Simple fabrication of a Fe2O3/carbon composite for use in a high-performance lithium ion battery

A simple approach was developed for the fabrication of a Fe₂O₃/carbon composite by impregnating activated carbon with a ferric nitrate solution and calcinating it. The composite contains graphitic layers and 10 wt.% Fe₂O₃ particles of 20–50 nm in diameter. The composite has a high specific surface area of ∼828 m² g⁻¹ and when used as the anode in a lithium ion battery (LIB), it showed a reversible capacity of 623 mAh g⁻¹ for the first 100 cycles at 50 mA g⁻¹. A discharge capacity higher than 450 mAh g⁻¹ at 1000 mA g⁻¹ was recorded in rate performance testing. This highly improved reversible capacity and rate performance is attributed to the combination of (i) the formation of graphitic layers in the composite, which possibly improves the matrix electrical conductivity, (ii) the interconnected porous channels whose diameters ranges from the macro- to meso- pore, which increases lithium-ion mobility, and (iii) the Fe₂O₃ nanoparticles that facilitate the transport of electrons and shorten the distance for Li⁺ diffusion. This study provides a cost-effective, highly efficient means to fabricate materials which combine conducting carbon with nanoparticles of metal or metal oxide for the development of a high-performance LIB.     

SiN/bamboo like carbon nanotube composite electrodes for lithium ion rechargeable batteries

A dual stage technique employing hot filament chemical vapor deposition (HFCVD) and radio frequency sputtering was used to synthesize SiN/BCNTs (bamboo like carbon nanotubes) on copper substrates. The films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Electron field emission studies (EFE), charge-discharge, and cyclic voltammetry. The comprehensive characterization is consistent with a nanolayer of amorphous SiN on BCNTs. Field emission experiments confirm the excellent contact of the SiN nanolayer with the surface of the BCNTs necessary for fabrication of a coin cell. Electrochemical testing shows that SiN/BCNT electrode can deliver an initial discharge capacity of 2000 mAh g⁻¹ which is higher than the capacity of graphite and the reversible capacity after ten cycles is 300 mAh g⁻¹. The cyclic voltammetry results suggest good reversibility with Li during cycling.     

Simple approach for the fabrication of carbon nanotube field emitter using conducting paste

A conducting layer using carbon nanotube (CNT) paste was prepared by mixing multi-walled CNT (MWNT), organic vehicles and spin on glass (SOG). The effect of SOG on the properties of the CNT paste was evaluated and compared to that of CNT paste with a glass frit. CNT powders were coated on the conducting CNT film either by sprinkling CNT powders onto the overall conducting layer area or by dropping a solution containing well dispersed CNTs. CNTs were strongly fixed by the formation of silica after heat treatment. The samples showed good field emission characteristics with turn-on electric fields of approximately 1.6 ∼ 2.2 V/μm. SOG was found to be an efficient inorganic binder for CNTs in the CNT paste.     

In-situ fabrication of heterostructured SnOx@C/rGO composite with durable cycling life for improved lithium storage

Due to their ultra-high theoretical capacity and low discharge potential, rich Sn-based materials are considered promising candidates for lithium ion battery (LIB) anodes; however, the development of SnO_x electrodes is restricted by their low conductivity and severe volume change during repeated cycling. In this study, carbon matrix encapsulating heterostructured SnO_x ultrafine nanoparticles (SnO_x@C/rGO) were synthesized in situ through a facile solvent mixing, followed by thermal calcination. During the decomposition of the Sn-organic precursor, the sizes of the as-prepared SnO_x nanoparticles were strictly controlled to 5–10 nm; they were intimately wrapped by the in-situ formation of ultrathin carbon layers, which prevented the agglomeration of nanograins. Furthermore, the SnO_x@C nanoparticles were evenly anchored on the surface of reduced graphene oxide (rGO) to construct a highly conductive carbon framework. It is notable that the carbon matrix prepared in situ can accommodate the volumetric change of SnO_x and facilitate the transport of Li⁺ ions during continuous cycling. Benefiting from the synergistic effect between the SnO_x nanoparticles and carbon matrix prepared in situ, the heterostructured SnO_x@C/rGO will confer improved structural stability and reaction kinetics for lithium storage. It delivers a stable reversible discharge capacity of 1092.2 mAh g⁻¹ at a current rate of 0.1 A g⁻¹, and enhanced cycling retention with a capacity of 447.8 mAh g⁻¹ after 1200 cycles at a current rate of 5.0 A g⁻¹. This strategy provides a rational avenue to design oxide anodes with efficient hierarchical structure for LIB development.     

Facile fabrication of polystyrene/carbon nanotube composite nanospheres with core-shell structure via self-assembly

In this paper, a novel method for fabrication of core-shell nanospheres with polystyrene (PS) as the core and multi-walled carbon nanotubes (MWNTs) as the shell via hydrogen-bonding self-assembly is introduced. The PS nanospheres with carboxyl acid groups on the surface (PS-COOH nanospheres) were prepared by typical soap-free emulsion copolymerization with acrylic acid as comonomer. The MWNTs were grafted with poly(vinyl pyrrolidone) (PVP), in which the carbonyl oxygen can act as proton acceptors to form hydrogen bonds with the carboxyl acid groups. The results show that the functionalized MWNTs can self-assemble onto the surface of PS-COOH nanospheres rapidly via hydrogen bonding interaction, and the process is reversible and can be well controlled by adjusting pH value of the system. These core-shell nanospheres have the potential to be used as conductive and synergistic reinforcement fillers in fabricating high-performance and functional nanocomposites.     

Fabrication and characterization of magnetic cobalt ferrite/polyacrylonitrile and cobalt ferrite/carbon nanofibers by electrospinning

An electrospinning process was used to fabricate cobalt ferrite (CoFe₂O₄)-embedded polyacrylonitrile (PAN) nanofibers. Oleic acid-modified CoFe₂O₄ nanoparticles were dispersed in the PAN before spinning. The surface morphologies and structures of the nanofibers were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM observation showed that the average diameter of the CoFe₂O₄/PAN nanofibers was 110 nm, and the magnetic CoFe₂O₄ nanoparticles were embedded in the PAN nanofibers. X-ray photoelectron spectroscopy was used to characterize the CoFe₂O₄/PAN and CoFe₂O₄/carbon nanofibers. Fiber magnetic properties were measured by vibrating sample magnetometry, showing that the saturation magnetization of the CoFe₂O₄/PAN nanofibers was 45 emu/g and that the fibers demonstrated superparamagnetic behavior.     

功能化碳纳米管/聚合物复合分离膜

碳纳米管不仅具有优异的力学性质和超大的比表面积,同时具有优良的传输特性,将其添加到聚合物中制备复合分离膜,具有广阔的应用前景。通过化学改性将碳纳米管功能化,提高其在聚合物中的分散性,制备碳纳米管/聚合物复合膜。本文在介绍了碳纳米管功能化、碳纳米管/聚合物复合膜制备方法的基础上,综述了功能化碳纳米管的加入对复合分离膜亲水性、水通量、机械稳定性以及分离等性能的影响。总结了近年来对碳纳米管在聚合物膜内定向排列的研究进展及碳纳米管定向对复合膜相关性能的影响。由于碳纳米管材料的各向异性,利用电场、磁场及流场等对碳纳米管在聚合物膜内的分布进行定向,从而充分利用其优异的性能,是该类复合膜的研究方向。     

活性炭/碳纳米管复合电极电吸附机理研究

按活性炭∶碳纳米管∶PVDF=7.2∶0.8∶2质量比制备活性炭/碳纳米管复合电极,并对其构成的EST模块进行吸附动力学、等温吸附和电迁移拟合研究,分析其吸附机理。结果表明,准一级反应动力学模型和Langmuir模型能够很好的拟合、描述活性炭/碳纳米管复合电极在EST脱盐过程中的吸附机理,说明电吸附速率只与一种反应物的浓度有关且是单离子层吸附,EST吸附过程中离子的电迁移率随迁移时间的变化趋势可以用指数形式的方程很好的拟合。     

The impact of microwave-assisted sintering on fabrication of cobalt ferrite nanostructure foams for gas-sensing

This study employed the Pechini-type sol-gel method to synthesize single-phase cobalt ferrite nanoparticles with almost spherical morphology and an average size of ～50 nm. The Pechini sol-gel is based on the polysterification reaction between citric acid and ethylene glycol and the formation of colloidal nanoparticles due to the polymerization of an iron-cobalt complex. Foam samples were prepared from the obtained nanoparticles by using urea as the progenic agent and subsequent conventional or microwave sintering. The average grain size values for the microwave and conventionally sintered foam samples were 90 and 280 nm, respectively. Microwave sintering has successfully hindered grain growth regarding the initial ～50 nm size of the cobalt ferrite nanoparticles. The microwave sintered foam sample showed an approximately two-fold increase in the surface area value compared to its conventionally sintered counterpart. The pore volume for the conventionally and microwave sintered samples was measured at 0.007 and 0.026 cc/g, respectively. Also, the pore diameter values were measured to be less than 2.5 nm in both samples. The pore size distribution within the microwave sintered sample was unimodal, while the conventionally sintered sample showed a bimodal one. The gas-sensing properties of the samples were examined in pure ethanol, acetone, and liquefied petroleum gas (LPG) atmospheres at different temperatures. The results indicated that for all the samples and in all the three atmospheres, the best working temperature is 300 °C. The microwave sintered foam sample showed the highest sensitivity and the shortest response time. This sample was more selective towards ethanol than the other two gases.     

Defect engineering on the defluorinated MWCNTs@SnO2@N-doped carbon composite for enhanced lithium storage performance

When tin oxide (SnO₂) is used in the anode of lithium-ion batteries, its capacity decreases dramatically due to poor conductivity and volume effects during the electrochemical cycle. Although composites with traditional carbon-based materials can improve this shortcoming, the low capacitance of such materials still limits the capacity of the composites. Therefore, we applied defect engineering to SnO₂/C composite electrodes for the first time, and prepared D-MWCNTs@SnO₂@N–C composite electrodes with hollow rod structures. Defects were constructed in the carbon materials to promote electron diffusion and ion storage active sites. The hollow structure can adapt to the volume change that occurs during Li-ion insertion/desorption. In addition, the detachment of F atoms and the insertion of N atoms, which are chemical processes that occur on the surface of carbon materials, promote an increase in surface porosity and defect density, thereby providing additional lithium storage sites. The double carbon effect caused by defect engineering provides a multidimensional transport path and rapid migration rate for Li-ions, which enables the electrode to display excellent electrochemical performance; thus, this work could lead to the preparation of next-generation anode materials with high energy storage capacity, high rate capability and high cycle stability.     

Thick vertically aligned carbon nanotube/carbon composite electrodes for electrical double-layer capacitors

We present a new method for synthesis of thick, self-standing porous carbon electrodes with improved physicochemical properties and unique porous structure. The synthesis is based on the use of vertically aligned carbon nanotubes (VACNT) as templates for polymer-based activated carbon materials. The VACNT template enables the production of 1 mm thick, binder-free electrodes with high capacity values even at high rates (>160 Fg⁻¹ at more than 1 Ag⁻¹ for 1 mm thick electrode), and very good stability upon cycling. The electrochemical performance after more than 50,000 cycles, the pore characterization by adsorption isotherms, and the structural analysis of the composite electrode are also reported.     

改性活性炭/碳纳米管复合电极脱盐性能研究

采用改性CNT*作为CDI电极导电剂,制备AC*/CNT*复合电极,考察其脱盐性能。利用BET、FTIR和TEM对AC或CNT的表面结构、官能团种类和分散性进行分析。利用电化学工作站和SEM对复合电极的比电容、阻抗和表面形貌进行分析。结果表明,通过改性,AC*的比表面积达到672.48 m2/g,增加了29.43%;CNT*的比表面积为117.39 m2/g,下降了9.94%,但其分散性得到有效改善。根据循环伏安测试和静态脱盐实验结果 ,按AC*∶CNT*∶PVDF=7.2∶0.8∶2质量比制备的电极效果最好,比电容高达130.48 F/g,比吸附量达到7.29 mg/g。     

半纤维素/碳纳米管复合凝胶的溶胀性能

采用 (NH4)2S2O8-Na2SO3为引发剂体系,N,N-亚甲基双丙烯酰胺（BIS）为交联剂,利用自由基聚合法成功制备了半纤维素/碳纳米管复合凝胶。用SEM对凝胶的结构形态进行了研究分析;研究了单体比例、碳纳米管含量和pH值对凝胶溶胀率的影响;并应用溶胀动力学方程对试验数据进行拟合。研究结果表明：半纤维素/碳纳米管复合凝胶的溶胀率随着甲基丙烯酸/半纤维素比例的增加而减小,随着碳纳米管含量的增加而减小;pH≤11时随pH值的增加而增大,pH>11时随pH值的增加而减小。拟合结果表明整个溶胀过程符合Schott二级动力学模型。     

Hard carbon/lithium composite anode materials for Li-ion batteries

Hard carbon/lithium composite anode electrode is prepared to reduce the initial irreversible capacity of hard carbon, which hinders practical application of hard carbon in lithium ion batteries, by introducing lithium into hard carbon. Lithium foil effectively compensates the irreversible capacity of hard carbon in the first cycle. A full cell using LiCoO₂ cathode and the composite anode shows much higher initial coulombic efficiency than that of a cell using LiCoO₂ cathode and hard carbon anode. This paves the way to reduce the large initial irreversible capacity of hard carbon. Besides that, this composite anode enables conductive polymer/sulfur composite cathode to be used in Li-ion batteries with non-lithiated anode materials.     

Enhanced lithium storage in a VO2(B)-multiwall carbon nanotube microsheet composite prepared via an in situ hydrothermal process

A novel VO₂(B)-multiwall carbon nanotube (MWCNT) composite with a sheet-like morphology was synthesized by a simple in situ hydrothermal process. The morphology and structural properties of the samples were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). FE-SEM observations demonstrated that the nanosheets are frequently grown together in the form of bundles composed of numerous nanosheets, each with a smooth surface and a typical length of 300-500 nm, width of 50-150 nm, and thickness of 10-50 nm. Electrochemical measurements were carried out using different discharge cut-off voltages. Electrochemical tests show that the VO₂(B)-MWCNT composite cathode features long-term cycling stability and high discharge capacity (177 mAh g⁻¹) in the voltage range of 2.0-3.25 V at 1 C with a capacity retention of 92% after 100 cycles. The electrochemical impedance spectra (EIS) indicate that the VO₂(B)-MWCNT composite electrode has very low charge-transfer resistance compared with pure VO₂(B), indicating the enhanced ionic conductivity of the VO₂(B)-MWCNT composite. The enhanced cycling stability is attributed to the fact that the VO₂(B)-MWCNT composite can prevent the aggregation of active materials, accommodate the large volume variation, and maintain good electronic contact. We strongly believe that the VO₂(B)-MWCNT composite can be considered as a potential cathode material for lithium-ion batteries.     

Synthesis and mechanical properties of carbon nanotube/diamond-like carbon composite films

Diamond-like carbon (DLC) coatings were successfully deposited on carbon nanotube (CNT) films with CNT densities of 1 × 10⁹/cm², 3 × 10⁹/cm², and 7 × 10⁹/cm² by a radio frequency plasma-enhanced chemical vapor deposition (CVD). The new composite films consisting of CNT/DLC were synthesized to improve the mechanical properties of DLC coatings especially for toughness. To compare those of the CNT/DLC composite films, the deposition of a DLC coating on a silicon oxide substrate was also carried out. A dynamic ultra micro hardness tester and a ball-on-disk type friction tester were used to investigate the mechanical properties of the CNT/DLC composite films. A scanning electron microscopic (SEM) image of the indentation region of the CNT/DLC composite film showed a triangle shape of the indenter, however, chippings of the DLC coating were observed in the indentation region. This result suggests the improvement of the toughness of the CNT/DLC composite films. The elastic modulus and dynamic hardness of the CNT/DLC composite films decreased linearly with the increase of their CNT density. Friction coefficients of all the CNT/DLC composite films were close to that of the DLC coating.     

Mechanical properties of carbon nanotube/carbon fiber reinforced thermoplastic polymer composite

Carbon nanotube (CNT)/carbon fiber (CF) hybrid fiber was fabricated by sizing unsized CF tow with a sizing agent containing CNT. The hybrid fiber was used to reinforce a thermoplastic polymer to prepare multiscale composite. The mechanical properties of the multiscale composite were characterized. Compared with the base composite (traditional commercial CF), the multiscale composite reinforced by the CNT/CF hybrid fiber shows increases in interlaminar shear strength (ILSS) and impact toughness. Laminate containing CNTs showed a 115.4% increase in ILSS and 27.0% increase in impact toughness. The reinforcing mechanism was also discussed by observing the impact fracture morphology. POLYM. COMPOS., 38:2001–2008, 2017. © 2015 Society of Plastics Engineers     

A novel germanium/carbon nanotubes nanocomposite for lithium storage material

A new nanocomposite of Ge/carbon nanotubes (n-Ge/CNTs) was reported by a facile precursor method through a pyrolysis technique. Among it, germanium nanoparticles are encapsulated with a thin layer of amorphous carbon, which benefits to keep a good electronic contact with carbon nanotubes. Germanium nanoparticles are mainly supported inside the carbon nanotubes, which can effectively buffer the volume changes of Germanium. The composite was an effectively mixed (Li⁺ and e⁻) conducting network, which is vital to a quick Li insertion. The composite was shown to exhibit a reversible capacity of about 750 mAh g⁻¹ (74.4 mA g⁻¹) and an improved rate performance, compared with that of CNTs processed as the same condition. Our results demonstrated the composite to be a good active Li-storage material for Li batteries.     

碳纳米管/聚丙烯腈复合纤维的制备及结构研究

通过原位聚合的方法制备了碳纳米管/聚丙烯腈(CNTs/PAN)聚合液,用湿法纺丝工艺制备了CNTs/PAN复合纤维,分析了复合纤维流变性能、热性能及截面形貌。结果表明:CNTs的加入使得聚合物溶液出现了假凝胶化,粘度和弹性均有所上升,纺丝时溶液细流的表层遇水迅速凝固成致密的皮层,影响了纤维芯部的二甲基亚砜(DMSO)和水的双扩散作用,凝固丝出现了很明显的皮芯结构,CNTs的加入还使得纤维预氧化放热过程得到了缓和。     

石蜡/碳纳米管复合相变材料的性能研究

针对太阳能烟囱蓄热单元的应用需求,以石蜡为相变材料,向其中添加碳纳米管,通过两步法制备出碳纳米管质量分数分别为0.5%、1%、2%、3%、5%的复合相变材料,并对其热物性及循环稳定性进行了实验研究。结果显示,碳纳米管的添加可以有效提高相变材料的热导率和相变过程的传热速率,当添加的质量分数为5%时,其热导率达0.62 W/m2·K,比纯石蜡提高了1.21倍,蓄、放热速率分别比纯石蜡提高了44%、45%;碳纳米管的添加降低了相变材料的相变潜热,当添加的质量分数为5%时,其相变潜热为170 J/g,为纯石蜡的81%;石蜡与碳纳米管只是简单的物理复合,且制备的相变复合材料具有较好的循环稳定性。