalt hydroxide arrays/graphene nanosheets (Co(OH)2 array/GNSs) composites are formed by the growth of preferential-orientation versus basal planes of GNSs. Notably, the Co(OH)2 nanoplates, possessing special hexagonal morphology with the length of about 130 nm and average thickness of about 20 nm, stand vertically rather than lie flat on the surface of graphene sheets. More interestingly, the (001) crystal plane of Co(OH)2 is vertical to the graphene basal plane and forms strong covalent bond interaction (Co–C bond) with the graphene layer, which could be a driving force for the preferential growth of nanoarrays on graphene. Co(OH)2 array/GNSs composites exhibit not only high specific capacity, but also outstanding high-rate performance when used as anode materials for lithium-ion batteries. At the current density of 50 mA g−1, the reversible capacity is 976 mA h g−1 and remains at 1103 mA h g−1 after 50 cycles without any fading. At 500 and 1000 mA g−1, the reversible capacities can reach 696 and 496 mA h g−1, which are 71% and 51% of that at 50 mA g−1, respectively. Excellent electrochemical performance could be attributed to the array structure of Co(OH)2 as well as a synergistic effect between Co(OH)2 and graphene. Therefore, Co(OH)2 array/GNSs composites are expected to have potential applications in LIBs.

Generally speaking, excellent electrochemical performance of metal oxide/graphene nanosheets (GNSs) composite is attributed to the interfacial interaction (or “synergistic effect”) between constituents. However, there are no any direct observations on how the electronic structure is changed and how the properties of Li-ion storage are affected by adjusting the interfacial interaction, despite of limited investigations on the possible nature of binding between GNSs and metal oxide. In this paper, CuO nanosheets/GNSs composites with a little Cu2O (ca. 4 wt %) were utilized as an interesting model to illustrate directly the changes of interfacial nature as well as its deep influence on the electronic structure and Li-ion storage performance of composite. The interfacial adjustment was successfully fulfilled by removal of Cu2O in the composite by NH3·H2O. Formation of Cu–O–C bonds on interfaces both between CuO and GNSs, and Cu2O and GNSs in the original CuO/GNSs composites was detected. The small interfacial alteration by removal of the little Cu2O results in the obvious changes in electronic structure, such as weakening of covalent Cu–O–C interfacial interaction and recovery of π bonds in graphene, and simultaneously leads to variations in electrochemical performance of composites, including a 21% increase of reversible capacity, degradation of cyclic stability and rate-performance, and obvious increase of charge-transfer resistance, which can be called a “butterfly effect” in graphene-based metal oxide composites. These interesting phenomena could be helpful to design not only the high-performance graphene/metal oxide anode materials but also various advanced graphene-based composites used in the other fields such as sensors, catalysis, fuel cells, solar cells, etc.Keywords: Cu2O; CuO; graphene; interfacial interaction; lithium-ion battery; NEXAFS

Application of iron fluoride, a promising candidate of cathode materials for lithium ion batteries, is being hindered by its poor electrochemical performance caused by low electronic conductivity and large volume change. Design of carbon-encapsulated transitional metal compounds (including fluoride, oxide, sulfide, etc.) structure is one of the most effective strategies in improving their lithium-ion storage performance. In this work, we successfully synthesize for the first time carbon-nanotube-encapsulated FeF2 nanorods via a facile in situ co-pyrolysis of ferrocene and NH4F. This kind of core/shell carbon nanotube/FeF2 nanorod exhibits better cyclic stability and rate-performance used as cathode materials. Better electrochemical performance of the nanorods should be attributed to the protection of the carbon shell because, experimentally, it is observed that outer carbon shells suffer from high internal stress during Li-ion insertion but efficiently keep the nanorods in the one-dimensional morphology and make nanorods a good electrical contact with the conductive carbon black. This work not only prepares high-performance core/shell carbon/iron fluoride cathode materials, but should also open a facile pathway for design of various novel nanostructures of other metal fluoride/carbon core/shell structures for future lithium-ion batteries.Keywords: carbon nanotube; cathode; co-pyrolysis; encapsulation; iron fluoride; lithium-ion batteries

Graphene nanosheets can be driven to change their conformation by melting metal and, finally, a cocoon coating can be constructed to encapsulate the metal sphere. Interaction beween metal and oxygenated defects plays a leading role in conformational changes of graphene nanosheets.

•Graphene/polyaniline composite was self-assembled to a spherical tremella-like structure.•The composite shows high specific capacitance and good rate performance along with long cycle life for supercapacitors.•The high performance is attributed to the 3D interconnected structure, the synergic effect of both the components and the mechanical stability of the composite.A novel tremella-like graphene/polyaniline composite was achieved from self-assembly of graphene nanosheets during polymerization of aniline in H2O/N, N-dimethylformamide solution, and was further employed as an electrode for supercapacitors. This graphene/polyaniline composite demonstrates a spherical tremella-like structure and a large specific capacity of 497 F g−1 at a current density of 0.5 A g−1. Particularly, an outstanding rate capability of 456 F g−1 under 5 A g−1 after 1000 cycles was obtained. Scanning electron microscopy showed that polyaniline nanoparticles were uniformly deposited on free-standing graphene nanosheets, and self-assembled to a spherical tremella-like structure. Therefore, this unique nanostructure is promising for high-performance electrochemical applications.

In order to strengthen the nanostructure and suppress the collapse of nanopores of resorcinol–formaldehyde (RF) aerogels during the drying process, graphene oxide (GO) was incorporated into the RF matrix to prepare GO–RF composite aerogels by sol–gel polymerization. The influences of GO content on the sol–gel process, structure, and physical properties of RF aerogels were investigated. The morphologies of composite aerogels were characterized by scanning electron microscopy and transmission electron microscopy, and it was found that GO was well dispersed in the RF matrix. In addition, GO can obviously accelerate the gelation of the RF solution and reduce both the drying shrinkage and aerogel density. As the content of GO increased from 0 to 2 wt%, both the linear shrinkage and density of composite aerogels decreased progressively from 28.3% to 2.0% and 506 to 195 kg m−3, respectively, implying that GO is an effective additive for inhibiting the volume shrinkage of aerogels during the drying process.

Highly wrinkled reduced graphene oxide nanosheets were prepared by chemical exfoliation from ball-milled graphite powder. This wrinkled graphene nanosheets showed higher sensitivity and simpler recovery ability than the flat reduced graphene oxide nanosheets when used as the NH3 gas detector. According to both experimental analysis and theoretical calculation, the favourable sensing properties were attributed to a specific curved structure which allowed a stronger energy change in the response process and a free diffusion space for sensor recovery.

Si@SiO2 core–shell, yolk–shell, and SiO2 hollow structures can be obtained when Si nanoparticles are simply treated with ammonia–water–ethanol solution at room temperature. Their formation mechanism is attributed to the self-templated etching–deposition process.

In most of the reports, ball-milling of graphitic materials would lead to the decrease of their crystal degree and further amorphization. However, large crystal enhancement of carbon black and graphitized carbon black induced by ball milling were herein observed. The hollow structure of the graphitized carbon black remained without collapse. But from high resolution transmission electron microscopy, the morphology of each nanoparticle is changed from polyhedron to sphere after a certain time of ball-milling. Accordingly, a transformation model was proposed.

We reported a universal approach to prepare carbon nanotubes from solid-state carbons. Under the assistance of a trace amount of water vapor, efficient growth of types of carbon nanotubes were achieved from commercially available artificial graphite powder, carbon black, and amorphous carbon powder under a relatively low temperature of 850 °C. This present method provided a new horizon for the effective utilization of low value added carbon resources to fabricate advanced carbon materials and could help to deeply understand the structure transformation of solid carbon materials.

Due to its inert closed-shell structure, the graphitic onion-like carbon (GOC) could not be exfoliated into a graphene-like structure by a simple Hummers' method even under rigorous conditions. Herein, we successfully exfoliated GOC into twisted graphene oxide nanosheets by the cooperation of chemical activation and Hummers' oxidation. Porphyra-like graphene nanosheets were further prepared from the twisted graphene oxide nanosheets by rapid thermal expansion. The defects introduced by activation were considered to play significant roles in the unfolding of GOC because they provide reactive sites for the oxidation. As an anode material for lithium ion batteries, the obtained porphyra-like graphene exhibited much better electrochemical properties than those of GOC. Our work can contribute to (1) deeply understand the exfoliation mechanism of graphitic materials by chemical oxidation especially the influence of defects during these steps; and (2) provide new strategies for designing functional graphene based materials from inert graphitic structures.

By using KMnO4 as both the oxidant and Mn source in a modified Hummers’ method, a facile and economical procedure is proposed to synthesize graphene oxide/MnO2 composite. Then after annealing at 400 °C, the graphene/Mn3O4 composite with 70.7 wt.% Mn3O4 nanoparticles homogeneously anchored on each side of graphene nanosheets is obtained. The electrochemical performance of the graphene/Mn3O4 is investigated as a supercapacitor electrode material. It exhibits the high specific capacitance of 271.5 F g−1 at the current density of 0.1 A g−1 as well as great cycle performance. At the high current density of 10 A g−1, the capacitance retention even keeps about 100% after 20,000 cycles. The good electrochemical performance and the simple accessibility make this graphene/Mn3O4 composite a promising candidate as a supercapacitor electrode material.Highlights► Graphene oxide/manganese oxide composite is synthesized via a one-step strategy. ► KMnO4 is utilized as both the oxidant and Mn sources for the composite. ► Graphene/Mn3O4 exhibits high capacitance of 271.5 F g−1and great cycle stability.

•The poly-condensation of anthracene mixed with Lewis acids.•Transformation of Lewis acid during the carbonization and graphitization.•ZrO2 and ZrC doped mesophase pitches.•The removal of catalysts from pitches.In this work, we examine the poly-condensation of anthracene mixed with aluminum trichoride (AlCl3) or zirconium tetrachloride (ZrCl4) at 350 °C and 1.5 MPa, investigating the catalyst transformations during poly-condensation and through further heat treatment to 1000 °C (carbonization) and 2800 °C (graphitization). The mesophase transformation reveals that AlCl3 exhibits a higher catalytic activity than ZrCl4, while the ash content indicates that the resulting pitches perfectly retain both AlCl3 and ZrCl4 after poly-condensation and carbonization. X-ray diffraction (XRD) pattern and X-ray photoelectron spectroscopy (XPS) show the details of the catalyst transformation. The AlCl3 deliquesces into hydroxides during poly-condensation, and a part of Al(OH)3 decomposes into Al2O3 at 1000 °C, while the ZrCl4 converts into ZrO2 during poly-condensation and carbonization. The graphitization volatilizes the Al component and results in no aluminum detected. A part of ZrO2 retained in the pitch transforms into ZrC after graphitization. The results of this investigation are beneficial for optimizing the removal of Lewis catalysts, and the prepared mesophase pitch, which containing ZrC and ZrO2, could be used as a functional material precursor.

CuO nanowires were synthesized by in situ thermal oxidation of Cu2O for the first time in the temperature range of 300–750 °C in air. In this process, the effects of annealing temperature and growth time on the growth of CuO nanowires were investigated by SEM, XRD, EDS mapping and line-scan profile measurements. We found that the nucleation of CuO nanowires is a solid-state transformation process, and the nanowire length obeys a parabolic law with annealing time. The nanowire growth shows a diffusion-controlled behavior. Based on the above-mentioned study, the mechanism of the nucleation and growth of CuO nanowires from Cu2O is proposed.

The coalescence and structural transformation of closed-shell graphitic carbon (CGC) induced by KOH activation were investigated by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and Raman spectroscopy. It was found that with graphitization at 2800 °C, CGC retains a nanosized polyhedral structure with a diameter of ca. 25 nm. These thermally stable CGC nanoparticles could be coalesced and reconstructed to form a micron-sized dish stacked structure when treated by low temperature KOH activation at 400 °C. Each of the obtained carbon dishes retained a high crystallinity and possessed few layer graphene-like structure with closed loop edges. During activation, defects, disordered carbon atoms and dangling bonds were introduced into the CGC, which provide active positions for the coalescence and reconstruction of these nanoparticles. With the destruction of the closed-shell structure and the structural transformation, the inner-stress of these polyhedral nanoparticles was released. Accordingly, a possible formation mechanism was suggested.

A method to detect the intrinsic capacitance and thickness of graphene nanosheets (GNS) was developed. The ultrasonic-dispersed GNSs were separated by a kind of small-powder graphite (SG, 0.5–2 μm) with almost no capacitance to prevent the ultra-thin graphene layer from restacking face to face. In order to separate the GNSs as much as possible, we increased the mass ratio of SG in the GNS–SG composite gradually from 1:10 to 1:250. The electrochemical properties of different GNS–SG composites as electrode materials for an electric double-layer capacitor (EDLC) have been systematically investigated. It was found that, as the content of GNSs decreased from pure GNS to 1/100 of the GNS–SG composite, specific capacitance increased progressively from 171.8 F g−1 to 417.1 F g−1. As the ratio of GNSs in the GNS–SG electrodes was decreased further (1:200, 1:250 and 1:300), the specific capacitance held a stable value of ∼856.6 F g−1, revealing the intrinsic capacitance of these GNSs. Based on the theoretical specific surface area of graphene and capacitance of a common graphite electrode, the layer number of GNSs here was calculated to be 2–11. This strategy can not only calculate the average layer number but also preliminarily judge the aggregation of GNSs from the capacitance data.

Novel hierarchical porous carbon nanosheets (HPCS) with quantities of micropores and mesopores were prepared on a large-scale by using thermoplastic phenolic formaldehyde resin as the carbon source and copper nitrate as the template precursor. The HPCS, possessing a thickness of about 40 nm and the width of several microns, exhibited a high specific capacity and favorable high-rate performance when used as an anode material for lithium ion batteries (LIBs). The reversible capacities were 748 mA h g−1 at a current density of 20 mA g−1 and 460 mA h g−1 even at 1 A g−1, which were much higher than those of traditional porous carbon materials. It also showed superior cyclical stability for only 0.3% capacity loss per cycle under high rate charge-discharge process, suggesting that HPCS should be a promising candidate for anode materials in high-rate LIBs. The roles of various-sized pores in HPCS in Li storage were discussed briefly.

Solution-based oxidation has been widely utilized to prepare graphene oxide or graphene nanoribbons from different carbon precursors, but some details of the exfoliation or unzipping processes still remain elusive. Here, we put forward three graphitic systems for deep understanding of the top-down route. Based on the oxidation-intercalation synergistic effect, the formation mechanisms were proposed.

Carbon nanotube-encapsulated SnO2 (SnO2@CNT) core–shell composite anode materials are prepared by chemical activation of carbon nanotubes (CNTs) and wet chemical filling. The results of X-ray diffraction and transmission electron microscopy measurements indicate that SnO2 is filled into the interior hollow core of CNTs and exists as small nanoparticles with diameter of about 6 nm. The SnO2@CNT composites exhibit enhanced electrochemical performance at various current densities when used as the anode material for lithium-ion batteries. At 0.2 mA cm−2 (0.1C), the sample containing wt. 65% of SnO2 displays a reversible specific capacity of 829.5 mAh g−1 and maintains 627.8 mAh g−1 after 50 cycles. When the current density is 1.0, 2.0, and 4.0 mA cm−2 (about 0.5, 1.0, and 2.0C), the composite electrode still exhibits capacity retention of 563, 507 and 380 mAh g−1, respectively. The capacity retention of our SnO2@CNT composites is much higher than previously reported values for a SnO2/CNT composite with the same filling yield. The excellent lithium storage and rate capacity performance of SnO2@CNT core–shell composites make it a promising anode material for lithium-ion batteries.Highlights► Carbon nanotube-encapsulated SnO2 core–shell composites are prepared by simple method. ► The etching defects on carbon nanotubes are helpful to increase SnO2 filling yield. ► Selective cleaning ensures SnO2 only filled into the interior hollow cores of CNTs. ► The composites exhibit good electrochemical performance at high current densities.

TixSn1−xO3 solid solutions were prepared by a hydrothermal process. The morphologies and structures of TixSn1−xO3 solid solutions were investigated by scanning electron microscope, transmission electron microscope and X-ray diffraction measurements. The electrochemical properties of TixSn1−xO3 solid solution electrodes with different Sn/Ti ratios were examined by a variety of electrochemical testing methods. It was found that, the TixSn1−xO3 solid solution showed not only higher specific capacity of 506 mAh g−1 after 30 cycles but also better cycle performance, superior than the pure SnO2 electrode, which can be ascribed to the stable cyclability of TiO2 and the high reversible capacity of nanosized SnO2. The TixSn1−xO3 solid solutions would be a potential candidate as anode material for a new generation lithium ion batteries.

Iron titanium oxide (Fe1.5Ti0.5O3) nanoparticles with the diameter of about 150 nm were prepared by hydrothermal process and further heat treatment at 300 °C for 2 h. The morphology, structure and electrochemical performance of Fe1.5Ti0.5O3 nanoparticles as anode material for lithium-ion batteries were investigated by scanning electron microscopy, X-ray diffraction and a variety of electrochemical testing techniques. It was found that, compared with TiO2 and Fe2O3, the iron titanium oxide electrode exhibited higher specific capacity of 734.9 mAh g−1 after 50 cycles at the current density of 50 mA g−1, good cycle stability and high-rate performance, suggesting that the Fe1.5Ti0.5O3 nanoparticle synthesized by this method is a promising anode material for lithium-ion batteries.

Carbon/carbon (C/C) composites were prepared using multiple cycle in situ mesophase densification in the presence of zirconium chloride. The mesophase transformation and the performance of C/C composites were investigated in detail. The results show that higher amount of ZrCl4 and longer soaking time accelerate the condensation of aromatic hydrocarbons. Additionally, the XRD pattern and ash contents show that the ZrCl4 is retained in the samples and transformed to t-ZrO2 and m-ZrO2 after carbonization. In all the composites, the bulk density increases with cycle times, and the flexural strength increases with bulk density. However, a decrease of flexural strength for low density composites was observed when increasing ZrCl4 concentrations. This tendency is attributed to more ZrO2 formation in the composites using 20 wt.% ZrCl4. Subsequently, these ZrO2 particles produce interface defects in the matrix which decreases its strength. Attributed to the very low content of ZrO2 in high density composites, there is no difference between the samples using 13 wt.% and 20 wt.% ZrCl4.

The confinement of Sn nanoparticles inside few-walled carbon nanotubes and its effect on lithium ion storage property have been investigated in detail. It was found that the charge transfer and electronic interaction facilitated Sn to remain in a more reduced state and to link strongly with interior surface of carbon nanotubes by Sn–C bonds, leading to a high reversible capacity of 732 mAh g–1 and capacity retention of 639.7 mAh g–1 after 170 cycles at 50 mA g–1. We also found that the volume restriction inside CNTs protected Sn–C bonds against breakage during lithium insertion/extraction, contributing to the excellent cycling performance with the fade rate of only 0.074% per cycle.

A novel flat cake-type ordered mesoporous carbon was directly prepared by a one-step hard templating method simultaneously using the nonionic surfactant Pluronic P123 (EO20PO70EO20) and cationic surfactant cetyltrimethylammonium bromide (CTAB) as both the structure-directing agent and carbon precursor.

Ordered mesoporous carbons with various morphologies, including rod-like, gyroid-shaped, plate-like and flower-type, were synthesized by changing the hydrochloric acid concentration in the formation of silica/triblock copolymer P123/glycerol composites and further carbonization. Triblock copolymer P123 and glycerol were used as both the structure-directing agents and the carbon precursors. The morphologies, structures and pore characteristics of the carbon materials were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen sorption techniques. The electrochemical performances of the carbons as electrodes for supercapacitors were measured. The relationships between the capacitive behavior, the morphology and the pore characteristics were elucidated briefly. It was found that the sample possessing the highest surface area of 1312 m2 g−1 exhibits the highest specific capacity of 164 F g−1 among the five samples at a current density of 100 mA g−1, and decreases from 164 to 142 F g−1 with an increase in current density from 100 to 2000 mA g−1. The capacitance retention ratio (relative to the capacitance at a current density of 100 mA g−1) of the sample with short rods at a current density of 2000 mA g−1 (94.4%) is much higher than that of the sample with long rods (86.6%), which could be partly ascribed to its shorter pore channels.

Iron sulfide-embedded carbon microspheres were prepared via a solvothermal process and show high specific capacity and excellent high-rate performance as anode material for lithium-ion batteries.

Carbon-encapsulated iron nanostructures were prepared by co-carbonization of a mixture of aromatic heavy oil and ferrocene. The morphologies and structural features of the iron/carbon composites were investigated using transmission electron microscopy, high-resolusion transmission electron microscopy and X-ray diffraction measurements. It was found that, by increasing the reaction temperature from 420 to 450 °C the product was changed from nanoparticle to nanorod. The morphologies of the products prepared at 440 °C proved the relationship between nanoparticle and nanorod. Therefore, a model was established to explain the formation mechanism of carbon-encapsulated iron nanorods from the aggregation and self-assembly of partially fused carbon-encapsulated iron nanoparticles.Graphical abstractResearch highlights► Carbon-encapsulated iron nanostructures were prepared by a co-carbonization process. ► Carbon-encapsulated iron nanorod evolves from carbon-encapsulated iron nanoparticle. ► Cooling process is essential to the formation of carbon-encapsulated iron nanorod.

Multi-walled nitrogen-doped carbon (CNx) nanotubes, synthesized by an aerosol-assistant catalytic chemical vapor deposition technique, were investigated for electrochemical intercalation with lithium. Nanotube morphologies and nitrogen contents in the samples produced from toluene and acetonitrile taken in various proportions were determined by transmission electron microscopy and X-ray photoelectron spectroscopy. It was found that the first discharge capacity of CNx electrodes increases with nitrogen content. The irreversible capacity was partially attributed to pyridinic-like nitrogen atoms, which can strongly bind with Li ions confirmed by result of quantum-chemical calculation. The CNx electrode with the lowest nitrogen content (∼1 at.%) in the considered set of the samples showed the highest reversible capacity 270 mAh g−1 at the current density of 0.2 mA cm−2 and the highest value of exchange current density, suggesting that the electrochemical activity of carbon nanotubes is enhanced by light incorporation of nitrogen atoms.

The structure and electronic properties of graphene nanosheet (GNS) render it a promising conducting agent in a lithium-ion battery. A graphite electrode loaded with GNS exhibits superior electrochemical properties including higher rate performance, increased specific capacity and better cycle performance compared with that obtained by adding the traditional conducting agent–acetylene black. The high-quality sp2 carbon lattice, quasi-two-dimensional crystal structure and high aspect ratio of GNS provide the basis for a continuous conducting network to counter the decrease in electrode conductivity with increasing number of cycles, and guarantee efficient and fast electronic transport throughout the anode. Effects of GNS loading content on the electrochemical properties of graphite electrode are investigated and results indicate that the amount of conductive additives needed is decreased by using GNS. The kinetics and mechanism of lithium-storage for a GNS-loaded electrode are explored using a series of electrochemical testing techniques.

Copper oxide hollow nanoparticles/graphene-nanosheet composites are prepared using the Kirkendall-effect approach. The composites exhibit a durable lifetime cycle at high rates. The reversible capacity of the material attains 640 mAhg− 1 at 50 mAg− 1 and the capacity retention is ca. 96% when the current density is increased 10 times. At 1 Ag− 1 (ca. 1.7 C), the reversible capacity reaches 485 mAhg− 1 and remains at 281 mAhg− 1 after 500 cycles, indicating that the capacity fading is less than 0.4 mAhg− 1 per cycle. This excellent electrochemical performance can be attributed to the hollow interior of CuO nanoparticles as well as synergistic effect between CuO and graphene.Highlights► The CuO hollow nanoparticles/graphene composite (CuO-HNPs/G) was prepared via the Kirkendall effect. ► CuO-HNPs/G exhibits the excellent rate capabilities. ► CuO-HNPs/G holds durable cycle life (500 cycles) at high rate.

Graphene nanosheets (GNSs) loading graphene-encapsulated iron microspheres (GEIMs) were fabricated by heat treatment of graphene oxide nanosheets (GONs) with ferric trichloride (FeCl3). The special pentagon-hexagonal graphene shells have been produced by precipitation of carbon from metal carbide solutions, thanks to the high reactivity of GONs and ferric nanoparticles dispersing homogeneously between graphene layers. The morphology, structure and elemental composition of GEIMs were investigated by scanning electron microscope, X-ray diffraction and electron energy disperse spectroscope, respectively. The formation mechanism of GEIMs was proposed. Hollow graphene microspheres (HGMs) on the GNSs were obtained with the removal of ferric species in GEIMs. When used as the anode materials for lithium-ion batteries, the almost graphitic HGMs exhibit stable voltage platform at ca. 0.2 V, excellent cycle capability and higher reversible capacity of about 440 mAh g−1 after 50 cycles and possess great potential application in lithium–ion batteries.

We explore in-depth the interfacial interaction between Fe3O4 nanoparticles and graphene nanosheets as well as its impact on the electrochemical performance of Fe3O4/graphene anode materials for lithium-ion batteries. Fe3O4/graphene hybrid materials are prepared by direct pyrolysis of Fe(NO3)3·9H2O on graphene sheets. The interfacial interaction between Fe3O4 and graphene nanosheets is investigated in detail by thermogravimetric and differential scanning calorimetry analysis, Raman spectrum, X-ray photoelectron energy spectrum and Fourier transform infrared spectroscopy. It was found that Fe3O4 nanoparticles disperse homogeneously on graphene sheets, and form strong covalent bond interactions (Fe–O–C bond) with graphene basal plane. The strong covalent links ensure the high specific capacity and long-period cyclic stability of Fe3O4/graphene hybrid electrodes for lithium-ion batteries at high current density. The capacity keeps as high as 796 mAhg−1 after 200 cycles without any fading in comparison with the first reversible capacity at the current density of 500 mAg−1 (ca. 0.6 C). At 1 Ag−1 (ca. 1.3 C), the reversible capacity attains ca. 550 mAhg−1 and 97% of initial capacity is maintained after 300 cycles. This work reveals an important factor affecting the high-rate and cyclic stability of metal oxide anode, and provides an effective way to the design of new anode materials for lithium-ion batteries.

Microspheres composed of multilayer graphene (MMG) had been prepared by the chemical reduction of graphene oxide at 100 °C. The morphology, structure and electrochemical performance of MMG as anode material for lithium-ion batteries were investigated by high-resolution transmission electron microscope, scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical testing techniques. It is found that the specific capacity of MMG (453 mAh g−1) is almost twice that of multilayer graphene (MG, 229 mAh g−1). Furthermore, MMG exhibits good cycle performance and high-rate charge/discharge properties.Research highlights► In this study we had prepared the microspheres composed of multilayer graphene (MMG). ► The specific capacity of MMG is almost twice that of multilayer graphene. ► MMG exhibits good cycle performance and high-rate charge/discharge properties.

Polyaniline (PANI)/ordered mesoporous carbon (OMC) composites were prepared by in situ polymerization of aniline. The effects of PANI loading on the electrochemical properties were tested by galvanostatic charge/discharge, cyclic voltammetry, and AC impedance. It was found that the composites showed higher specific capacitances than pure OMC or PANI. They also had good charge-discharge cycling stability. The capacitance of the composite containing 60% PANI could reach 409 F·g−1 at a current density of 0.1 A·g−1.

Silicon carbide (SiC) nanowires were fabricated in a large quantity by a rapid heating carbothermal reduction of a novel resorcinol-formaldehyde (RF)/SiO2 hybrid aerogel in this study. SiC nanowires were grown at 1500 °C for 2 h in an argon atmosphere without any catalyst via vapor–solid (V–S) process. The β-SiC nanowires were characterized by field-emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM) equipped with energy dispersive X-ray (EDX) facility, Fourier transformed infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The analysis results show that the aspect ratio of the SiC nanowires via the rapid heating process is much larger than that of the sample produced via gradual heating process. The SiC nanowires are single crystalline β-SiC phase with diameters of about 20–80 nm and lengths of about several tens of micrometers, growing along the [1 1 1] direction with a fringe spacing of 0.25 nm. The role of the interpenetrating network of RF/SiO2 hybrid aerogel in the carbothermal reduction was discussed and the possible growth mechanism of the nanowires is analyzed.

Graphene oxide was prepared by ultrasonication of completely oxidized graphite and used to improve the flame retardancy of epoxy. The epoxy/graphene oxide nanocomposite was studied in terms of exfoliation/dispersion, thermal stability and flame retardancy. X-ray diffraction and transmission electron microscopy confirmed the exfoliation of the graphene oxide nanosheets in epoxy matrix. Cone calorimeter measurements showed that the time to ignition of the epoxy/graphene oxide nanocomposite was longer than that of neat epoxy. The heat release rate curve of the nanocomposite was broadened compared to that of neat epoxy and the peak heat release rate decreased as well.

Air oxidation can result in the motion of metal confined in carbon nanotubes (CNTs). This can also be utilized to tailor various hybrid nanostructures. By controllable air-oxidation, as-prepared metal@CNT nanorods (a) can be converted first to core−shell−void nanorods (b), then to metal/metal oxide@CNT nanotubes (c), and finally to mesoporous metal oxide nanotubes (d). The metal/metal oxide@CNT nanotubes and mesoporous metal oxide nanotubes are expected to find many applications, such as in lithium ion batteries, catalysis, magnetic drug delivery, and gas sensing.

Hollow graphene oxide spheres (HGOSs) were fabricated from graphene oxide nanosheets (GONs) utilizing a water-in-oil (W/O) emulsion technique without surfactant. Effects of oxidation treatment and water removal on the formation and morphology of HGOSs are investigated. The oxidation time for preparing GONs is a crucial factor for the formation and morphology of HGOSs. We found that with increasing oxidation time, the morphology and surface topography of HGOSs vary from irregular and rough to uniform and smooth shape with decreasing diameter. Moreover, the electrochemical performance of HGOSs as anode materials in lithium-ion batteries was evaluated. The heat-treated HGOSs exhibit a 485 mAh g−1 reversible capacity and high rate performance thanks to the hollow structure, thin and porous shells consisting of graphene.

Novel carbon nanotubes (CNTs) were prepared on a large-scale. Their morphology and structure were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman measurements. It was found that the prepared CNTs possess a quadrangular cross section, as well as one open end and “herringbone”-like walls, so these novel CNTs were named q-CNTs. The unique morphology of q-CNTs implies broad potential applications in many fields, including drug delivery, conductive and high-strength composites, field emission displays and radiation sources, hydrogen storage media, and supercapacitors. When used as the anode materials for lithium-ion batteries, q-CNTs exhibit excellent high-rate performance (a high-reversible capacity of 181 mAh g−1 at the current density of 1000 mA g−1 (ca. 3 C)), which is much higher than that of the common multi-wall carbon nanotubes. This high-rate performance should be attributed to the unique nanostructure of q-CNTs, which results in a high diffusion coefficient for lithium ions in the q-CNTs.

Graphite oxide was prepared by the Hummers method. Then after further oxidation, a new kind of carbon nanoparticle, with diameter 10–30 nm, was formed in the aqueous solution. On the basis of structural characterization by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy it is deduced that the nanoparticles are generated by the self-assembly of few-layer graphene oxides. A possible formation mechanism is proposed.

Graphene nanosheets (GNSs) with narrow mesopore distribution around 4 nm were mass-produced from natural graphite via the oxidation and rapid heating processes. The effects of oxidant addition on the morphology, structure and electrochemical performance of GNSs as electrode materials for electric double-layer capacitor (EDLC) were systematically investigated. The electrochemical properties of EDLC were influenced by the specific surface area, pore characteristics, layer stacking and oxygen-containing functional group contents of electrode materials. Deeper oxidation makes graphite possess both higher specific surface area and more graphene edges, which are favorable for the enhancement of capacitive performance of EDLC. The electrodes with freestanding graphene nanosheets prepared by coating method exhibited good rate capability and reversibility at high scan rates (to 250 mV s−1) in electrochemical performances. GNS electrode with specific surface area of 524 m2 g−1 maintained a stable specific capacitance of 150 F g−1 under specific current of 0.1 A g−1 for 500 cycles of charge/discharge.

Nitrogen-containing carbon nanotubes (CNTs) with open end and low specific surface area were prepared via the carbonization of polyaniline (PANI) nanotubes synthesized by a rapidly mixed reaction. On the basis of analyzing the morphologies and structures of the original and carbonized PANI nanotubes, the electrochemical properties of PANI-based CNTs obtained at different temperatures as electrode materials for supercapacitors using 30 wt.% aqueous solution of KOH as electrolyte were investigated by galvanostatic charge/discharge and cyclic voltammetry. It was found that the carbonized PANI nanotubes at 700 °C exhibit high specific capacitance of 163 F g−1 at a current density of 0.1 A g−1 and excellent rate capability in KOH solution. Using X-ray photoelectron spectroscopy measurement the nitrogen state and content in PANI–CNTs were analysed, which could play important roles for the enhancement of electrochemical performance. When the appropriate content of nitrogen is present, the presence of pyrrole or pyridone and quaternary nitrogen is beneficial for the improvement of electron mobility and the wettability of electrode.

Carbon-encapsulated iron and nickel magnetic nanoparticles (CEMNPs) were synthesized from their salt precursors using an instant pyrolysis method. The morphologies, structural features and magnetic properties of the particles were investigated by transmission electron microscopy, X-ray diffraction, simultaneous thermogravimetry-differential scanning calorimetry and vibrating sample magnetometry. It was found that almost all of the CEMNPs were spherical, and their size changed from 10 to 30 nm, whereas the size of the carbon-encapsulated iron nanoparticles changed from 50 to 60 nm. The magnetic properties of the products indicated that the carbon-encapsulated iron nanoparticles were paramagnetic and their properties were tunable with the iron content. The present approach is promising for large-scale production of CEMNPs.

A novel and general strategy for the synthesis of carbon-encapsulated metal oxide hollow nanoparticles (HNPs) and pure metal oxide HNPs was developed from carbon-encapsulated metal nanoparticles by controlled oxidation in the air. The materials were characterized by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction measurements. It was found that the morphologies and compositions of HNPs were easily tailored through adjustment of the oxidation conditions. When used as the anode materials for lithium-ion batteries, carbon-encapsulated α-Fe2O3 HNPs exhibit excellent cycling performance and a higher reversible capacity of about 700 mA h g−1 after the 60th cycle and possess great potential application in lithium-ion batteries.

We synthesized α-Fe2O3 hollow nanoparticles by directly oxidizing the carbon-encapsulated iron carbide (Fe3C@C) nanoparticles in air. In this paper, the conversion mechanism of Fe3C@C to hollow nanoparticles was deduced in detail by comparatively investigating the morphologies and compositions of the oxidized products at different oxidation stages using transmission electron microscope (TEM), high resolution TEM (HRTEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It was found that both oxygen and carbon play important roles in the formation of hollow nanostructures, wherein oxygen is the driving force for the outward diffusion of core species and the carbon shell not only provides the diffusion vacancies but also effectively moderates the interdiffusion rates of metal core materials and oxygen. A growth model was proposed: during the oxidation process, three diffusion processes occur including the inward diffusion of oxygen along the carbon shell, outward diffusion of core materials, and inward diffusion of vacancies from carbon shell to core. The outward diffusion of core species involves two steps: the first step is the diffusion of Fe3C from core to carbon shells, which is only a physical change (single-crystal Fe3C was changed to multicrystal Fe3C); and the second one is the diffusion and chemical reactions of Fe3C in carbon shells with oxygen (the multicrystal Fe3C was oxidized to Fe3O4 and then to α-Fe2O3). The two-step diffusion is a theoretical extension to the nanoscale Kirkendall effect, which is expected to be valid in other diffusion couples and theoretical simulation.

A novel spherical ordered mesoporous carbon with a high surface area and cage-type porous structure was prepared by direct carbonization of silica/triblock copolymer/butanol composite using F127 and butanol as both structure-directing agent and carbon precursor.

An easy method is described for the synthesis of a mesostructured Ni/ordered mesoporous carbon (OMC) composite with a highly ordered cubic structure (space group Im3m). This synthesis was carried out by the carbonization of the F127/[Ni(H2O)6](NO3)2/RF (resorcinol-formaldehyde) composite self-assembled in an alkaline medium. The effects of nickel loading content and carbonization temperature on the morphologies, pore features, structures and magnetic properties of these Ni/OMC composites were investigated using the thermogravimetric analysis, X-ray diffraction, nitrogen sorption, transmission electron microscopy and vibrating-sample magnetometer measurements. It was found that Ni2+ was captured by the network of F127/RF and further reduced into metallic Ni nanoparticles during the carbonization. The nickel nanoparticles were well-dispersed in the ordered mesoporous carbon walls. The Ni/OMC composites exhibit the soft ferromagnetic behavior and the magnetization parameters can be adjusted by the content of nickel and the carbonization temperatures. The excellent acid-resistant property of the magnetic materials makes them useful in magnetic separation.

Polyaniline (PANI) loaded ordered mesoporous carbon (OMC) composites were prepared via different processes, involving the in situ polymerization of aniline in the presence of OMC or its precursor and the direct physical mixing method. On the basis of analyzing the morphologies and structures of these three OMC/PANI composites, the influence of compounding processes on the electrochemical properties as electrodes for supercapacitors was first investigated. It was observed that regardless of compounding process, two distinct electrochemical behaviors took place on all of the composite electrodes, including a redox reaction with insertion and deinsertion of electrolyte ions, and electrostatic attraction at the electrode/electrolyte interface. Additionally, these OMC/PANI composites showed higher specific capacitances compared with pure OMC and PANI. Most significantly, the in situ synthesized OMC/PANI composite using OMC as a starting material exhibited the highest specific capacitance of 747 F g−1 at a current density of 0.1 A g−1 and excellent rate capability, which was attributed to the high degree of dispersion of PANI and the contact of PANI with electrolyte as well as the double fixing effects of surface and mesopore of OMC on PANI.

Carbon nanotubes capsules (CNCs) with compact, stout walls and tunable sizes were fabricated by using self-assembly of acid modified carbon nanotubes in a water-in-oil emulsion system. The effect of ultrasonic power on the formation and size of CNCs were investigated. On the basis of fabrication of CNCs, CNCs encapsulating SnO2 nanoparticles were prepared as anode material for lithium ion batteries. The morphologies, structural characteristics and electrochemical performances of CNCs and CNCs encapsulating SnO2 nanoparticles were systemically investigated by FE-SEM, TEM, XRD and a series of electrochemical testing techniques. The results showed that the encapsulation amount of SnO2 in CNCs had a great influence on the reversible capacity and cycle performance of the composites. The composite with appropriate amount of SnO2 exhibited a high reversible capacity of 383 mAh g−1 and an excellent cyclability with only 0.4% capacity loss/cycle in that CNCs not only could provide high electric conductivity for composites but also effectively accommodate the volume change of SnO2 during the cycling processes.

Graphene nanosheets (GNSs) were prepared from artificial graphite by oxidation, rapid expansion and ultrasonic treatment. The morphology, structure and electrochemical performance of GNSs as anode material for lithium-ion batteries were systematically investigated by high-resolution transmission electron microscope, scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy and a variety of electrochemical testing techniques. It was found that GNSs exhibited a relatively high reversible capacity of 672 mA h/g and fine cycle performance. The exchange current density of GNSs increased with the growth of cycle numbers exhibiting the peculiar electrochemical performance.

Lepidocrocite TiO2 nanotubes prepared by hydrothermal process were annealed at 300 °C and 500 °C for 1 h in air. The morphologies, structures and electrochemical performances of these TiO2 nanomaterials were investigated by transmission electron microscope, X-ray diffraction and a variety of electrochemical testing techniques. The results showed that the TiO2 nanotubes gradually collapsed during heating period, and were finally transformed into anatase TiO2 nanorods. The electrochemical measurements revealed that all the TiO2 electrodes exhibit a good cycling performance when were used as the anode materials for lithium-ion batteries. Compared with the original TiO2 nanotubes, the 500 °C annealed TiO2 nanomaterial electrode provided a higher first coulombic efficiency and higher lithium-ion transfer rate, implying a promising anode candidate for lithium-ion batteries.

In order to enhance the thermal stability and prepare a new kind of carbon microbeads from poly(divinylbenzene) microspheres (PDM), air oxidation treatment was introduced to modify the pristine PDM. The results showed that the spherical shape of PDM was preserved via the air oxidation and further carbonization at 700 °C. The changes of morphology, especially the surface functional groups and the thermal properties of PDM after air oxidation were investigated in detail by SEM, IR and TG/DSC measurements, respectively. The possible mechanism of oxidation treatment was elucidated.

Highly ordered mesoporous carbon with cubic Im3m symmetry has been synthesized successfully via a direct carbonization of self-assembled F108 (EO132PO50EO132) and resorcinol–formaldehyde (RF) composites obtained in a basic medium of nonaqueous solution.

Tin-based composites using expanded mesocarbon microbeads (EMCMB) as matrix were prepared by impregnating tin chloride and the following reduction under hydrogen atmosphere at different temperatures. The morphologies and structural characteristics of the composites were investigated by FE-SEM, EDS and XRD measurements. It was found that tin exists inside EMCMB in the form of oxidation states (Sn(II) and Sn(IV)) after reduction at lower temperature (below 350 °C), and metallic tin exists both outside EMCMB and between carbon layers after reduction at higher temperature (450 °C). The electrochemical properties of the composites as negative electrode material for lithium-ion batteries were systematically investigated by cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy tests. The results showed that loading amount of tin or tin oxides and reduction temperature had large influences on the reversible capacity and cycle performance of these composites. Among them, the composite reduced at 230 °C with appropriate loading amount of tin oxides not only exhibited the high first reversible gravimetric capacity of 401 mAh g−1 and an excellent cyclability with only 0.2% capacity loss/cycle at lower current density, but also showed a stable cycle performance at higher current density due to its lower resistance.

The effects of etching process on the morphology, structure and electrochemical performance of arc-produced multiwalled carbon nanotubes (CNTs) as anode material for lithium-ion batteries were systematically investigated by TEM and a variety of electrochemical testing techniques. It was found that the etched CNTs exhibited four times higher reversible capacity than that of raw CNTs, and possessed excellent cyclability with almost 100% capacity retention after 30 cycles. The kinetic properties of three kinds of CNTs electrodes involving the pristine (CNTs-1), etched (CNTs-2) as well as etch-carbonized samples (CNTs-3) were characterized via ac impedance measurement. It was indicated that, after 30 cycles the exchange current density i0 of etched CNTs ((7.6–7.8) × 10−3 A cm−2) was higher than that of the raw CNTs (5.9 × 10−3 A cm−2), suggesting the electrochemical activity of CNTs was enhanced by the etching treatment. The storage characteristics of the CNTs electrodes at room temperature and 50 °C were particularly compared. It was found that the film resistance on CNTs electrode generally tended to become large with the elongation of storage time, especially storage at high temperature. In comparison with CNTs-1 and CNTs-3, CNTs-2 exhibited more distinctly increase of film resistance, which is related with the surface properties.

Carbon-encapsulated iron nanoparticles have been synthesized on a large scale by co-carbonization of an aromatic heavy oil and ferrocene at 495 °C under autogenous pressure. In this paper, the effects of heat treatment at 1000 °C on the transformation of morphology and structure of carbon-encapsulated iron nanoparticles were investigated using TEM, HREM and XRD measurements. It was found that the nanoparticles became larger and exhibited various morphologies, e.g. hollow carbon cages and carbon nanotubes, via heat treatment. The disordered carbon shell was transformed into well-ordered graphitic structure under the catalysis of iron core during heat treatment. The transformation mechanism during heat treatment was discussed in detail.

Ordered mesoporous carbon materials were successfully synthesized by the carbonization of sulfuric-acid-treated silica/triblock copolymer/sucrose composites. In the current approach, triblock copolymer P123 and sucrose were employed as both structure-directing agents for self-assembly of tetraethyl orthosilicate and carbon precursors, and sulfuric acid was used to cross-link P123 and sucrose in the as-synthesized composites in order to improve the carbon yield. When the weight ratio of sucrose relative to P123 was 1:4, ordered mesoporous carbon (C-S) with hexagonally arranged pore centered at 3.0 nm was synthesized. However, when the weight ratio was increased to 1:2, the obtained carbon material (C-S-1) exhibited low-ordered pore structure. In addition, thermogravimetric analysis revealed that C-S consisted of ca. 26 wt.% sucrose carbon and ca. 74 wt.% P123 carbon, and there was noticeable interaction between sucrose and P123, where P123 was a key substance for the formation of ordered mesostructure, and sucrose was responsible for the increased carbon yield.

•A new hierarchical porous carbon containing slit-shaped mesopores and 3D carbon nanosheets were prepared using Mg-Al layered double hydroxides as template.•The hierarchical porous carbon electrode showed a high capacity and excellent cycle stability when used in lithium-ion battery.•The excellent performance is ascribed to its hierarchical porous structure, especially the mesoporous struture.Novel hierarchical porous carbons (NHPCs) containing 3D carbon nanosheets and slit-mesopores are prepared in this work, using MgAl-layered double hydroxides as template and sucrose as carbon source, and their electrochemical performances as anodes of lithium-ion batteries are also investigated. Owing to the existence of abundant carbon nanosheets and slit-mesopores, the NHPCs electrode exhibits the specific reversible capacity of 1151.9 mA h/g at the current density of 50 mA/g, which is significantly higher than other hierarchical porous carbons reported in previous literatures. The contributions of carbon nanosheets and mesopores to the electrochemical performance are further clarified by nitrogen adsorption-desorption test, electrochemical impedance spectroscopy, cyclic voltammograms and galvanostatic charge/discharge test. This work not only provides an easy and effective method to prepare hierarchical porous carbon materials, but also is beneficial for the design of high-performance anode materials for lithium ion batteries.

The optional molecular structures and compositions have made metal–organic frameworks (MOFs) an important precursor for preparing functional nanomaterials. In this paper, ZnO nanosheets growing on a MOF-derived porous carbon matrix (ZnO/MPC) were synthesized by in situ pyrolysis of a Zn-based mixed-ligand MOF. The formation of ZnO nanosheets relies on the intermediate structures of the pyrolytic MOFs. The inherent molecular structure and the escape of the ligand molecules will induce the formation of a stacked structure during the heat treatment process, and the layered spaces can provide a directional path for the motion of Zn atoms to the surface of carbon bulk during the pyrolysis of the precursor. This work shows that one can design and synthesize novel nanostructures by controlling the intermediate structures of MOF precursors during the pyrolysis process. The as-synthesized ZnO/MPC also displayed an excellent cyclability and a high reversible capacity of 920 mA h g−1 at a current density of 60 mA g−1, exhibiting a promising prospect in lithium storage application.

For improving the capacity and stability of Sn-based anode materials, a novel Sn–Co nanoalloy embedded in porous N-doped carbon was synthesized using the metal–organic framework ZIF-67 as both the template and carbon source, and SnCl4 as the tin source through carbonization. This composite shows the shape of a microbox with the diameter of about 2 μm in which about 10 nm of Sn–Co nanoalloy particles were uniformly embedded. When used as the anode material for lithium-ion batteries, it exhibits a high capacity of 945 mA h g−1, and 86.6% capacity retention after 100 cycles at 100 mA g−1 as well as an excellent rate capacity of 472 mA h g−1 at a high current density of 2 A g−1. The superior electrochemical performance can be ascribed to the well-dispersed, nano-sized alloy and the buffering effect of porous N-doped carbon coating. Moreover, the uniform particles remain intact upon cycling which gives the material enhanced electrochemical stability.

Graphene nanosheets can be driven to change their conformation by melting metal and, finally, a cocoon coating can be constructed to encapsulate the metal sphere. Interaction beween metal and oxygenated defects plays a leading role in conformational changes of graphene nanosheets.

Highly ordered mesoporous carbon with cubic Im3m symmetry has been synthesized successfully via a direct carbonization of self-assembled F108 (EO132PO50EO132) and resorcinol–formaldehyde (RF) composites obtained in a basic medium of nonaqueous solution.

Mesoporous soft carbon (MSC) was prepared from mesophase pitch using nano-CaCO3 as the template. The crystalline structure of soft carbon consists of a disordered region with a large interlayer distance benefitting sodium ion insertion/extraction and a graphitic region with good electrical conductivity favoring high rate performance. Additionally, the mesoporous structure not only shortens the path of ion diffusion but also facilitates the penetration of non-aqueous electrolytes, which can further enhance the electrochemical performance of MSC. Benefiting from its unique microstructure, the MSC delivers a reversible capacity of 331 mA h g−1 at 30 mA g−1, and retains a capacity of 103 mA h g−1 at 500 mA g−1 after 3000 cycles, indicating its excellent rate capability and cycling performance. Therefore, soft carbon with appropriate structure is expected to be another choice for anode materials of sodium ion batteries.

Novel branched carbon encapsulated MnS (MnS@C) nanochains were prepared by an in situ co-pyrolysis method. The morphology and structure of the MnS@C nanochains were mainly characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). It was found that the prepared MnS@C nanochains possess interesting branched structures, which are constructed by interconnected MnS@C nanoparticles with a diameter of ca. 200–400 nm. More interestingly, the MnS@C nanoparticles have novel “pomegranate-like” structures, in which inner cores are not made of whole nanoparticles but composed of many MnS nanoparticles. The formation mechanism of MnS@C should be attributed to an Oriented Attachment (OA) mechanism by investigating various intermediate products obtained by controlling the reaction conditions. The branched MnS@C nanochains after annealing (MnS@C-800) demonstrated perfect cycling stability and long cycle life when used as anode materials for lithium-ion batteries (LIBs). At a current density of 50 mA g−1, the stable specific capacity is around 545 mA h g−1 while the pure MnS anode experiences a drastic drop quickly to 300 mA h g−1 at the initial few cycles. At 500 mA g−1, the reversible specific capacity is ca. 318 mA h g−1 at the initial cycle and is maintained at ca. 200 mA h g−1 after 800 cycles.

Novel hierarchical porous carbon nanosheets (HPCS) with quantities of micropores and mesopores were prepared on a large-scale by using thermoplastic phenolic formaldehyde resin as the carbon source and copper nitrate as the template precursor. The HPCS, possessing a thickness of about 40 nm and the width of several microns, exhibited a high specific capacity and favorable high-rate performance when used as an anode material for lithium ion batteries (LIBs). The reversible capacities were 748 mA h g−1 at a current density of 20 mA g−1 and 460 mA h g−1 even at 1 A g−1, which were much higher than those of traditional porous carbon materials. It also showed superior cyclical stability for only 0.3% capacity loss per cycle under high rate charge-discharge process, suggesting that HPCS should be a promising candidate for anode materials in high-rate LIBs. The roles of various-sized pores in HPCS in Li storage were discussed briefly.

Graphene nanosheets (GNSs) loading graphene-encapsulated iron microspheres (GEIMs) were fabricated by heat treatment of graphene oxide nanosheets (GONs) with ferric trichloride (FeCl3). The special pentagon-hexagonal graphene shells have been produced by precipitation of carbon from metal carbide solutions, thanks to the high reactivity of GONs and ferric nanoparticles dispersing homogeneously between graphene layers. The morphology, structure and elemental composition of GEIMs were investigated by scanning electron microscope, X-ray diffraction and electron energy disperse spectroscope, respectively. The formation mechanism of GEIMs was proposed. Hollow graphene microspheres (HGMs) on the GNSs were obtained with the removal of ferric species in GEIMs. When used as the anode materials for lithium-ion batteries, the almost graphitic HGMs exhibit stable voltage platform at ca. 0.2 V, excellent cycle capability and higher reversible capacity of about 440 mAh g−1 after 50 cycles and possess great potential application in lithium–ion batteries.

In order to strengthen the nanostructure and suppress the collapse of nanopores of resorcinol–formaldehyde (RF) aerogels during the drying process, graphene oxide (GO) was incorporated into the RF matrix to prepare GO–RF composite aerogels by sol–gel polymerization. The influences of GO content on the sol–gel process, structure, and physical properties of RF aerogels were investigated. The morphologies of composite aerogels were characterized by scanning electron microscopy and transmission electron microscopy, and it was found that GO was well dispersed in the RF matrix. In addition, GO can obviously accelerate the gelation of the RF solution and reduce both the drying shrinkage and aerogel density. As the content of GO increased from 0 to 2 wt%, both the linear shrinkage and density of composite aerogels decreased progressively from 28.3% to 2.0% and 506 to 195 kg m−3, respectively, implying that GO is an effective additive for inhibiting the volume shrinkage of aerogels during the drying process.

A novel and effective route for preparing phenol formaldehyde resin grafted reduced graphene oxide (rGO-g-PF) electrode materials with highly enhanced electrochemical properties is reported. In order to prepare rGO-g-PF, hydroxymethyl-terminated PF is initially grafted to graphene oxide (GO) via esterification reaction. Subsequently, the grafted GO is reduced by the carbonization process under an inert gas atmosphere. The covalent linkage, morphology, thermal stability and electrochemical properties of rGO-g-PF are systematically investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, thermal gravimetric analysis, differential scanning calorimetry and a variety of electrochemical testing techniques. In the constructed architecture, the amorphous carbon shell can inhibit the co-intercalation of solvated lithium ion and avoid partial exfoliation of the graphene layers, thus effectively reducing the irreversible capacity and preserving the structural integrity. Meanwhile, the carbon coating layer leading to a decreased thickness of SEI film can improve the conductivity of electrode materials. As a result, the rGO-g-PF electrode exhibits impressive high cycling stability at various large current densities (376.5 mA h g−1 at 50 mA g−1 for 250 cycles, 337.8 mA h g−1 at 200 mA g−1 and 267.8 mA h g−1 at 1 A g−1 for 200 cycles), in combination with high rate capability.

A novel spherical ordered mesoporous carbon with a high surface area and cage-type porous structure was prepared by direct carbonization of silica/triblock copolymer/butanol composite using F127 and butanol as both structure-directing agent and carbon precursor.

Hollow graphene oxide spheres (HGOSs) were fabricated from graphene oxide nanosheets (GONs) utilizing a water-in-oil (W/O) emulsion technique without surfactant. Effects of oxidation treatment and water removal on the formation and morphology of HGOSs are investigated. The oxidation time for preparing GONs is a crucial factor for the formation and morphology of HGOSs. We found that with increasing oxidation time, the morphology and surface topography of HGOSs vary from irregular and rough to uniform and smooth shape with decreasing diameter. Moreover, the electrochemical performance of HGOSs as anode materials in lithium-ion batteries was evaluated. The heat-treated HGOSs exhibit a 485 mAh g−1 reversible capacity and high rate performance thanks to the hollow structure, thin and porous shells consisting of graphene.

Novel carbon nanotubes (CNTs) were prepared on a large-scale. Their morphology and structure were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman measurements. It was found that the prepared CNTs possess a quadrangular cross section, as well as one open end and “herringbone”-like walls, so these novel CNTs were named q-CNTs. The unique morphology of q-CNTs implies broad potential applications in many fields, including drug delivery, conductive and high-strength composites, field emission displays and radiation sources, hydrogen storage media, and supercapacitors. When used as the anode materials for lithium-ion batteries, q-CNTs exhibit excellent high-rate performance (a high-reversible capacity of 181 mAh g−1 at the current density of 1000 mA g−1 (ca. 3 C)), which is much higher than that of the common multi-wall carbon nanotubes. This high-rate performance should be attributed to the unique nanostructure of q-CNTs, which results in a high diffusion coefficient for lithium ions in the q-CNTs.

A novel flat cake-type ordered mesoporous carbon was directly prepared by a one-step hard templating method simultaneously using the nonionic surfactant Pluronic P123 (EO20PO70EO20) and cationic surfactant cetyltrimethylammonium bromide (CTAB) as both the structure-directing agent and carbon precursor.

Solution-based oxidation has been widely utilized to prepare graphene oxide or graphene nanoribbons from different carbon precursors, but some details of the exfoliation or unzipping processes still remain elusive. Here, we put forward three graphitic systems for deep understanding of the top-down route. Based on the oxidation-intercalation synergistic effect, the formation mechanisms were proposed.

Ordered mesoporous carbons with various morphologies, including rod-like, gyroid-shaped, plate-like and flower-type, were synthesized by changing the hydrochloric acid concentration in the formation of silica/triblock copolymer P123/glycerol composites and further carbonization. Triblock copolymer P123 and glycerol were used as both the structure-directing agents and the carbon precursors. The morphologies, structures and pore characteristics of the carbon materials were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen sorption techniques. The electrochemical performances of the carbons as electrodes for supercapacitors were measured. The relationships between the capacitive behavior, the morphology and the pore characteristics were elucidated briefly. It was found that the sample possessing the highest surface area of 1312 m2 g−1 exhibits the highest specific capacity of 164 F g−1 among the five samples at a current density of 100 mA g−1, and decreases from 164 to 142 F g−1 with an increase in current density from 100 to 2000 mA g−1. The capacitance retention ratio (relative to the capacitance at a current density of 100 mA g−1) of the sample with short rods at a current density of 2000 mA g−1 (94.4%) is much higher than that of the sample with long rods (86.6%), which could be partly ascribed to its shorter pore channels.

Due to its inert closed-shell structure, the graphitic onion-like carbon (GOC) could not be exfoliated into a graphene-like structure by a simple Hummers' method even under rigorous conditions. Herein, we successfully exfoliated GOC into twisted graphene oxide nanosheets by the cooperation of chemical activation and Hummers' oxidation. Porphyra-like graphene nanosheets were further prepared from the twisted graphene oxide nanosheets by rapid thermal expansion. The defects introduced by activation were considered to play significant roles in the unfolding of GOC because they provide reactive sites for the oxidation. As an anode material for lithium ion batteries, the obtained porphyra-like graphene exhibited much better electrochemical properties than those of GOC. Our work can contribute to (1) deeply understand the exfoliation mechanism of graphitic materials by chemical oxidation especially the influence of defects during these steps; and (2) provide new strategies for designing functional graphene based materials from inert graphitic structures.

Cobalt hydroxide arrays/graphene nanosheets (Co(OH)2 array/GNSs) composites are formed by the growth of preferential-orientation versus basal planes of GNSs. Notably, the Co(OH)2 nanoplates, possessing special hexagonal morphology with the length of about 130 nm and average thickness of about 20 nm, stand vertically rather than lie flat on the surface of graphene sheets. More interestingly, the (001) crystal plane of Co(OH)2 is vertical to the graphene basal plane and forms strong covalent bond interaction (Co–C bond) with the graphene layer, which could be a driving force for the preferential growth of nanoarrays on graphene. Co(OH)2 array/GNSs composites exhibit not only high specific capacity, but also outstanding high-rate performance when used as anode materials for lithium-ion batteries. At the current density of 50 mA g−1, the reversible capacity is 976 mA h g−1 and remains at 1103 mA h g−1 after 50 cycles without any fading. At 500 and 1000 mA g−1, the reversible capacities can reach 696 and 496 mA h g−1, which are 71% and 51% of that at 50 mA g−1, respectively. Excellent electrochemical performance could be attributed to the array structure of Co(OH)2 as well as a synergistic effect between Co(OH)2 and graphene. Therefore, Co(OH)2 array/GNSs composites are expected to have potential applications in LIBs.

NH2-terminated Si nanoparticles with an ultrathin silica shell have been efficiently obtained by a one-step reaction in ammonia–water–ethanol solution. Graphene nanosheet (GNS) encapsulated Si@ultrathin SiOx has been fabricated by self-assembly and thermal treatment. Because of the uniform ultrathin SiOx shell and superior GNS encapsulation structure, this material shows a reversible capacity of 2391.3 mA h g−1, maintaining 1844.9 mA h g−1 after 50 cycles at a current density of 200 mA g−1, and good rate and long cycle performance (∼700 mA h g−1 at 2000 mA g−1 after 350 cycles) as well.

Porous graphene films (PGFs) were developed by introducing defects and extra edges into graphene using GO and a metal salt (ferric nitrate) as sources via a facile filtration method together with a thermal reduction and subsequent removal of the metal. The pore size and density could be controlled by simply adjusting the amount of ferric nitrate. When used as an anode for lithium ion batteries, PGF-1 showed a high reversible capacity, improved cycling stability, and ultra-high rate performance (971, 298, and 163 mA h g−1 at the rates of 10, 30, and 50 A g−1 after 10000 cycles). When used as an anode for sodium ion batteries, PGF-1 showed a reversible capacity of 195 mA h g−1 at 50 mA g−1 after 50 cycles. Even at a high rate of 1000 mA g−1, the reversible capacity can still remain at 111 mA h g−1 after 1000 cycles. The excellent performance should be attributed to the special porous structure of the PGF. On one hand, plenty of defects within the PGF provided extra reaction sites for lithium and sodium ion storage. On the other hand, the porous structure of the PGF resulted in fast diffusion and transfer of lithium/sodium ions and electrons throughout the electrodes.

Iron sulfide-embedded carbon microspheres were prepared via a solvothermal process and show high specific capacity and excellent high-rate performance as anode material for lithium-ion batteries.