Electrical Conductive Network Research Articles

Advanced Lithium-Sulfur Batteries with Carbon Nanotubes As Conductive Networks

Lithium-sulfur batteries, with the high theoretical capacity (1675 mAh g-1) and energy density (2600 Wh kg-1) as well as the easy access and non-toxic of raw materials, demonstrate a promising prospect among the high energy storage systems for electric vehicles (EVs) and portable electronic devices. However, there are also several issues to be handled before commercial application.Firstly, different from traditional lithium-ion batteries, intermediate polysulfides generate and dissolve in the organic electrolyte during the discharge process of lithium-sulfur batteries. The dissolved polysulfides, shuttle between cathode and anode sides, lowering the utilization of sulfur and also react with the lithium anode without any electron transfer. However, the dissolution of polysulfide in a lithium-sulfur battery is highly dependent on the sulfur/electrolyte loading. Thus an appropriate dosage of electrolyte will build a concentration gradient, which will limit the dissolution of polysfulfides. In our work, A lithium-sulfur cell with a high initial discharge capacity of 1053 mAh g-1 at a high rate of 1 C and an ultralow decay rate of 0.049 %/per cycle during 1000 cycles was obtained by using CNT-sulfur cathode and suppressing polysulfide shuttle to a shuttle factor of 0.02 by matching the sulfur/electrolyte loading. Secondly, sulfur is with low electrical conductivity (5×10-30 S cm-1 at 25 oC) and extra conductive network is highly required. Generally, the addition of conductive materials will neutralize the advantage in high energy density of lithium-sulfur battery. Thus, the more sulfur content in the composite cathode, the larger energy density. Herein, we employed the carbon nanotubes (CNTs) to build the unblocked conductive skeleton and a room-temperature, one-step ball-milling treatment of aligned CNTs and sulfur was applied to obtain high sulfur content of 90 %. The 90 % sulfur loading cathode exhibited a superior density of 1.98 g cm-3 (2.07 g cm-3for sulfur), which will greatly increase the volumetric energy density of lithium-sulfur battery. Reference: [1] XB Cheng, et al. J. Power Sources, 2014, DOI: 10.1016/j.jpowsour.2013.12.031[2] XB Cheng, et al. Nano Energy, 2014, accepted

Electrochemical performance of LiFePO4@C composites with biomorphic porous carbon loading and nano-core–shell structure

Effect of biomorphic porous carbon (BPC) addition on the composition, microstructure, and electrochemical performance of LiFePO4@C/C composites was investigated. Results indicated that network pores of BPC were almost completely filled by LiFePO4@C nanoparticles, which were formed by an olivine structure LiFePO4 core with size that ranged from 58.6nm to 80.1nm and an amorphous carbon shell with a thickness of approximately 2nm. Double electrical conductive networks formed in the composites improved the electrical properties of samples from 2.59×10−6Scm−1 (sample A-0) to 5.76×10−2Scm−1 (sample A-20). Synergy effect of electric double layer energy storage produced by BPC and lithium-ion extraction/insertion energy storage by LiFePO4 clearly reduced the capacity reduction rate of composites, and obtained a charge/discharge capacity of 114.2/110.5mAhg−1 (sample A-5) at 10C. Moreover, addition of BPC showed a significant advantage in reducing the interfacial resistance of the electrode reaction in composites from 86.72Ω (sample A-0) to 37.58Ω (sample A-20). The electrical conductive mechanism of LiFePO4@C/C composites is discussed.

A Nanoarchitectured Porous Electrode Assembly of NiSi Thin Film for Lithium Ion Batteries

This study proposes to produce well-aligned nanorod arrays containing NiSi thin film to improve the electrochemical performance of Si based anodes. In this respect, NiSi thin films made of nanorods are produced via glancing angle electron beam deposition (GLAD) technique. The structural and morphological properties are investigated using thin film X-ray diffraction (XRD) and scanning electron microscopy (SEM). The well aligned nanorod arrays containing NiSi thin film anode exhibits a long cycle life with a moderate capacity retention (around 1100mAhg-1 for 100 cycles). This remarkable electrochemical performance can be explained by the electrode composition, structure and morphology: During Li+ insertion into the alloyed thin film electrodes, Si acts as active center, which reacts with Li+ to form amorphous LixSi alloys, while the nanosized Ni particles are believed to provide electrical conduction network inside the active material and buffer volume expansions with the help of the homogenously distributed nanosized interspaces (porosities among the nanorods) present in the thin film.

Ionic Liquid‐Assisted Synthesis of Microporous Carbon Nanosheets for Use in High Rate and Long Cycle Life Supercapacitors

Microporous carbon sheets with precisely controlled thickness, narrow pores, short diffusion paths, high electrical conductive networks, and good wettability are synthesized using very low amounts of graphene sheets as a shape-directing agent via an ionic liquid-assisted surface coating method. When used as the electrode for supercapacitors, the sheets demonstrate excellent rate capability, good cycle stability, high specific capacitance, and high energy/power density.

Using a non-covalent modification to prepare a high electromagnetic interference shielding performance graphene nanosheet/water-borne polyurethane composite

We prepared flexible, lightweight, and high electromagnetic interference (EMI) shielding performance graphene nanosheet (GNS)/water-borne polyurethane (WPU) composites. WPU, with sulfonate functional groups, was used as the polymer matrix. By adsorbing the cationic surfactant (stearyl trimethyl ammonium chloride) on the surface of the GNSs (S-GNSs), restacking and aggregation of the GNSs have been efficiently suppressed, which also attracted sulfonate groups from the WPU matrix. Because of the favorable interfacial interactions arising from electrostatic attraction, the S-GNS exhibited good compatibility with the WPU matrix. Such a homogeneous dispersion contributed to the construction of an electrical conductive network. The S-GNS/WPU composite exhibited a low electrical conductivity percolation threshold and an outstanding enhanced electrical conductivity of approximately 5.1S/m. A high EMI shielding effectiveness of approximately 32dB was obtained by the WPU composites with contents of 5vol.% (approximately 7.7 wt.%) S-GNSs.

Micromechanics modeling of the electrical conductivity of carbon nanotube (CNT)–polymer nanocomposites

A mixed micromechanics model was developed to predict the overall electrical conductivity of carbon nanotube (CNT)–polymer nanocomposites. Two electrical conductivity mechanisms, electron hopping and conductive networks, were incorporated into the model by introducing an interphase layer and considering the effective aspect ratio of CNTs. It was found that the modeling results agree well with the experimental data for both single-wall carbon nanotube and multi-wall carbon nanotube based nanocomposites. Simulation results suggest that both electron hopping and conductive networks contribute to the electrical conductivity of the nanocomposites, while conductive networks become dominant as CNT volume fraction increases. It was also indicated that the sizes of CNTs have significant effects on the percolation threshold and the overall electrical conductivity of the nanocomposites. This developed model is expected to provide a more accurate prediction on the electrical conductivity of CNT–polymer nanocomposites and useful guidelines for the design and optimization of conductive polymer nanocomposites.

Experimental realization of simultaneous negative permittivity and permeability in Ag/Y3Fe5O12 random composites

Ag/Y3Fe5O12 random composites of silver particles randomly hosted in porous Y3Fe5O12 were prepared using a facile impregnation–calcination process. With the increase of silver content, the silver particles interconnected with each other near the percolation threshold, leading to the formation of electrical conductive silver networks. The plasma oscillation of delocalized electrons in interconnected silver particles leads to the negative permittivity. The negative permittivity behaviour was analyzed using the Drude model and equivalent circuit models. Meanwhile, the diamagnetic response of silver networks combined with the magnetic resonance of Y3Fe5O12 results in the negative permeability. That is to say, simultaneous negative permittivity and negative permeability were realized in the Ag/Y3Fe5O12 random composites. Hopefully, tunable double negative property could be realized by adjusting the microstructure and composition of the composites. External DC magnetic field could also be applied to control the electromagnetic properties of the composites.

Carbon-Coated Si Nanoparticles Dispersed in Carbon Nanotube Networks As Anode Material for Lithium-Ion Batteries

Si has the highest theoretical capacity among all known anode materials, but it suffers from the dramatic volume change upon repeated lithiation and delithiation processes. To overcome the severe volume changes, Si nanoparticles were first coated with a polymer-driven carbon layer, and then dispersed in a CNT network. In this unique structure, the carbon layer can improve electric conductivity and buffer the severe volume change, whereas the tangled CNT network is expected to provide additional mechanical strength to maintain the integrity of electrodes, stabilize the electric conductive network for active Si, and eventually lead to better cycling performance. Electrochemical test result indicates the carbon-coated Si nanoparticles dispersed in CNT networks show capacity retention of 70% after 40 cycles, which is much better than the carbon-coated Si nanoparticles without CNTs.

Si/C composite nanofibers with stable electric conductive network for use as durable lithium-ion battery anode

High-energy anode materials have attracted significant attention because of their potential applications in large-scale energy storage devices. However, they often suffer from rapid capacity fading due to the pulverization of the electrode and the breakdown of electric conductive network caused by the large volume changes of active material upon repeated lithium insertion and extraction. In this work, a new electrode composed of Si/C composite nanofibers was prepared, aiming at the improvement of cycling performance of Si anodes through the establishment of a stable electric conductive network for Si during cycling. By electrospinning, a three-dimensional network of carbon nanofibers, which possesses good elasticity to maintain the structure integrity and stable electric conductive network, is formed; by carbon coating, all Si nanoparticles are tightly bonded with carbon fibers to form a stable electric conductive pathway for electrode reactions. The nanofiber structure and the carbon coating on Si, combined with the binder, lead to a stable network structure that can accommodate the huge volume change of Si during the repeated volume expansion and contraction, thus resulting in excellent cycling performance.

The effect of molecular chain polarity on electric field-induced aligned conductive carbon nanotube network formation in polymer melt

Two ethylene–vinyl acetate (EVA) copolymers containing 10 and 25 wt.% vinyl acetate (EVA10 and EVA25) were utilized to explore the effect of molecular polarity on the formation of conductive carbon nanotube (CNT) network in EVA melt under an electric field. Because of the different interfacial energy, it was supposed to be stronger molecular chain-CNT interaction in CNT/EVA25 than that in CNT/EVA10. The critical time for conductive CNT network formation decreased with annealing temperature, filler loading and EVA polarity. The activation energy of conductive CNT network formation (93.9 kJ/mol) in CNT/EVA10 is lower than that (104.7 kJ/mol) in CNT/EVA25. By a thermodynamic percolation model, the percolation threshold at the equilibrium state was about 0.19 vol.% for CNT/EVA10, while it rose to 0.27 vol.% for CNT/EVA25. Morphological observation showed a high degree of CNT alignment in CNT/EVA10 compared to CNT/EVA25 after application of an electric field. The results suggested the strong CNT–EVA chain interaction and higher viscosity of polymer matrix limited the CNT alignment and the conductive network tended to form easily in EVA melt with a low chain polarity.

Electric Conductive Si<sub>3</sub>N<sub>4</sub>/TiN Composite Ceramic Manufactured by Liquid-Qhase Sintering

Si3N4 based electric conductive ceramics were fabricated by pressureless liquid phase sintering with La2O3-AlN and TiN as sintering and conductive additives. The Si3N4 powder was synthesized by SHS (self-propagation high-temperature synthesis) method. The bulk density, mechanical properties and electrical conductivity of the sintered samples were studied. Microstructure and phase composition were analyzed by SEM and XRD. The results show that the density of the samples is above 96%. The sintered samples consist of β-Sialon and the conductive phase. β-Sialon grains shows elongated and the conductive phase granular which formed electric conductive network. The sintered samples have good mechanical properties and its electric resistivity is from 1012 Ω•cm above drop to 1 Ω•cm below.

Effect of oxyfluorinated multi-walled carbon nanotube additives on positive temperature coefficient/negative temperature coefficient behavior in high-density polyethylene polymeric switches

Multi-walled carbon nanotubes (MWCNTs) were embedded into high-density polyethylene (HDPE) to improve the electrical properties of HDPE polymeric switches. The MWCNT surfaces were modified by oxyfluorination to improve their positive temperature coefficient (PTC) and negative temperature coefficient (NTC) behaviors in HDPE polymeric switches. HDPE polymeric switches exhibit poor electron mobility between MWCNT particles when the number of oxygen functional groups is increased by oxyfluorination. Thus, the PTC intensity of HDPE polymeric switches was increased by the destruction of the electrical conductivity network. The oxyfluorination of MWCNTs also leads to weak NTC behavior in the MWCNT-filled HDPE polymeric switches. This result is attributed to the reduction of the mutual attraction between the MWCNT particles at the melting temperature of HDPE, which results from a decrease in the surface free energy of the C–F bond in MWCNT particles.

The influence of gravity on the distribution of the deposit formed onto a substrate by sessile, hanging, and sandwiched hanging drop evaporation

The focus of the present article is the study of the influence of gravity on the particle deposition profiles on a solid substrate during the evaporation of sessile, hanging and sandwiched hanging drops of colloidal particle suspensions. For concentrations of nanoparticles in the colloidal solutions in the range 0.0001–1 wt.%, highly diluted suspensions will preferentially form rings while concentrated suspensions will preferentially form spots in both sessile and hanging drop evaporation. For intermediary concentrations, the particle deposition profiles will depend on the nanoparticle aggregation dynamics in the suspension during the evaporation process, gravity and on the detailed evaporation geometry. The evaporation of a drop of toluene/carbon nanoparticle suspension hanging from a pendant water drop will leave on the substrate a circular spot with no visible external ring. By contrast, a clear external ring is formed on the substrate by the sessile evaporation of a similar drop of suspension sandwiched between a water drop and the substrate. From the application viewpoint, these processes can be used to create preferential electrical conductive carbon networks and contacts for arrays of self-assembled nanostructures fabricated on solid substrates as well as on flexible polymeric substrates.

Composite Film Cathodes of Nanobeam V2O5 and Conductive Polymer for Lithium Batteries

Flexible composite films of nanobeam V2O5 and conductive polymer have been grown using the facile electrochemical polymerization method, which involves the application of anodic polymerization potential to the substrate electrode with the dispersed nanobeam V2O5 in solutions containing monomer - pyrrole or EDOT. For the case of pyrrole: V2O5 nanobeams can be thoroughly coated with polypyrrole, by taking advantage of the oxidative catalytic action of V2O5 in pyrrole polymerization. For the case of EDOT: since the advantage of V2O5 oxidative catalytic action is not applicable to PEDOT, it had been copolymerized with a surfactant p-TSA to achieve thorough and smooth coating of V2O5 nanobeams. Thus produced conductive polymers have shown to connect the isolated V2O5 nanobeam structures and provide valid electrical conductive networks for the cathode electrodes. These polymers enhanced the accessibility and diffusability of Li+ ions, thereby enabled V2O5/PPy and V2O5/PEDOT nanobeam composite film cathodes to have excellent cycling stability.

Effect of carboxylate multi-walled carbon nanotubes on the performance of thermoplastic starch nanocomposites

A facile solution dispersion method is used to prepare high performance thermoplastic starch (TPS)/carboxylate multi-walled carbon nanotubes (CMWNTs) nanocomposites. Transmission electron microscopy demonstrates glycerol pretreatment can further restrain the agglomeration of CMWNTs. So the improved dispersion and hydrophilicity of CMWNTs are favorable to enhance the compatibility and homogeneity of TPS/CMWNTs nanocomposites. The improvements of CMWNTs content enhance both the pasting viscosity of cornstarch and thermal stability of TPS matrix proved by rapid visco analysis and thermogravimetric analysis, respectively. Scanning electron microscopy reveals that homogeneous TPS/CMWNTs nanocomposites can be achieved when CMWNTs content is below 1.5 wt%. CMWNTs can also form a perfect electric conductive network in TPS matrix at this concentration. However, higher CMWNTs content deteriorate the plasticization of cornstarch detected by Fourier transform infrared. Therefore, mechanical test shows that the residue cornstarch granules influence the load transfer from TPS matrix to the ultra-strong carbon nanotubes (CNTs).

Influence of shear deformation on carbon nanotube networks in polycarbonate melts: Interplay between build-up and destruction of agglomerates

Shear-induced destruction and formation of conductive and mechanical filler networks formed by multi-wall carbon nanotubes in polycarbonate melts were investigated by simultaneous time-resolved measurements of electrical conductivity and rheological properties under steady shear and in the quiescent melt. The steady shear experiments were performed at shear rates between 0.02 and 1rad/s and for nanotube concentrations ranging from 0.5 to 1.5wt%. The influence of thermo-mechanical history on the state of nanotube dispersion and agglomeration was studied in detail.For melts with well-dispersed nanotubes a shear-induced insulator–conductor transition was observed, which is explained by the agglomeration of nanotubes under steady shear and the formation of an electrical conductive network of interconnected agglomerates. Simultaneously, a drastic decrease of the shear modulus (G∗=G′+iG″) during steady shear was observed, which can be related to a reduction of mechanical reinforcement due to agglomeration of dispersed nanotubes. These findings indicate a substantial difference in the nature of “electrical” and “mechanical” network and contradict earlier assumptions that steady (or transient) shear is always destructive for the conductive filler network in highly viscous polymer composites.It was also shown that after a certain time of steady shear the filler network asymptotically reaches its steady state characterized by the constant electrical conductivity and shear modulus of the composite melt. Such asymptotic behaviour of composite properties was experimentally shown to be related to the interplay of the destructive and build-up effects of steady shear. For modelling of the electrical conductivity in presence of steady shear a kinetic equation was proposed for filler agglomeration with shear-dependent destruction and build-up terms. This equation was coupled to the generalized effective medium (GEM) approximation for insulator–conductor transition.

Multiwalled Carbon Nanotubes-Incorporated Polyurethane Nanocomposites

Polyurethane was used as adhesive due to high reactivity, high flexibility, and mechanical properties. Electrically conductive adhesives (ECAs) are an alternative to tin-lead solder in order to provide conductive paths between two electrical device components, which typically consist of a polymeric resin that contributes physical and mechanical properties, and conductive fillers. However, ECAs have low electrical conductivity and unstable network due to large contact points of the few micrometer-sized metal particles. In order to overcome these restrictions, multiwalled carbon nanotubes (MWCNTs) with high aspect ratio and smaller nanometer scale can be used as conductive fillers. In this study, ECAs were based on polyurethane filled with two kinds of fillers, raw MWCNTs and acid treated MWCNTs, respectively. Electrical conductivity was measured by using four-point probe. Morphology and dispersibility of fillers were observed by scanning electron microscopy and transmission electron microscopy.

Synthesis and electrochemical properties of Li 4Ti 5O 12/C composite by the PVB rheological phase method

Spinel Li 4Ti 5O 12/C powders were synthesized successfully by a simple rheological phase method using polyvinylbutyral (PVB) as both template and carbon source. The structure and morphology characteristics of the composite were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy and transmission electron microscopy. The XRD results showed that the composite had a good crystallinity. Its average particle size was about 2.1 μm with a narrow size distribution as a result of homogeneous mixing of the precursors. The in situ carbon coating produced by decomposition of PVB played an important role in improving electrical conductivity, thereby enhancing the rate capacity of Li 4Ti 5O 12 as anode material in Li-ion batteries. The Li 4Ti 5O 12/C composite, synthesized at 800 °C for 15 h under argon, containing 0.98 wt% of carbon, exhibited better electrochemical properties in comparison with the pristine Li 4Ti 5O 12, which could be attributed to the enhanced electrical conductive network of the carbon coating on the particle surface.

Emulsion synthesis of nanoparticles containing PEDOT using conducting polymeric surfactant: Synergy for colloid stability and intercalation doping

AbstractPoly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is a widely used conductive aqueous dispersion synthesized by using emulsion polymerization method. To further enhance its solution processability and conductivity of PEDOT derivatives, we proposed to replace the nonconductive PSS with conductive poly[2‐(3thienyl)‐ethoxy‐4‐butylsulfonate] (PTEB) as surfactant for the emulsion polymerization of PEDOT. The reaction involved colloid stabilization and doping in one step, and yielded PEDOT:PTEB composite nanoparticles with high electrical conductivity. Contrary to its counterpart containing nonconductive surfactant, PEDOT: PTEB showed increasing film conductivity with increasing PTEB concentration. The result demonstrates the formation of efficient electrical conduction network formed by the fully conductive latex nanoparticles. The addition of PTEB for EDOT polymerization significantly reduced the size of composite particles, formed stable spherical particles, enhanced thermal stability, crystallinity, and conductivity of PEDOT:PTEB composite. Evidence from UV–VIS and FTIR measurement showed that strong molecular interaction between PTEB and PEDOT resulted in the doping of PEDOT chains. X‐ray analysis further demonstrated that PTEB chains were intercalated in the layered crystal structure of PEDOT. The emulsion polymerization of EDOT using conducting surfactant, PTEB demonstrated the synergistic effect of PTEB on colloid stability and intercalation doping of PEDOT during polymerization resulting in significant conductivity improvement of PEDOT composite nanoparticles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2536–2548, 2008

Skin-Core Micro-Structure and Surface Orientation of Carbon Nanotube Composites by Injection Molding Process

Multi-walled carbon nanotube (MWNT) was filled into poly (ethylene terephthalate) (PET) matrix and MWNT/PET composite was prepared by injection molding process. The microstructure and electrical conductive property were investigated carefully. After injection molding, the electrical conductivity of injected sample decreased sharply because of the orientation of CNT due to strong shearing force. The electrical conductive network of CNT had been destroyed after orientation of CNT. Because of the difference of shearing rate between the surface and the body center during the injection molding process, a skin-core structure emerged. Near the surface, the injected sample has higher degree of orientation of CNT and higher electrical resistance.