Vapor Grown Carbon Fiber Research Articles

Effect of Conductive Carbon Morphology on the Cycling Performance of Dry-Processed Cathode with High Mass Loading for Lithium-Ion Batteries

The solvent-free dry processing of electrodes is highly desirable to reduce the manufacturing cost of lithium-ion batteries (LIBs) and increase the active mass loading in the electrode. The drying process is based on the fibrillation of the polytetrafluoroethylene binder induced by shear force. This technique offers the advantage of uniformly dispersing the active material and conductive carbon without binder migration, thereby facilitating the fabrication of thick electrode with high mass loading. In this study, we explored the influence of conductive carbon morphology on the cycling performance of dry-processed LiNi0.82Co0.10Mn0.08O2 (NCM) cathodes. In contrast to Super P, which provided electronic pathways through point-contact, the fibrous structure of the vapor-grown carbon fibers (VGCFs) promoted line-contact, ensuring long and less-torturous electronic pathways and enhanced utilization of active materials. Consequently, the cathode employing fibrous VGCFs achieved higher electrical conductivity, resulting in enhanced electrochemical performance. The dry-processed NCM cathode employing VGCF with an areal capacity of 8.5 mAh cm−2 delivered a high discharge capacity of 212 mAh g−1 with good capacity retention. X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were conducted to investigate the degradation behavior of the high-mass-loaded cathodes with two different conductive carbons.

Accelerating ionic–electronic percolation pathways via catecholate coordination of bioinspired-polymer dopamine in all-solid-state composite cathode

All-solid-state batteries (ASSBs) are becoming recognized as encouraging energy storage solutions due to their great energy density and superior safety features with sulfide-based solid-state electrolytes (SSEs). However, a major challenge is the unstable interface between conductive additives and SSEs, leading to a performance degradation. To overcome this obstacle, there is an urgent need to enhance ionic conductivity at the SSE–conductive additive interface and control interfacial kinetics to prevent undesired side reactions. Herein, we investigate the critical roles of self-polymerized dopamine coated vapor-grown carbon fibers (PDA@VGCF) in optimizing ionic–electronic percolation pathways in composite cathodes. The electrochemical properties, charge transfer kinetics, and interfacial side reactions of the composite cathodes consisting of LiNi0.8Co0.15Al0.05O2–Li6PS5Cl and VGCF as a conductive additive are thoroughly examined. In practice, the composite cathode employing PDA@VGCF exhibits superior to discharge capacity of 165.5 mAh g−1 (3.81 mAh cm−2) with outstanding capacity retention (≥96 %) at a current density of 0.1C (0.46 mA cm−2) compared to the composite cathode with VGCF (118.7 mAh g−1) over 100 cycles. The enhancement can be appropriate to the integration of a PDA surface layer onto VGCF, enhancing both Li+ diffusivity and the distribution of cathode components while suppressing undesirable capacity fading. This work proposes a promising approach for the surface modification of conductive additives in composite cathodes, thereby enhancing the electrochemical performance of sulfide-based ASSBs.

Stabilization of Li[NixMnyCo1-x-y]O2 structure using a mixture of Super-P and vapor-grown carbon fiber as conducting additives

Li[NixMnyCo1-x-y]O2 (NCM) has attracted considerable attention as a cathode material because of its excellent electrochemical performance; however, practical application of NCM is challenging owing to side reactions in the electrolyte and structural changes. In this study, we manufactured NCM electrodes with mixtures of Super-P and vapor-grown carbon fiber (VGCF) as conductive additives at different ratios (Super-P/VGCF=2/8 (S2V8), 5/5 (S5V5), and 8/2 (S8V2)) and investigated the effect of the ratio of the conductive additives on NCM electrode performance. Simply changing the ratio of the conductive additives without modifying the NCM active materials substantially altered the electrochemical performance. Using a Super-P/VGCF mixture at an appropriate ratio (5/5, w/w) forms a conductive network throughout the NCM active materials, improving the electrical conductivity and enabling uniform activation across the range of NCM particles. Consequently, for S5V5, the anisotropic volume changes of the NCM primary particles became uniform, resulting in structural stability of the secondary NCM particles during charging and discharging.

A composite cathode with a three-dimensional ion/electron-conducting structure for all-solid-state lithium–sulfur batteries

All-solid-state lithium–sulfur batteries exhibit high energy densities, operate safely, and suppress polysulfide shuttling. However, their electrochemical performance is restricted by the insulating nature of sulfur and Li2S, and by severe cathode-related volumetric changes during cycling. Here, we prepare a Li2S-based cathode composite with high mixed-conductivity and stability, by infiltrating a Li2S–LiI active material solution into a mesoporous carbon replica with ~10-nm-sized pores, followed by mixing with a liquid-phase-synthesized Li6PS5Br solid electrolyte and vapour-grown carbon fibres. Benefiting from a mechanically reinforced, three-dimensional ion/electron-conducting structure, the cathode exhibits high discharge capacity (1009 mAh g−1, 20 cycles, 298 K, 0.05 C) and high reversible capacity (650 mAh g−1, 100 cycles, 298 K, 0.1 C). These findings underscore the feasibility of developing high-performance all-solid-state lithium-sulfur batteries by designing three-dimensional mixed-conducting mechanically robust cathodes.

Rational Construction of Bi2CuO12Se4 and VGCFs@Fe2O3 Composite Electrodes for High-Performance Semi-Solid-State Asymmetric Supercapacitors.

Recently, supercapacitors (SCs) are extensively explored as effective energy storage devices. Specifically, asymmetric SCs are being developed to enhance energy density using suitable materials with favorable nanostructures. This study describes the construction of a bismuth copper selenite (BCS-200) working electrode with an ultrathin nanosheet(UTNS) architecture. This morphology is achieved using a low-cost electrodeposition (ED) method, followed by annealing. The impact of ED time on the development of morphology is studied by synthesizing comparative electrodes simultaneously. The optimized BCS-200 electrode prepared with a deposition time of 200 s shows higher specific capacity/capacitance (Cs/Csc) values of 330.9 mAh g-1/2206.6 F g-1 than the other synthesized electrodes (BCS-100, BCS-150, BCS-250, and BCS-300). Besides, a vapor-grown carbon fiber (VGCF)-added Fe2O3 composite coated on nickel foam (NF) is developed as a negative electrode. The VGCFs@Fe2O3/NF electrode exhibits the (Cs/Csc) values of 183.5 mAh g-1/734.4 F g-1, which is associated with ultra-high cycling stability. In addition, the fabricated BCS-200 and VGCFs@Fe2O3/NF electrodes are combined to construct a wearable semi-solid-state asymmetric SC (SSASC) with an energy density (Ed) of 20.5Wh kg-1 and a cycling stability of 91.7% over 40000 charge/discharge cycles. Furthermore, the real-time applicability of the SSASC is verified by powering it in practical applications.

Study of the Rolling Effect on MoS2-Carbon Fiber Density and Its Consequences for the Functionality of Li-Ion Batteries.

In this study, an electrode slurry composed of molybdenum disulfide (MoS2) and vapor-grown carbon fiber (VGCF) prepared through a solid-phase synthesis method was blade-coated onto copper foil to form a thick film as the anode for lithium-ion batteries. In previously reported work, MoS2-based lithium-ion batteries have experienced gradual deformation, fracture, and pulverization of electrode materials during the charge and discharge cycling process. This leads to an unstable electrode structure and rapid decline in battery capacity. Furthermore, MoS2 nanosheets tend to aggregate over charge and discharge cycles, which diminishes the surface activity of the material and results in poor electrochemical performance. In this study, we altered the density of the MoS2-carbon fiber/Cu foil anode electrode by rolling. Three different densities of electrode sheets were obtained through varying rolling repetitions. Our study shows the best electrochemical performance was achieved at a material density of 2.2 g/cm3, maintaining a capacity of 427 mAh/g even after 80 cycles.

Concerted Effect of Ion- and Electron-Conductive Additives on the Electrochemical and Thermal Performances of the LiNi0.8Co0.1Mn0.1O2 Cathode Material Synthesized by a Taylor-Flow Reactor for Lithium-Ion Batteries.

To address the issue that a single coating agent cannot simultaneously enhance Li+-ion transport and electronic conductivity of Ni-rich cathode materials with surface modification, in the present study, we first successfully synthesized a LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material by a Taylor-flow reactor followed by surface coating with Li-BTJ and dispersion of vapor-grown carbon fibers treated with polydopamine (PDA-VGCF) filler in the composite slurry. The Li-BTJ hybrid oligomer coating can suppress side reactions and enhance ionic conductivity, and the PDA-VGCFs filler can increase electronic conductivity. As a result of the synergistic effect of the dual conducting agents, the cells based on the modified NCM811 electrodes deliver superior cycling stability and rate capability, as compared to the bare NCM811 electrode. The CR2032 coin-type cells with the NCM811@Li-BTJ + PDA-VGCF electrode retain a discharge specific capacity of ∼92.2% at 1C after 200 cycles between 2.8 and 4.3 V (vs Li/Li+), while bare NCM811 retains only 84.0%. Moreover, the NCM811@Li-BTJ + PDA-VGCF electrode-based cells reduced the total heat (Qt) by ca. 7.0% at 35 °C over the bare electrode. Remarkably, the Li-BTJ hybrid oligomer coating on the surface of the NCM811 active particles acts as an artificial cathode electrolyte interphase (ACEI) layer, mitigating irreversible surface phase transformation of the layered NCM811 cathode and facilitating Li+ ion transport. Meanwhile, the fiber-shaped PDA-VGCF filler significantly reduced microcrack propagation during cycling and promoted the electronic conductance of the NCM811-based electrode. Generally, enlightened with the current experimental findings, the concerted ion and electron conductive agents significantly enhanced the Ni-rich cathode-based cell performance, which is a promising strategy to apply to other Ni-rich cathode materials for lithium-ion batteries.

The Role of Surface Free Energy in Binder Distribution and Adhesion Strength of Aqueously Processed LiNi0.5Mn1.5O4 Cathodes

This study identifies the critical aspects of binder distribution and mechanical integrity in aqueously processed LNMO cathodes, employing a comprehensive approach involving surface characterization techniques, adhesion strength testing, and electrochemical characterization. The investigation includes the use of the Washburn and Sessile Drop methods for surface free energy analysis, revealing key insights into the interfacial free energy of adhesion between cathode constituents. The results explain the formation of carbon-binder-domains and their impact on adhesion strength, with a particular focus on the conductive additives’ (CA) surface area. The study demonstrates the effectiveness of reducing CA surface area and employing alternative conductive additives, such as vapor-grown carbon fibers (VGCF), in improving adhesion strength and mitigating capacity fade attributed to delamination during cycling. Furthermore, the research emphasizes the role of heat treatment beyond the melting point of the polyvinylidene fluoride (PVDF) latex binder, showcasing its influence on wetting and enhancing mechanical integrity. The presented methodology provides a valuable tool for predicting and optimizing binder distribution, offering insights into improving the overall performance and reliability of aqueously processed cathodes for advanced lithium-ion batteries.

TiH2-based anode: In situ formation of solid electrolyte for high volumetric energy density with minimal content of conducting agent

Herein, we report the fabrication of an electrode composite with an ultra-high active material content (90 wt%). This composite was possible because of the utilization of TiH2 as an anode active material that forms a solid electrolyte (LiH) in situ and functions as an electronic conductor, enabling a substantial reduction of the amount of conductor additive in the electrodes. The electrochemical performance of the TiH2-based electrodes with a high active material content was comparable to that of electrode composites that include a solid electrolyte because of sufficient Li+-ion conduction pathways provided by the LiH formed in situ. To further increase the capacity of the TiH2-based electrode, MgH2 (theoretical capacity: 2036 mAh/g) was mixed with TiH2 to function as an active material. TiH2, which is known to exhibit high electron conductivity and a high density, is expected to be used as a partial substitute for low-density carbon additives to increase the volumetric energy density of batteries and their active material content. Hence, the xMgH2-(1 − x)TiH2-AB (AB: acetylene black) electrode composite exhibited a high active material content (90 wt%) and improved volumetric energy density (1687 Wh/L, based on the anode) compared with a MgH2-AB (70:30 wt%) electrode composite (1157 Wh/L), even when the AB content of the xMgH2-(1 − x)TiH2-AB composite was 10 wt%. In addition, a MgH2-TiH2-VGCF (VGCF: vapor-grown carbon fiber) based electrode composite exhibited the highest volumetric and gravimetric energy density (2154 Wh/L, 1888 Wh/kg) among the investigated composites, facilitated by sufficient electron pathways provided by VGCF.

Optimizing Ionic-Electronic Pathways Via Bioinspired Self-Polymerized Dopamine in All-Solid-State Composite Cathode

The research of all-solid-state batteries (ASSBs) has been the principal emphasis in recent years. By utilizing the capabilities of advanced materials science and innovative engineering, ASSBs have the potential to revolutionize industries as diverse as consumer electronics, electric vehicles, aviation, and renewable energy. Solid-state batteries with their outstanding energy density, fast charging capabilities, and resistance to thermal runaway are anticipated to revolutionize the future of energy storage and allow a new era of eco-friendly, high-performance applications.Nonetheless, the point-of-contact resistance of ASSBs is high owing to the diverse chemical and physical characteristics of the individual solid components and the nature of solid-solid contact. To further enhance the electrochemical performance of ASSBs, especially their high-rate capabilities, it is crucial to raise the electronic conductivity of the cathode composites. Improving the electrical conductivity of electrodes to achieve high-rate capacity requires the addition of carbon. Utilizing common carbon materials, such as vapor-grown carbon fibers (VGCF), enables homogeneous current distribution in the cathode layer. Nevertheless, the use of carbon additives in sulfide-based ASSBs is inhibited by significant challenges. Carbon additives provide enough electronic percolation pathways in the composite cathodes, speeding the decomposition of sulfide SSEs during the charging process. Consequently, even with minimal amounts of carbon additives, rapid deterioration of sulfide SSEs continues to occur at the electrolyte/carbon interface, causing severe side reactions and the creation of an unfavorable interfacial layer between the carbon additives and SSEs.To achieve high cycle performance, ASSBs included conductive agents in the composite cathode to promote solid contact between the active material and sulfide solid electrolyte Li6PS5Cl; nevertheless, a significant side reaction was observed between the conductive agents and solid electrolyte. To prevent a substantial side reaction and achieve improved electrochemical performance with high-rate capacity, self-polymerized dopamine (PDA) thin film was coated on the VGCF’s surface in this investigation. Dopamine hydrochloride would be oxidized and self-polymerized into polydopamine under alkaline environments (pH 8.5) without the necessity for severe reaction conditions, sophisticated equipment, costly catalysts, or hazardous organic solvents.During the electrochemical test, the improved lithium conductivity of polydopamine-coated VGCFs after cycling at 0.1 C-rate was confirmed by galvanostatic intermittent titration technique (GITT) data and electronic-blocking cells. After polydopamine coating, the electrochemical performance of VGCFs dramatically improved with better reaction reversibility, enhanced specific capacity with high C-rate, and extended cycle life, as evidenced by polydopamine-coated VGCFs achieving ~165.5 mAh.g-1 after 100 cycles, compared to ~118.7 mAh.g-1 for unmodified VGCFs. Owing to the presence of two-electron transfer redox processes per benzoquinone skeleton, which reduced to catecholate and coordinate with lithium-ion, polydopamine facilitated a shorter ion diffusion path for a more rapid and straightforward reduction reaction even if compare with non-VGCFs composite cathode.In composite cathode, electronegative elements with lone-pair electrons, such as O (oxygen functional groups on VGCFs), react with electrophilic species, such as P5+ in Li6PS5Cl (PS4 3-), resulting in the formation of P-O bonding through nucleophilic reaction on oxygen-substituted thiophosphate and thioethers. In addition, the S atom of PS4 3- can attack the electrophilic C atom in the carbonyl group on the surface of VGCFs. Intense interactions between P5+ and the electronegative element O, as well as S2 and the electrophilic atom C, thus damage the crystal structure of SSEs and contribute to the reduction in the specific capacity of the composite cathode. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were then utilized to confirm the existence of by-products such as P-S-P, S-S, Li2S, and P-O; the presence of polydopamine demonstrated its ability to minimize side reactions and preserve the solid-state electrolyte.In addition, polydopamine's excellent adhesive capabilities enable it to build a stable and homogenous coating on the VGCF's surface. This coating may enhance the adherence of the conductive agents to the electrode's components. As polydopamine-coated VGCFs exhibited low and homogeneous resistivity in the cathode's elements, scanning spreading resistance microscopy (SSRM) was used to highlight the enhancement of particle distribution to optimize the ionic and electronic pathways.This study examines, in summary, the effect of a polydopamine coating layer on the conductivity of solid-state battery conductive agents. Even though polydopamine is recognized for its insulating characteristic, it may also display strong electrical conductivity and adhesion under certain conditions. Thus, we observed that VGCFs coated with a suitable PDA thin film eliminate unneeded kinetic energy for side reactions and improve the ionic-electronic route in composite electrodes. The discovered principles and mechanism of polydopamine coated on conductive agents are applicable to a polymer manufacturing method or modification that is coated on conductive agents, therefore enhancing the electrochemical performance of ASSBs. Figure 1

Development of Novel High Capacity Fluoride Ion Battery Cathode Utilizing Anion Redox of Sulfur

All-solid-state fluoride-ion batteries (FIBs), which are based on the shuttling of fluoride ions, have been considered as one of the promising alternates for next-generation energy storage devices because of high theoretical energy density and safety. Benefiting from the multi-covalent fluorination process, metal/metal fluorides (M/MFx) have been firstly utilized as electrode materials for FIBs with high theoretical energy densities.[1] However, M/MFx systems suffer from exceptionable volume expansion upon fluorination process due to the close-packed metal atoms, which would cause blockage of the F- diffusion pathway, resulting in devastating damage to the electrode-electrolyte interfaces. To solve these problems, cathode materials that utilize topotactic fluoride ion intercalation reactions, similar to the electrode materials applied in lithium-ion secondary batteries, are being developed.[2] Cathode materials that utilize topotactic intercalation of fluoride ions are often composed of heavier elements than the cathodes of lithium-ion batteries that use the same type of reaction mechanism, and effective anion redox is required if capacity is to be increased beyond that of lithium-ion secondary batteries.In this research, we investigated Sr2F2Fe2OS2 (SFFOS) compound with a layered structure as a novel cathode material for all-solid-state FIBs, and evaluated its electrochemical properties and elucidated the charge compensation mechanism using anion redox of sulfur.SFFOS was synthesized by a solid-state reaction under vacuum environment using SrF2, SrO, Fe, and S.[3] SFFOS/La0.9Ba0.1F2.9/vapor grown carbon fiber (VGCF) was used as the composite cathode, La0.9Ba0.1F2.9 as the electrolyte and Pb/PbF2/ La0.9Ba0.1F2.9/VGCF as the composite anode to construct the electrochemical cell. Charge-discharge measurements were carried out in the cut-off voltage range of -1.5 to 1.5 V at 140°C. Ex-situ X-ray Diffraction (XRD), X-ray absorption spectroscopy (XAS) measurements of Fe K-edge, S K-edge, O K-edge and F K-edge were carried out under different state of charge during the 1st and the 2nd cycle.SFFOS showed reversible intercalation/de-intercalation of fluoride ions and a capacity of ~6.1 fluoride ions per unit cell (403 mAh g-1). The charge compensation mechanism was revealed for SFFOS by XAS measurements, where S redox contributed to the whole voltage range from -1.5 V to 1.5 V vs. Pb/PbF2, and Fe+2/+3 redox contributed from the middle SOC. The S-S dimers were formed upon charging, which was similar to the trapped O2 molecules observed in lithium-excess metal oxide during charge process[4]. Not only can the F- anions insert around Fe to form Fe-F bonds, but the excess F- anions can also occupy the Sr-S interstitial layers in the original lattice. Compared to the Fe-based layered oxide Sr3Fe2O5, the Fe-based oxysulfide SFFOS showed a lower average voltage but a higher specific capacity. We believe that this study could provide a new understanding of sulfur-based charge compensation and electrochemical fluorination reactions. Reference s : [1] D. Zhang, K. Yamamoto, Y. Uchimoto et al., J. Mater. Chem. A, 2021, 9, 406–412.[2] Y. Wang, K. Yamamoto, Y. Uchimoto, et al., Chem. Mater., 2022, 34, 609–616.[3] Kabbour H, Janod E, Corraze B, et al ., J. Am. Chem. Soc., 2008, 130(26): 8261-8270.[4] R. A. House, P. G. Bruce, et al., Nat. Energy 2020, 5, 777–785. Figure 1

Intercalation Reaction Mechanism of Fluoride-Ions in (Ca, Sr)FeO2 Cathodes with Infinite Layer Structure for All-Solid-State Fluoride-Ion Batteries

Fluoride ion batteries, which use fluoride ions as carriers, are attracting attention as the next generation of storage batteries because of their theoretical high energy density. Conventional research has focused on metal/metal fluorides such as Cu/CuF2 as cathode materials.[1] However, these cathodes have disadvantages of the power density and cyclability due to the rapid decrease in electronic conductivity and large volume change during fluorination and defluorination. To solve these problems, cathode materials that utilize topotactic fluoride ion intercalation reactions, similar to electrode materials applied in lithium-ion secondary batteries, are being developed[2]. However, these materials have the disadvantage of relatively small capacity, compared to metal/metal fluorides.In this study, we focused on SrFeO2and Ca-doped SrFeO2 cathodes with infinite layer structure as new high-capacity intercalation cathodes, and evaluated its electrochemical properties and clarified the charge compensation mechanism.Ca1-xSrxFeO2 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) was synthesized by a low-temperature reduction method using CaH2. Ca1-xSrxFeO2/La0.9Ba0.1F2.9/vapor grown carbon fiber (VGCF) was used as the composite cathode, La0.9Ba0.1F2.9 as the electrolyte and Pb/PbF2/ La0.9Ba0.1F2.9/VGCF as the composite anode to construct the electrochemical cell of the piezoelectric material. Charge-discharge measurements were carried out in the cut-off voltage range of -1.5 to 3.0 V at 140°C. X-ray absorption spectroscopy (XAS) measurements of Fe K-edge, O K-edge, and F K-edge and resonant inelastic X-ray scattering (RIXS) measurements of O K-edge were performed on the samples after charging and discharging.All the Ca1-xSrxFeO2 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) cathode showed voltage plateaus around -0.5 V and 1.5 V during charging, and the maximum discharge capacity (580 mAh g-1) was obtained when x = 0.8, and the cathodes could be repeatedly charged and discharged. XAS of the Fe K-edge revealed that Fe compensated for the charge in the flat potential region around -0.5 V. XAS and RIXS measurements of the O K-edge revealed that the charge compensation was carried out by the formation of O2 molecules (oxidation of oxide ions), as which is observed in lithium-excess metal oxide on charge process[4], in the voltage plateau around 1.5 V. Using inexpensive Ca and Fe, we succeeded in developing an intercalation cathode material that significantly exceeds the capacity of conventional lithium-ion battery cathodes.

Comparison of micro- and macro-tribological properties of carbon composites reinforced by vapor-grown carbon fibers

Carbon composites were prepared from furan resins filled with vapor-grown carbon fibers (VGCFs). The resistances and densities of the composites, affected by the adhesion between the matrix and VGCFs, remained almost constant with VGCF concentration. The micro- and macro-friction coefficients of the composites were measured using a friction force microscope and pin-on-drum tribology apparatus, respectively. With increasing VGCF concentration, the micro-friction coefficients of the matrix increased, thereby reflecting an increase in roughnesses. In contrast, the micro-friction coefficients of the interfaces between the matrix and VGCF, with changes strongly correlated with the macro-friction coefficients of the composites, remained almost constant.

Difference in carcinogenicities of two different vapor grown carbon fibers with different physicochemical characteristics induced by intratracheal instillation in rats

BackgroundCarbon fibers are high aspect ratio structures with diameters on the submicron scale. Vapor grown carbon fibers are contained within multi-walled carbon tubes, with VGCF™-H commonly applied as a conductive additive in lithium-ion batteries. However, several multi-walled carbon fibers, including MWNT-7, have been reported to induce lung carcinogenicity in rats. This study investigated the carcinogenic potential of VGCF™-H fibers in F344 rats of both sexes with the vapor grown carbon fibers VGCF™-H and MWNT-7 over 2 years. The carbon fibers were administered to rats by intratracheal instillation at doses of 0, 0.016, 0.08, and 0.4 mg/kg (total doses of 0, 0.128, 0.64, and 3.2 mg/kg) once per week for eight weeks and the rats were observed for up to 2 years after the first instillation.ResultsHistopathological examination showed the induction of malignant mesothelioma on the pleural cavity with dose-dependent increases observed at 0, 0.128, 0.64, and 3.2 mg/kg in rats of both sexes that were exposed to MWNT-7. On the other hand, only two cases of pleural malignant mesothelioma were observed in the VGCF™-H groups; both rats that received 3.2 mg/kg in male. The animals in the MWNT-7 groups either died or became moribund earlier than those in the VGCF™-H groups, which is thought related to the development of malignant mesothelioma. The survival rates were higher in the VGCF™-H group, and more carbon fibers were observed in the pleural lavage fluid (PLF) of the MWNT-7 groups. These results suggest that malignant mesothelioma is related to the transfer of carbon fibers into the pleural cavity.ConclusionsThe intratracheal instillation of MWNT-7 clearly led to carcinogenicity in both male and female rats at all doses. The equivocal evidence for carcinogenic potential that was observed in male rats exposed to VGCF™-H was not seen in the females. The differences in the carcinogenicities of the two types of carbon fibers are thought due to differences in the number of carbon fibers reaching the pleural cavity. The results indicate that the carcinogenic activity of VGCF™-H is lower than that of MWNT-7.

Broadband and strong microwave absorption combining excellent EMI shielding of VGCF/carbonyl iron composites derived from synergistic magnetic and dielectric losses

As one of the most effective approaches to reduce microwave radiation in electromagnetic stealth and compatibility, broadband microwave absorbers have attracted widespread attention. However, it is challenging to maintain broadband absorption performance and maintain thin thickness simultaneously. Herein, by cooperating electromagnetic characteristics of vapor-grown carbon fiber (VGCF) and flaky carbonyl iron particles (CIP) to manipulate complex permittivity and complex permeability, a broadband metastructure absorber is proposed. The local conducting network composed of VGCF enriches the transmission path and greatly boosts dielectric loss capability of VGCF/CIP composites. The constructed VGCF/CIP reinforced metastructure absorber covered the 95% (−13 dB) absorption bandwidth in the full frequency band of 2–18 GHz at 8.4 mm thickness. The outstanding microwave absorption performance is benefit from the synergistic effect of magnetic-dielectric characteristics of the VGCF/CIP composite. The result provides a multi-resonant coupling mode to improve the overall impedance matching characteristics, which opens up a broad prospect for the development of ultra-wideband microwave absorbing materials. Moreover, VGCF/CIP composite shows a high electromagnetic interference (EMI) shielding effectiveness, and the excellent green shielding index (gs) of more than 10 indicates its potential application as an EMI shielding material.

Rationally Designed Solution-Processible Conductive Carbon Additive Coating for Sulfide-based All-Solid-State Batteries.

Sulfide-based all-solid-state batteries (ASSBs) have emerged as promising candidates for next-generation energy storage systems owing to their superior safety and energy density. A conductive agent is necessarily added in the cathode composite of ASSBs to facilitate electron transport therein, but it causes the decomposition of the solid electrolyte and ultimately the shortening of lifetime. To resolve this dilemmatic situation, herein, we report a rationally designed solution-processible coating of zinc oxide (ZnO) onto vapor-grown carbon fiber as a conductive agent to reduce the contact between the carbon additive and the solid electrolyte and still maintain electron pathways to the active material. ASSBs with the carbon additive with an optimal coating of ZnO have markedly improved cycling performance and rate capability compared to those with the bare conductive agent, which can be attributed to hindering the decomposition of the solid electrolytes. The results highlight the usefulness of controlling the interparticle contacts in the composite cathodes in addressing the challenging interfacial degradation of sulfide-based ASSBs and improving their key electrochemical properties.

In-situ CNT-loaded organic cathodes for sulfide all-solid-state Li metal batteries

Organic cathodes show promising advantages of extensive resources, high theoretical specific capacity, and mild synthesis conditions, etc., but suffer from low density, poor electronic conductivity, and high solubility in liquid electrolytes. Herein, an in-situ coating method is developed to overcome the above issues by realizing high-performance sulfide all-solid-state batteries with organic Li4C8H2O6 cathode. Li4C8H2O6 composite cathodes with carbon nanotubes (CNTs) and vapor grown carbon fiber (VGCF) were systematically studied to reveal that CNTs accelerate the electrochemical decomposition of sulfide electrolyte, despite the effectively improved electronic conductivity, rate capability and active material utilization. Therefore, in-situ coating of Li4C8H2O6 onto CNTs (Li4C8H2O6@CNT) is developed to further improve the contact between Li4C8H2O6 and CNTs, but to reduce the contact of CNTs with sulfide solid electrolyte and its decomposition. As a result, the Li4C8H2O6@CNT electrode demonstrates a high capacity of 200.3 mAh/g, and a high active material utilization rate (83.4% at 0.1C). It also exhibits a specific capacity of 85.9 mAh/g at a high cathode loading of 40 wt% and a high rate of 1C.

Synthesis and Performance of NaTi2(PO4)3/VGCF@C Anode Composite Material for Aqueous Sodium-Ion Batteries

This study combines self-prepared NaTi2(PO4)3 (NTP) with commercial vapor-grown carbon fiber (VGCF) using a solid state calcination, then coats it with carbon to synthesize the composite anode material NaTi2(PO4)3/VGCF@C (NTP/VGCF@C). The microstructure and electrochemical properties of the composite material were then analyzed using microstructure analysis and electrochemical testing equipment. Single phase NTP shows nanoparticles with a polyhedral structure, and there is good contact at the interface between the nanoparticles and the VGCFs. The carbon coating formed on the NTP particles displays a nearly 6.5 nm thick layer of amorphous carbon. From the coin-cell battery performance measurements, after 850 cycles, the composite material NTP/VGCF@C exhibits an excellent retention rate of 96.3% compared to that of the pure NTP material when the current density is 200 mA/g. As a result, the composite material and lithium manganate (denoted as LMO) were assembled into an LMO-NTP/VGCF@C aqueous sodium-ion soft pack full battery system. The full battery shows an initial capacity of 31.07 mAh at a rate of 0.5C, and a reversible discharge capacity retention rate of 95.8% after 480 cycles, exhibiting a good long-cycle stability performance.

Elastic Electrically Conductive Composites Based on Vapor-Grown Carbon Fibers for Use in Sensors.

Elastic electrically conductive composites with an ethylene octene copolymer matrix (EOC) and vapor-grown carbon fibers (VGCF) were prepared by ultrasonication in a toluene solution, and their morphology, mechanical and electrical properties were also evaluated. EOC/CF composites were estimated for their mechanical and viscoelastic properties. The morphology of the composites was analyzed using scanning electron microscopy (SEM), and stress-strain curves were generated to measure the stress and tensile modulus of the composites. The experimental results were compared with various theoretical models, including the Burgers model, which separates viscoelastic behavior into several components. A dynamic mechanical analysis was also used to measure the composites' storage modulus, loss modulus, and damping factor at different frequencies. The composites' complex viscosity and storage modulus were increased with higher wt.% of CF, which enhances the elastic response. Electrical resistivity measurements were conducted on the composites and it was found that the resistivity decreased as the sample was loaded and increased as it was unloaded. Overall, the study provides insights into the mechanical and viscoelastic properties of EOC/CF composites, which could be helpful in developing sensors such as pressure/strain sensors.

Thermal Properties of Carbon Nanofiber Sheet for Thermal Interface Materials under High Temperature and Humidity

In this study, polyvinyl alcohol (PVA) - polytetrafluoroethylene (PTFE) - vapor grown carbon fiber (VGCF) sheets are fabricated as a new paper-like thermal interface material (TIM), which is a potential substitute for traditional TIMs. Two types of PVA-PTFE-VGCF sheets were fabricated by using 120 nm and 300 nm PTFE particles. The microstructure shows that the VGCFs were arranged in random directions inside the sheet and interconnected via the aggregate of PVA. 300 nm PTFE particles were well distributed within the sheet, while 120 nm PTFE particles aggregated partially and formed pores nearby. The fabricated sheets have a low thickness of 31.2 um and 28.2 um, and lightweight properties with a density of 0.79 × 106 g·m−3 and 0.91 × 106 g·m−3, respectively. With the addition of 300 nm PTFE particles, the fabricated sheet has higher thermal conductivities of 9.81 W·m−1·k−1 in the in-plane direction and 2.11 W·m−1·k−1 in the through-plane direction. In the high temperature and humidity test, the thermal conductivities of the fabricated sheet were increased due to the rearrangement of PVA and PTFE particles.