Coexistence of metallic and semiconducting carbon nanotubes has often been a bottleneck in many a... more Coexistence of metallic and semiconducting carbon nanotubes has often been a bottleneck in many applications and much fundamental research. Single-walled carbon nanotubes (SWCNTs) were dissolved in HNO 3 /H 2 SO 4 mixture to confirm differing reactivity between metallic (m) and semiconducting (s) SWCNTs. With HNO 3 / H 2 SO 4 treatment, s-SWCNTs remained intact, while m-SWCNTs were completely removed for SWCNTs with small diameters less than 1.1 nm, which was confirmed by resonant Raman and optical absorption spectra. We also showed that nitronium ions (NO 2 +) dissolved in the HNO 3 /H 2 SO 4 solution could preferably attack the m-SWCNTs, which was supported by our theoretical calculation. This clear selectivity can be explained by the preferential adsorption of positively charged NO 2 + on m-SWCNTs due to more available electron densities at the Fermi level in the m-SWCNTs. We report for the first time a selective removal of smalldiameter m-SWCNTs by using HNO 3 /H 2 SO 4 solution, which presented a striking contrast to the diameterselective removal of SWCNTs by oxidative etching reported previously.
PAN/pitch-based carbon nanofiber/MnO 2 (PPMn-CNF) composites are fabricated by electrospinning to... more PAN/pitch-based carbon nanofiber/MnO 2 (PPMn-CNF) composites are fabricated by electrospinning to obtain a new type of electrode material for application in high-capacitance electrical double-layer capacitors (EDLCs). The energy storage capabilities of these PPMn-CNFs reveal a maximum specific capacitance of 188 Fg-1 and a maximum energy density of 20.5-15.8 Whkg-1 in the power density range of 400-10,000 Wkg-1. Furthermore, the PPMn-CNF electrode shows good rate capability without a significant decrease at high rate. The high electrical conductivity of the pitch promotes the accessibility into the micropores and the adsorption efficiency onto the electrode surface of electrolyte ions. Therefore, the high electrical conductivity and large surface area of the PPMn-CNF composites are beneficial for the storage of charge carriers and induce a short course for charge transport, which maximizes the specific capacitance and ensures good capacitive capability.
Si-based Li-ion battery (LIB) anode materials often possess porous structures to accommodate the ... more Si-based Li-ion battery (LIB) anode materials often possess porous structures to accommodate the intrinsic volumetric expansion of Si upon cycling. However, the porous structure may cause poor initial coulombic efficiency (ICE), inadequate cycle life due to the continuous generation of a solid-electrolyte interface, and incompatibility with calendaring processes. To overcome these issues, we designed an optimized Si/C (P-Si/C) composite anode consisting of Si nanoparticles, graphite, and pitch, with a highly densified structure, suppressing Si expansion and enabling compatibility with the calendaring process. To further enhance the cycle life, the surface of the P-Si/C composite was modified by chemical vapor deposition using CH 4 gas (C-Si/C). The P-Si/C anode exhibited a high ICE of 88.0% with a rapid surge up to 99.0% after only the 4th cycle. The C-Si/C anode presented an improved capacity retention of 49.5% after the 39th cycle, compared with 46.0% for the P-Si/C anode after the 31st cycle, while maintaining the same ICE. Moreover, anodes prepared with 8 wt% P-Si/
Recently, some studies have utilized silicon (Si) as an anode material of lithium ion battery by ... more Recently, some studies have utilized silicon (Si) as an anode material of lithium ion battery by recycling Si from the slurry of wafer slicing dust. The filtration of Si particles condensed from Si vapors that were exhausted from the ingot growing furnace could propose another method of Si recycling. In this study, we investigated the possibility of using such collected silicon oxides (SiOx) particles as an anode material. After collecting SiOx particles, FE-SEM, TEM, EDS, XRD, XPS analysis, and charge/discharge test were carried out to investigate characteristics and usability of these particles. FE-SEM and FE-TEM images showed that these particles mainly consisted of spherical primary particles with a diameter of 10 nm or less. Agglomerates of these primary particles were larger than 300 nm in diameter. In TEM image and EDS analysis, crystalline particles were observed along with amorphous particles. As a result of XRD analysis, amorphous silica (SiO2) and crystalline Si were obse...
The objective of this study is to fabricate conductive carbon fiber composites with thermal and e... more The objective of this study is to fabricate conductive carbon fiber composites with thermal and electrical properties by degradation carbon-fiber-reinforced plastics (CFRPs) and recycled carbon fibers using only supercritical water without any catalyst or oxidant. We focused on a recycling method that is harmless to the human body and environment-friendly, by using supercritical fluid water rather than recycling CFRP by physical or pyrolysis methods. In particular, we recycled carbon fibers (R-CFs) in which up to 99.5% of epoxy resin was removed, by optimizing the conditions of supercritical fluid water (SCF-W) treatment, and we fabricated conductive R-CFs composites with thermal and electrical properties by combining the R-CFs with cyclic butylene terephthalate (CBT), which is a polymerizable low-viscosity thermoplastic resin. The fabricated composites had a thermal conductivity of 1.35 ± 0.05 (W/mK) and an electrical conductivity of 11.23 × 10 −6 (S/cm) when the added amount of recycled carbon fibers was 5 wt%.
Flexible transparent conducting films (TCFs) were fabricated by dip-coating single-wall carbon na... more Flexible transparent conducting films (TCFs) were fabricated by dip-coating single-wall carbon nanotubes (SWCNTs) onto a flexible polyethylene terephthalate (PET) film. The amount of coated SWCNTs was controlled simply by dipping number. Because the performance of SWCNT-based TCFs is influenced by both electrical conductance and optical transmittance, we evaluated the film performance by introducing a film property factor using both the number of interconnected SWCNT bundles at intersection points, and the coverage of SWCNTs on the PET substrate, in field emission scanning electron microscopic images. The microscopic film property factor was in an excellent agreement with the macroscopic one determined from electrical conductance and optical transmittance measurements, especially for a small number of dippings. Therefore, the most crucial factor governing the performance of the SWCNT-based TCFs is a SWCNT-network structure with a large number of intersection points for a minimum amount of deposited SWCNTs.
This paper investigated the fracture behavior of the unavoidable breakage of carbon fibers and fi... more This paper investigated the fracture behavior of the unavoidable breakage of carbon fibers and fiber orientation of short carbon fiber reinforced polycarbonate composite in injection process. In this experiment, short carbon fiber mixed compound of 1mm, 3mm, 5mm, 7mm length with 10wt.%, 15wt.%, 20wt.% in polycarbonate for injection molding were produced through the extruder. The dumbbell specimens for tensile evaluation were made by injection molding. The parent specimens were made by double gate method, the weld specimens were made by single gate method which was controlled by inserting a stopper through the runner of the mold cavity. Short carbon fiber reinforced PC composite was evaluated by micro-CT with regard to the particle size of short fiber with a diversified quantitative analysis through entire process of the injection process in composite. The quantitative distribution of fiber orientation was also examined by micro-CT with regard to normal direction or anisotropy. Weld ...
Journal of colloid and interface science, Jan 15, 2015
Nanoporous carbons, with different micropore size distributions, were prepared based on waste cof... more Nanoporous carbons, with different micropore size distributions, were prepared based on waste coffee grounds by a chemical activation process in order to elucidate the correlation between desolvated ions and pores smaller than the sizes of ions using an organic electrolyte. The pore structure of the coffee-based nanoporous carbon was strongly dependent on the heat-treatment temperature prior to the activation process. Cyclic voltammograms of the nanoporous carbons mainly dominated by the smaller pore relative to that of the bare ion size clearly showed deviation from an ideal feature of the current response. It was clearly envisaged that even a bare ion of a size larger than the pore size can penetrate into the pore by voltage-induced force.
We have introduced a new approach to selectively remove metallic single-walled carbon nanotubes ͑... more We have introduced a new approach to selectively remove metallic single-walled carbon nanotubes ͑SWCNTs͒ using a gas phase reaction by fluorine gas, followed by a heat treatment. The metallicity of the treated samples was characterized by the resonant Raman spectra with three wavelengths of 514, 633, and 785 nm and UV-visible-NIR absorption spectra. Peaks of metallic SWCNTs with small diameters less than 1.1 nm in the radial breathing mode of Raman spectra were greatly suppressed with fluorination and completely disappeared after heat treatment. On the other hand, the semiconducting SWCNTs with small diameters less than 1.1 nm were still retained after fluorination. Moreover, the D-band decreased after annealing at 900°C, which was associated with the release of fluorine atoms during heat treatment. The removal of metallic SWCNTs was not observed at SWCNTs with diameters greater than 1.1 nm. The absorption data also demonstrated the similar diameter dependence in the selectivity to the Raman spectra.
We have investigated the structural transformation of fluorinated singlewalled nanotubes (SWNTs) ... more We have investigated the structural transformation of fluorinated singlewalled nanotubes (SWNTs) induced by electron-beam irradiation during the transmission electron microscope observations. Heavily fluorinated SWNT bundles were systematically transformed into multiwall-like nanotubes by releasing fluorine atoms during electron-beam irradiation and even broken into two pieces of the capped graphitic structures. Such structural transformations at relatively low kinetic energy (e300 keV) could be explained by the local strains induced by fluorination, where CC bonds that were fluorine-attached became 1.53 Å, a single bond similar to that of a diamond, from our density functional calculations. We propose a possible concerted pathway for the structural transformation of fluorinated SWNTs induced by electron-beam irradiation based on the experimental observations.
The field emission characteristics of patterned carbon nanotubes (CNTs) the average diameter of w... more The field emission characteristics of patterned carbon nanotubes (CNTs) the average diameter of which is 16 nm cathodes on substrates with different surface treatments were investigated. The surface treatments of the substrate were performed by nickel electroless plating and palladium coating, which is an activation procedure of electroless plating. CNTs were patterned on the surface-treated substrate with radius of 200 lm through conventional photolithography process. Two deposition methods, electrophoresis deposition and spray deposition, were used to investigate the effects of deposition methods on field emission characteristics of the cathodes. It was revealed that the two deposition methods showed similar turn-on field trends, which means that the different surface morphologies of the substrates have more influence on the field emission characteristics than the different deposition methods performed in this study. Through the surface treatments, the roughness of the surface increased and cathodes with a high roughness factor showed better field emission characteristics compared to non-treated ones.
Carbon-coated Si/carbon nanotube/graphene oxide (C-Si/CNT/GO) microspheres with a robust core–she... more Carbon-coated Si/carbon nanotube/graphene oxide (C-Si/CNT/GO) microspheres with a robust core–shell composite structure were successfully fabricated by efficient and scalable spray-drying and chemical vapor deposition (CVD) for application as a lithium-ion battery (LIB) anode. The amphiphilic GO nanoparticles facilitated the uniform dispersion of Si nanoparticles by suppressing the CNT aggregation in the Si/CNT/GO microspheres, efficiently forming a robust Si/CNT/GO microsphere composite structure. The surface of the Si/CNT/GO microsphere composite was coated with carbon using CH4 via CVD to enhance its cycling performance. The four building block components, namely, Si nanoparticles, CNTs, and GO nanoparticles as the core and the carbon-coating layers as the shell, provided high electrochemical capacity, excellent electrical conductivity, efficient buffer space for the volume expansion of the Si nanoparticles, and high structural stability during lithiation/delithiation. The C-Si/C...
There is an urgent need to develop improved anode materials for lithium-ion batteries (LIBs). Her... more There is an urgent need to develop improved anode materials for lithium-ion batteries (LIBs). Herein, we report the synthesis of a graphene quantum dots (GQDs)-coated hierarchical nanoflake-based CuO microspheres (H-CuO) composite on Cu foam via a one-pot hydrothermal technique for use as a binder-free anode for LIBs. The carboxyl-functionalized GQD coating on H-CuO not only results in lower charge-transfer resistance and enhanced electrical conductivity but also prevents the dissolution and agglomeration of the electrode. The GQDs/H-CuO composite anode exhibits a reversible capacity as high as 609 mAh g − 1 (pristine H-CuO: 61 mAh g − 1) after 200 cycles at 0.2 A g − 1. It also shows long-term cycling stability, exhibiting a capacity retention rate of 79.4% after 1000 cycles (pristine H-CuO: 0.7%) at a high current density (2 A g − 1) and improved initial coulombic efficiency at 88.2% (pristine H-CuO: 75.2%). The superior electrochemical properties of the GQDs/ H-CuO composite anode are attributable to the graphene networks, which help maintain a high specific surface area and effectively protect the anodic active material from forming an unstable solid electrolyte interface layer. The proposed strategy for fabricating the GQD-coated metal oxide microsphere-based anode should contribute to the development of next-generation LIBs with improved electrochemical performance.
Densely packed assemblies of single-walled carbon nanotubes (SWCNTs) were characterized by N 2 an... more Densely packed assemblies of single-walled carbon nanotubes (SWCNTs) were characterized by N 2 and CO 2 adsorption techniques. We presented a convenient method for forming densely packed assembly structures of SWCNTs. The SWCNTs were treated with mixtures of HNO 3 /H 2 SO 4 or H 2 O 2 /H 2 SO 4 before and after purification, to control the packing density and porosity of the SWCNT samples. H 2 O 2 /H 2 SO 4 treatment caused a dramatic increase in microporosity without significantly changing the mesoporosity, whereas HNO 3 /H 2 SO 4 treatment decreased the mesoporosity and simultaneously increased the microporosity. This reduced mesoporosity originates from the contraction of the interbundle distance of SWCNTs. After HNO 3 /H 2 SO 4 treatment of the purified SWCNTs, the micropore surface area increased about 8.6 times compared to the pristine sample, and the volume fraction of the micropores increased from 10% to 91%, indicating formation of densely packed assemblies of SWCNTs. Therefore, HNO 3 /H 2 SO 4 treatment could control not only the SWCNT bundle size but also the interbundle distance of the SWCNTs. Moreover, the purification is of importance in promoting the formation of densely packed SWCNTs. We also demonstrated that acid treatments could develop narrow micropores, which was evidenced by CO 2 adsorption at 273 K. We emphasize that this approach can simply control the packing density as well as the porosity of SWCNT assemblies.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Coexistence of metallic and semiconducting carbon nanotubes has often been a bottleneck in many a... more Coexistence of metallic and semiconducting carbon nanotubes has often been a bottleneck in many applications and much fundamental research. Single-walled carbon nanotubes (SWCNTs) were dissolved in HNO 3 /H 2 SO 4 mixture to confirm differing reactivity between metallic (m) and semiconducting (s) SWCNTs. With HNO 3 / H 2 SO 4 treatment, s-SWCNTs remained intact, while m-SWCNTs were completely removed for SWCNTs with small diameters less than 1.1 nm, which was confirmed by resonant Raman and optical absorption spectra. We also showed that nitronium ions (NO 2 +) dissolved in the HNO 3 /H 2 SO 4 solution could preferably attack the m-SWCNTs, which was supported by our theoretical calculation. This clear selectivity can be explained by the preferential adsorption of positively charged NO 2 + on m-SWCNTs due to more available electron densities at the Fermi level in the m-SWCNTs. We report for the first time a selective removal of smalldiameter m-SWCNTs by using HNO 3 /H 2 SO 4 solution, which presented a striking contrast to the diameterselective removal of SWCNTs by oxidative etching reported previously.
PAN/pitch-based carbon nanofiber/MnO 2 (PPMn-CNF) composites are fabricated by electrospinning to... more PAN/pitch-based carbon nanofiber/MnO 2 (PPMn-CNF) composites are fabricated by electrospinning to obtain a new type of electrode material for application in high-capacitance electrical double-layer capacitors (EDLCs). The energy storage capabilities of these PPMn-CNFs reveal a maximum specific capacitance of 188 Fg-1 and a maximum energy density of 20.5-15.8 Whkg-1 in the power density range of 400-10,000 Wkg-1. Furthermore, the PPMn-CNF electrode shows good rate capability without a significant decrease at high rate. The high electrical conductivity of the pitch promotes the accessibility into the micropores and the adsorption efficiency onto the electrode surface of electrolyte ions. Therefore, the high electrical conductivity and large surface area of the PPMn-CNF composites are beneficial for the storage of charge carriers and induce a short course for charge transport, which maximizes the specific capacitance and ensures good capacitive capability.
Si-based Li-ion battery (LIB) anode materials often possess porous structures to accommodate the ... more Si-based Li-ion battery (LIB) anode materials often possess porous structures to accommodate the intrinsic volumetric expansion of Si upon cycling. However, the porous structure may cause poor initial coulombic efficiency (ICE), inadequate cycle life due to the continuous generation of a solid-electrolyte interface, and incompatibility with calendaring processes. To overcome these issues, we designed an optimized Si/C (P-Si/C) composite anode consisting of Si nanoparticles, graphite, and pitch, with a highly densified structure, suppressing Si expansion and enabling compatibility with the calendaring process. To further enhance the cycle life, the surface of the P-Si/C composite was modified by chemical vapor deposition using CH 4 gas (C-Si/C). The P-Si/C anode exhibited a high ICE of 88.0% with a rapid surge up to 99.0% after only the 4th cycle. The C-Si/C anode presented an improved capacity retention of 49.5% after the 39th cycle, compared with 46.0% for the P-Si/C anode after the 31st cycle, while maintaining the same ICE. Moreover, anodes prepared with 8 wt% P-Si/
Recently, some studies have utilized silicon (Si) as an anode material of lithium ion battery by ... more Recently, some studies have utilized silicon (Si) as an anode material of lithium ion battery by recycling Si from the slurry of wafer slicing dust. The filtration of Si particles condensed from Si vapors that were exhausted from the ingot growing furnace could propose another method of Si recycling. In this study, we investigated the possibility of using such collected silicon oxides (SiOx) particles as an anode material. After collecting SiOx particles, FE-SEM, TEM, EDS, XRD, XPS analysis, and charge/discharge test were carried out to investigate characteristics and usability of these particles. FE-SEM and FE-TEM images showed that these particles mainly consisted of spherical primary particles with a diameter of 10 nm or less. Agglomerates of these primary particles were larger than 300 nm in diameter. In TEM image and EDS analysis, crystalline particles were observed along with amorphous particles. As a result of XRD analysis, amorphous silica (SiO2) and crystalline Si were obse...
The objective of this study is to fabricate conductive carbon fiber composites with thermal and e... more The objective of this study is to fabricate conductive carbon fiber composites with thermal and electrical properties by degradation carbon-fiber-reinforced plastics (CFRPs) and recycled carbon fibers using only supercritical water without any catalyst or oxidant. We focused on a recycling method that is harmless to the human body and environment-friendly, by using supercritical fluid water rather than recycling CFRP by physical or pyrolysis methods. In particular, we recycled carbon fibers (R-CFs) in which up to 99.5% of epoxy resin was removed, by optimizing the conditions of supercritical fluid water (SCF-W) treatment, and we fabricated conductive R-CFs composites with thermal and electrical properties by combining the R-CFs with cyclic butylene terephthalate (CBT), which is a polymerizable low-viscosity thermoplastic resin. The fabricated composites had a thermal conductivity of 1.35 ± 0.05 (W/mK) and an electrical conductivity of 11.23 × 10 −6 (S/cm) when the added amount of recycled carbon fibers was 5 wt%.
Flexible transparent conducting films (TCFs) were fabricated by dip-coating single-wall carbon na... more Flexible transparent conducting films (TCFs) were fabricated by dip-coating single-wall carbon nanotubes (SWCNTs) onto a flexible polyethylene terephthalate (PET) film. The amount of coated SWCNTs was controlled simply by dipping number. Because the performance of SWCNT-based TCFs is influenced by both electrical conductance and optical transmittance, we evaluated the film performance by introducing a film property factor using both the number of interconnected SWCNT bundles at intersection points, and the coverage of SWCNTs on the PET substrate, in field emission scanning electron microscopic images. The microscopic film property factor was in an excellent agreement with the macroscopic one determined from electrical conductance and optical transmittance measurements, especially for a small number of dippings. Therefore, the most crucial factor governing the performance of the SWCNT-based TCFs is a SWCNT-network structure with a large number of intersection points for a minimum amount of deposited SWCNTs.
This paper investigated the fracture behavior of the unavoidable breakage of carbon fibers and fi... more This paper investigated the fracture behavior of the unavoidable breakage of carbon fibers and fiber orientation of short carbon fiber reinforced polycarbonate composite in injection process. In this experiment, short carbon fiber mixed compound of 1mm, 3mm, 5mm, 7mm length with 10wt.%, 15wt.%, 20wt.% in polycarbonate for injection molding were produced through the extruder. The dumbbell specimens for tensile evaluation were made by injection molding. The parent specimens were made by double gate method, the weld specimens were made by single gate method which was controlled by inserting a stopper through the runner of the mold cavity. Short carbon fiber reinforced PC composite was evaluated by micro-CT with regard to the particle size of short fiber with a diversified quantitative analysis through entire process of the injection process in composite. The quantitative distribution of fiber orientation was also examined by micro-CT with regard to normal direction or anisotropy. Weld ...
Journal of colloid and interface science, Jan 15, 2015
Nanoporous carbons, with different micropore size distributions, were prepared based on waste cof... more Nanoporous carbons, with different micropore size distributions, were prepared based on waste coffee grounds by a chemical activation process in order to elucidate the correlation between desolvated ions and pores smaller than the sizes of ions using an organic electrolyte. The pore structure of the coffee-based nanoporous carbon was strongly dependent on the heat-treatment temperature prior to the activation process. Cyclic voltammograms of the nanoporous carbons mainly dominated by the smaller pore relative to that of the bare ion size clearly showed deviation from an ideal feature of the current response. It was clearly envisaged that even a bare ion of a size larger than the pore size can penetrate into the pore by voltage-induced force.
We have introduced a new approach to selectively remove metallic single-walled carbon nanotubes ͑... more We have introduced a new approach to selectively remove metallic single-walled carbon nanotubes ͑SWCNTs͒ using a gas phase reaction by fluorine gas, followed by a heat treatment. The metallicity of the treated samples was characterized by the resonant Raman spectra with three wavelengths of 514, 633, and 785 nm and UV-visible-NIR absorption spectra. Peaks of metallic SWCNTs with small diameters less than 1.1 nm in the radial breathing mode of Raman spectra were greatly suppressed with fluorination and completely disappeared after heat treatment. On the other hand, the semiconducting SWCNTs with small diameters less than 1.1 nm were still retained after fluorination. Moreover, the D-band decreased after annealing at 900°C, which was associated with the release of fluorine atoms during heat treatment. The removal of metallic SWCNTs was not observed at SWCNTs with diameters greater than 1.1 nm. The absorption data also demonstrated the similar diameter dependence in the selectivity to the Raman spectra.
We have investigated the structural transformation of fluorinated singlewalled nanotubes (SWNTs) ... more We have investigated the structural transformation of fluorinated singlewalled nanotubes (SWNTs) induced by electron-beam irradiation during the transmission electron microscope observations. Heavily fluorinated SWNT bundles were systematically transformed into multiwall-like nanotubes by releasing fluorine atoms during electron-beam irradiation and even broken into two pieces of the capped graphitic structures. Such structural transformations at relatively low kinetic energy (e300 keV) could be explained by the local strains induced by fluorination, where CC bonds that were fluorine-attached became 1.53 Å, a single bond similar to that of a diamond, from our density functional calculations. We propose a possible concerted pathway for the structural transformation of fluorinated SWNTs induced by electron-beam irradiation based on the experimental observations.
The field emission characteristics of patterned carbon nanotubes (CNTs) the average diameter of w... more The field emission characteristics of patterned carbon nanotubes (CNTs) the average diameter of which is 16 nm cathodes on substrates with different surface treatments were investigated. The surface treatments of the substrate were performed by nickel electroless plating and palladium coating, which is an activation procedure of electroless plating. CNTs were patterned on the surface-treated substrate with radius of 200 lm through conventional photolithography process. Two deposition methods, electrophoresis deposition and spray deposition, were used to investigate the effects of deposition methods on field emission characteristics of the cathodes. It was revealed that the two deposition methods showed similar turn-on field trends, which means that the different surface morphologies of the substrates have more influence on the field emission characteristics than the different deposition methods performed in this study. Through the surface treatments, the roughness of the surface increased and cathodes with a high roughness factor showed better field emission characteristics compared to non-treated ones.
Carbon-coated Si/carbon nanotube/graphene oxide (C-Si/CNT/GO) microspheres with a robust core–she... more Carbon-coated Si/carbon nanotube/graphene oxide (C-Si/CNT/GO) microspheres with a robust core–shell composite structure were successfully fabricated by efficient and scalable spray-drying and chemical vapor deposition (CVD) for application as a lithium-ion battery (LIB) anode. The amphiphilic GO nanoparticles facilitated the uniform dispersion of Si nanoparticles by suppressing the CNT aggregation in the Si/CNT/GO microspheres, efficiently forming a robust Si/CNT/GO microsphere composite structure. The surface of the Si/CNT/GO microsphere composite was coated with carbon using CH4 via CVD to enhance its cycling performance. The four building block components, namely, Si nanoparticles, CNTs, and GO nanoparticles as the core and the carbon-coating layers as the shell, provided high electrochemical capacity, excellent electrical conductivity, efficient buffer space for the volume expansion of the Si nanoparticles, and high structural stability during lithiation/delithiation. The C-Si/C...
There is an urgent need to develop improved anode materials for lithium-ion batteries (LIBs). Her... more There is an urgent need to develop improved anode materials for lithium-ion batteries (LIBs). Herein, we report the synthesis of a graphene quantum dots (GQDs)-coated hierarchical nanoflake-based CuO microspheres (H-CuO) composite on Cu foam via a one-pot hydrothermal technique for use as a binder-free anode for LIBs. The carboxyl-functionalized GQD coating on H-CuO not only results in lower charge-transfer resistance and enhanced electrical conductivity but also prevents the dissolution and agglomeration of the electrode. The GQDs/H-CuO composite anode exhibits a reversible capacity as high as 609 mAh g − 1 (pristine H-CuO: 61 mAh g − 1) after 200 cycles at 0.2 A g − 1. It also shows long-term cycling stability, exhibiting a capacity retention rate of 79.4% after 1000 cycles (pristine H-CuO: 0.7%) at a high current density (2 A g − 1) and improved initial coulombic efficiency at 88.2% (pristine H-CuO: 75.2%). The superior electrochemical properties of the GQDs/ H-CuO composite anode are attributable to the graphene networks, which help maintain a high specific surface area and effectively protect the anodic active material from forming an unstable solid electrolyte interface layer. The proposed strategy for fabricating the GQD-coated metal oxide microsphere-based anode should contribute to the development of next-generation LIBs with improved electrochemical performance.
Densely packed assemblies of single-walled carbon nanotubes (SWCNTs) were characterized by N 2 an... more Densely packed assemblies of single-walled carbon nanotubes (SWCNTs) were characterized by N 2 and CO 2 adsorption techniques. We presented a convenient method for forming densely packed assembly structures of SWCNTs. The SWCNTs were treated with mixtures of HNO 3 /H 2 SO 4 or H 2 O 2 /H 2 SO 4 before and after purification, to control the packing density and porosity of the SWCNT samples. H 2 O 2 /H 2 SO 4 treatment caused a dramatic increase in microporosity without significantly changing the mesoporosity, whereas HNO 3 /H 2 SO 4 treatment decreased the mesoporosity and simultaneously increased the microporosity. This reduced mesoporosity originates from the contraction of the interbundle distance of SWCNTs. After HNO 3 /H 2 SO 4 treatment of the purified SWCNTs, the micropore surface area increased about 8.6 times compared to the pristine sample, and the volume fraction of the micropores increased from 10% to 91%, indicating formation of densely packed assemblies of SWCNTs. Therefore, HNO 3 /H 2 SO 4 treatment could control not only the SWCNT bundle size but also the interbundle distance of the SWCNTs. Moreover, the purification is of importance in promoting the formation of densely packed SWCNTs. We also demonstrated that acid treatments could develop narrow micropores, which was evidenced by CO 2 adsorption at 273 K. We emphasize that this approach can simply control the packing density as well as the porosity of SWCNT assemblies.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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