Conductive Powder Research Articles

Charge-Discharge Mechanism of All-Solid-State Batteries Using Li2RuO3-Li2so4 Positive Electrode Active Materials

All-solid-state batteries have attracted great attention because of their high safety owing to the use of non-flammable inorganic solid electrolytes. Solid electrolytes with an extremely high ionic conductivity have already been discovered, and therefore the discovery of new and efficient electrode materials is key for the construction of high energy density all-solid-state batteries. In the electrode layers for conventional all-solid-state batteries, mixtures composed of active material, solid electrolyte and carbon conductive additive powders are often applied to secure lithium ionic and electronic conduction pathways. Moreover, most of all-solid-state batteries reported so far comprise a thin electrode layer with a small amount of active materials and a thick electrolyte layer as the separator. Therefore, the energy density of all-solid-state batteries at the present stage is considerably lower than that of typical lithium ion batteries. To enhance the energy density of all-solid-state batteries, high capacity electrode materials should be developed and the active material content should be increased in the composite electrode layers. With consideration to the demands and features described above, we have successfully developed a novel Li2Ru0.8S0.2O3.2 (80Li2RuO3·20Li2SO4 in mol%) positive electrode material for all-solid-state batteries. Mechanochemical treatment with Li2SO4 imparts ionic conductivity and favourable ductility to the Li2RuO3 active material. Because of the favourable formability and high electronic and ionic conductivities, we achieved the fabrication of all-solid-state cells, where the positive electrode layer was composed of the active material without any conductive additives. The all-solid-state cell using a monolithic Li2Ru0.8S0.2O3.2 positive electrode functioned as a secondary battery showing a high reversible capacity of about 270 mAh g-1. In this study, the detail charge-discharge mechanism of the Li2Ru0.8S0.2O3.2 positive electrode was investigated by XRD, TEM, XPS, and XAFS measurements.

Preparation and characterization of Ni-Cu composite nanoparticles for conductive paints

Abstract Ni and Cu are the two most promising alternatives to noble metals used in electrical conductive materials. However, Cu is susceptible to oxidation, while Ni exhibits poorer electrical conductivity. To solve this problem, Cu-Ni composite nanoparticles have been prepared in the present work by successive hydrazine reduction based on the different oxidation potential between Cu (II) and Ni (II). The as-prepared products were characterized by XRD, FE-SEM, EDS, and TG, and the electrical resistivity of which was measured by four-probe method. A formation process of the composite particles was proposed and demonstrated. The Cu-Ni composite nanoparticles have a uniform diameter of about 50nm, and exhibit higher oxidation temperature than Cu and lower electrical resistivity than Ni. This novel Ni-Cu structure and method might help solve the problems associated with the oxidation of Cu and the low electrical conductivity of Ni, which would further promote the application of base metal conductive powders.

Scalable chemical synthesis of doped silicon nanowires for energy applications.

A versatile, low-cost and easily scalable synthesis method is presented for producing silicon nanowires (SiNWs) as a pure powder. It applies air-stable diphenylsilane as a Si source and gold nanoparticles as a catalyst and takes place in a sealed reactor at 420 °C (pressure <10 bar). Micron-sized NaCl particles, acting as a sacrificial support for the catalyst particles during NW growth, can simply be removed with water during purification. This process gives access to SiNWs of precisely controlled diameters in the range of 10 ± 3 nm with a high production yield per reactor volume (1 mg cm-3). The reaction was scaled up to 500 mg of SiNWs without altering the morphology or diameter. Adding diphenylphosphine results in SiNW n-type doping as confirmed by ESR spectroscopy and EDX analyses. The measured SiNW doping level closely follows the initial dopant concentration. Doping induces both an increase in diameter and a sharp increase of electrical conductivity for P concentrations >0.4%. When used in symmetric supercapacitor devices, 1% P-doped SiNWs exhibit an areal capacity of 0.25 mF cm-2 and retention of 80% of the initial capacitance after one million cycles, demonstrating excellent cycling stability of the SiNW electrodes in the presence of organic electrolytes.

Pulsed electrodischarged pressure sintering and flash sintering, a review

Abstract Electric current activated/assisted sintering (ECAS) is a growing class of versatile techniques for sintering particulate materials. Nowadays, most of the scientific attention is focused on pulsed electric current sintering known as spark plasma sintering (SPS). SPS has been successfully applied to electrically conductive and low-electrical-conductivity ceramics although the measured temperature is not directly related to the sintering temperature. Here, we summarize the present status and problems of SPS technology, and introduce our approach to develop SPS. Then, as a future direction, we will demonstrate flash sintering using SPS furnace and conductive powders.

Characteristic Analysis of Three Dimensional Electrostatic Adhesion Mechanism based on Jamming Phenomenon of Conductive Powder

Characteristic Analysis of Three Dimensional Electrostatic Adhesion Mechanism based on Jamming Phenomenon of Conductive Powder

A review of performance optimization and current research in PMEDM

Abstract The EDM method is non-conventional in machining for machining of geometrically unpredictable or hard materials and electrically conductive materials that cannot be machined with ordinary forms of machining. With latest strategies, research has emphasized EDM's increased machining efficiency. PMEDM is an ongoing method where a Mixed conductive powder with the dielectric liquid to improve EDM machining capabilities in this direction. This paper introduces the review work done to improve the performance characteristics of machining like MRR, SR and TWR for different Machining parameters like Ip, Duty factor, Ton, Toff, Work piece material, powder type, concentrated powder with different dielectric liquids and powder materials. Also in the paper reports and summaries Current trends in the research, PMEDM using various powders such as Nano powders mixed in dielectric fluids and examined the current challenges, future scope of research and impediments of the PMEDM process.

A novel highly electrically conductive composite resin for stereolithography

The use of 3D printing for scientific and industrial applications is rapidly increasing and, simultaneously, is growing the interest toward printable smart materials. It is known that using a conductive filler, e.g. nanoparticles, metal powders or composite polymers, it is possible to produce a more electrically conductive printable material. The PEDOT:PSS polymer has been used extensively, from bioelectronics to energy storage devices, for its conductivity and biocompatibility. In this work, a highly electrically conductive resin for Stereolithography was developed using a dispersion of PEDOT particles, extracted from Clevios™ PH1000 through a simple separation process, in a PEGDA matrix. The resin composition was optimized in terms of photoinitiator, surfactant and filler concentration. Furthermore, optimal printing parameters were determined for this composite resin, obtaining a printed object with appreciable electrical conductivity (0.05 S cm−1) and mechanical properties (Young modulus 21 MPa).

Heterophase materials for fused filament fabrication of structural electronics

In this work, new electrically conductive composite filaments are developed for the fabrication of conductive paths, 3D printed with FDM technology. These composite materials consist of electrically conductive copper powder and a polymer matrix. The influence of three different polymers (ABS, PLA, PS) on the electrical properties of the composites was examined. Electrical measurements of the composite filaments with the increasing copper powder concentrations, allow identifying the percolation threshold for elaborated composites. Results show that the lowest resistivity (0.156 × 10−5 Ωm) was achieved for the ABS/Cu composite at the 84.6 wt% Cu concentration. The obtained resistivity values are much lower than for other conductive composites and nanocomposites filaments reported in the literature. Voltage-current characteristics determined for each composite material showed that composites have Ohmic characteristics in low voltage regime. At high voltage regime, the electrical power dissipated in the composites caused a rapid increase in temperature. It was discovered that a polymer matrix influences the maximum value of the electrical power that can be dissipated in the filament before losing electrical conductivity. Examples of conductive 3D printed structures made from elaborated composites are also presented.

Potential-Controlled Tensiometry: A Tool for Understanding Wetting and Surface Properties of Conductive Powders by Electroimbibition.

Potential-controlled tensiometry is a voltage-induced method which enables measuring the contact angle between a powder bed and a liquid medium through the capillary rise method. This analytical tool provides a fine-grained technique for understanding wetting behavior of powders as well as solid surfaces in connection with the application of an electrical potential. In this work, the powder bed was brought into contact with an aluminum rod connected to a portable lightweight DAC-module (digital to analog converter) powered by a lithium-polymer battery (LiPo). The presented analytical device can be charged up to ±1000 mV. Both the power source and the DAC-module are lightweight in order to be conveniently attached to a force tensiometer without incorporating complex wiring. In this setup, we tested multiwall carbon nanotubes (MWCNT) and glassy carbon particles. An influence of the potential on the wetting behavior of glassy carbon particles is observed which demonstrates the working principle of the device. Surprisingly, no significant effect of the potential on the wetting behavior of MWCNT is indicated in the range studied. This technique can be a valuable tool to analyze the effect of changing surface properties applying electrical gradients on materials.

Application methods for graphite as catalyzer in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) belong to the possible technologies on which future clean energy harvesting can be based. Opposite to silicon-based photovoltaics, DSSCs can be produced purely from non-toxic, inexpensive materials. Nevertheless, nowadays most research is performed aiming at increasing the efficiency of DSSCs based on (mostly toxic) ruthenium dyes or perovskites. In this paper, examinations include only non-toxic substances due to the planned subsequent use in textile fabrics, i.e. to TiO2, graphite, iodine/tri-iodide as electrolyte and an anthocyanin dye. Different application methods for the graphite layer of DSSCs were compared, focusing on such techniques which could also be applied on textile fabrics. A mixture of conductive silicone rubber and graphite powder resulted in the highest efficiencies, as compared to graphite pen, graphite spray, and coating with graphite flakes. In comparison to DSSCs with a pencil-made graphite layer, the power density could be increased by a factor of 2 by the new composite material.

Electromagnetic field effects in the microwave sintering of electrically conductive powders

Rapid sintering of compacted electrically conductive powders under heating by intense microwave radiation is investigated within a one-dimensional simulation model. The model accounts for the effective dielectric and magnetic properties of the powder material, electromagnetic field distribution, heat losses by thermal radiation, and densification. It is demonstrated that metal powders with insulating boundary layers on particles have low dielectric and magnetic losses, which results in a resonant character of microwave absorption. The influence of the interparticle contacts is investigated by introducing an effective electrical conductivity of the boundary layers, which can depend on the density. It is demonstrated that the losses in the boundary layers can stabilize the microwave heating process, facilitating rapid densification.

A novel inexpensive conductive material: Er-modified maifanite by gaseous penetration technology

Aiming to solve the problem of corrosion and high cost of the conductive fillers, the powders with the properties of anti-oxidation, corrosion resistance and thermal stability should be developed. A new modification technology, rare earth gaseous penetration, was applied to enhance the conductivity of maifanite in this paper, and the mechanism for improving the conductivity of maifanite effectively was speculated in detail for the variations of the composition, structure and morphology between the original and Er-penetration maifanite powders. The results of the resistivity show that Er-penetration can really improve the conductivity of maifanite powders. When the penetration temperature is 500 °C, the resistivity of maifanite surprisingly declines to 93.2 Ω·m. Moreover, XRD and XPS patterns display that the cations in maifanite are substituted by Er3+ successfully, resulting in the production of electrons in the system, which is the key reason to heighten the conductivity of maifanite. Most importantly, Er-penetration maifanite, whose price is really low, can replace the expensive conductive powders and be used in the electronic industry to decrease the cost of the electronic devices.

Effect of deep cryotreated tungsten carbide electrode and SiC powder on EDM performance of AISI 304

Powder mixed electric discharge machining (PMEDM) is a further advancement of conventional EDM process in which electrically conductive powder is suspended in the dielectric fluid to enhance the material removal rate (MRR) along with the surface quality. Cryotreatment is introduced in this process for improving the cutting tool properties as well as tool life. In this investigation, EDM is performed for the machining of AISI 304 stainless steel using cryotreated double tempered tungsten carbide electrode when SiC powder is suspended in the kerosene dielectric. The influence of process parameters viz. pulse on time, peak current, duty cycle, gap voltage and powder concentration on tool wear rate (TWR), surface roughness (Ra), and MRR has been studied. Metallographic analysis was carried out for the machined surfaces. By the addition of powder concentration and cryotreated double tempered electrode, significant improvement in the machining efficiency has been found out. When cryotreated electrode used MRR, TWR and Ra decreased by 12%, 24% and 13.3%, respectively and when SiC powder used MRR increased by 23.2%, TWR and Ra decreased by about 25% and 14.2%, respectively.

Heterogeneity of grain refinement and texture formation during pulsed electric current sintering of conductive powder: A case study in copper powder

The heterogeneity of grain refinement and texture formation in conductive copper powder during pulsed electric current sintering have been investigated by means of microstructural analysis of the particle-contacting zone of the samples sintered with micron-sized powders. The particle-contacting region was indicated to experience a higher level of grain refinement than the particle center due to the inhomogeneous temperature distribution among the particle when pulsed electric current passed through. Meanwhile, two main textures of Cube (1 0 0)[0 0 1] texture and Goss (1 1 0)[0 0 1] texture were directly detected in the sintered Cu samples by a combination of electron backscatter diffraction and X-ray diffraction. Based on the experimental results, a feasible mechanism for the formation of texture during the pulsed electric current sintering has been proposed by considering the applied uniaxial pressure and pulsed electric current as well as the rearrangement of grains. In addition, the effects of heterogeneous grain refinement and texture formation on the tensile properties of the sintered Cu samples were also discussed based on the tensile properties and fractographic. These results would contribute to the basic understanding of the sintering mechanisms in pulsed electric current sintering process.

Simultaneous machining and surface alloying of AISI 1040 steel by electrical discharge machining with boron oxide powders

In PM/EDM, it is known that when used electrically conductive powders, highly homogeneous alloyed layers can be formed where the gap extends slightly more than using non-conductive powders and regulates spark discharge and machining voltage more uniform. Boron element is non-conductive but when alloyed with steel, materials with high abrasion and corrosion resistance are obtained. In this study, the effects of boron oxide powders addition into dielectric fluid on microstructure and hardness of steel workpiece in electrical discharge machining (EDM) were investigated. For this purpose, by using a prismatic steel workpiece and a copper electrode in kerosene mixed with boron oxide (B2O3) powders, the morphology of the machined specimens at different powder concentrations and pulse duration settings were observed and investigated. In addition, the micro hardness of the layers occurred as a result of EDM was measured and discussed. The highest surface hardness value of 941 HV is measured over machined specimen with B2O3 powder addition, whereas the lowest surface hardness value of 413 HV is measured.

Enhancing efficiency of field assisted sintering by advanced thermal insulation

The influence of advanced thermal insulation on energy consumption and temperature distribution during electric field assisted sintering of conductive stainless steel powder and non-conductive zirconia powder was investigated. Four types of tool setup were considered: i) without insulation, ii) with die wall insulation, iii) with additional insulation of die faces and iv) with spacers manufactured from carbon fiber reinforced carbon composite (CFRC). The influence of thermal insulation on energy consumption was experimentally studied for samples with diameter of 17 mm. The temperature distribution in samples with diameters of 17 mm, 50 mm and 150 mm was modeled using the Finite Element Method. The power consumed during dwell was almost half the value when die wall insulation was used. The additional insulation of die faces and the application of CFRC spacers provide a threefold decrease in power during sintering of steel powder and a fivefold reduction during sintering of zirconia powder. The advanced thermal insulation significantly homogenizes the temperature distribution within samples of small and medium size. The advanced thermal insulation provides a strong decrease in the temperature gradient inside large conductive sample with a diameter of 150 mm. However, insulation apparently cannot ensure acceptable temperature homogeneity within non-conductive parts of such diameter. The reason for this is the specific current path and related heat concentration near the sample edge.

Thermal, Electrical, and Mechanical Properties of Various Thermal Conductive Powder Filled Polyamide 6 Composite Materials for Thermal Management Applications

Thermal, Electrical, and Mechanical Properties of Various Thermal Conductive Powder Filled Polyamide 6 Composite Materials for Thermal Management Applications

Poly(propylene carbonate) Interpenetrating Cross-Linked Poly(ethylene glycol) Based Polymer Electrolyte for Solid-State Lithium Batteries

Solid polymer electrolyte based on semi-interpenetrating polymer network (s-IPN) was synthesized from the mixture of poly(propylene carbonate) (PPC), poly(ethylene glycol) methylether acrylate (PEGMEA), poly(ethylene glycol) diacrylate (PEGDA), and lithium bis(trifluoromethane)sulfonimide (LiTFSI) salt via one-pot thermal curing method. The crosslinker PEGDA content and salt concentration were optimized. The ionic conductivity, lithium-ion transference number and electrochemical stability window of the s-IPN electrolyte were correlated with its thermal and physical properties. Differential scanning calorimetry measurements have shown a low degree of crystallinity in this s-IPN electrolyte. The electrolyte with higher salt concentration has lower ionic conductivity, consistent with higher glass transition temperature of poly(ethylene glycol) chain. The ionic conductivity was further enhanced by dispersion of lithium-ion conductive ceramic powder, lithium lanthanum zirconate (LLZO) into the s-IPN matrix. The optimized s-IPN has potential as a baseline material for future solid-state electrolyte designs.

Exploring Alternative Polymer Compositions for Highly Conductive Solid Polymer Composite Electrolytes

Battery safety is increasingly at the forefront of consumer concerns, especially regarding electric vehicles. Current lithium ion battery technology utilizes liquid electrolytes, which have very high ionic conductivities but are extremely flammable. To improve safety, researchers are investigating replacing liquid electrolytes in lithium ion batteries with solid electrolytes. A promising approach is the use of solid polymer composite electrolytes where lithium conductive ceramic powders are dispersed into polymer electrolyte matrix. These materials are intended to improve lithium conductivities and mechanical properties relative to pure polymer electrolyte, lower manufacturing and battery cell construction costs relative to using pure ceramic electrolytes, and eliminate volatile and flammable electrolyte solvents. Currently, the archetypal polymer matrix used in composite electrolytes is polyethylene oxide (PEO). When mixed with lithium salts, such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and ceramics, such as Li7La3Zr2O12 (LLZO), PEO based composites have conductivities (~10-7 S/cm at room temperature) that are still insufficient for today’s applications. In addition, PEO tends to crystallize and has poor oxidative stability (decomposition ca. 4V). We are exploring poly(polyethylene glycol methyl ether methacrylate) (PEGMA) and polyethylene carbonate (PEC) as alternatives to PEO to address issues with crystallization and oxidative stability, respectively. Composite electrolytes are fabricated by blending bulk polymer with LiTFSI and LLZO powders. We have formed rubbery PEGMA-based composites with comparable conductivities (~10-7 S/cm at room temperature, 70 vol% polymer, 10:1 ethylene oxide:lithium). Lithium symmetric cycling was observed to be stable over 250 hours at 1C. We have also recently formed stand-alone PEC based composites with high conductivities (~10-6 S/cm at room temperature, 60 vol% polymer, 10:1 ethylene carbonate:lithium). Investigations into the origin of this high conductivity and measurements of electrochemical stability are currently underway.

Poly(propylene carbonate) Interpenetrating Cross-Linked Poly(ethylene glycol) Based Polymer Electrolyte for Solid-State Lithium Batteries

Lithium-ion conducting solid polymer electrolytes (SPEs) are promising materials to replace flammable liquid electrolytes to solve the safety and performance issues in conventional rechargeable lithium batteries [1]. Poly(ethylene oxide) (PEO) has been studied extensively as baseline materials for SPEs. It is well known that pure PEO crystallizes at room temperature, hampering lithium ion migration and resulting in low ionic conductivity. This drawback hinders PEO based SPEs applied in real battery configuration that usually requires ionic conductivity greater than 10-4 S cm-1 at 25 ℃. In general, suppression of polymer crystallinity is favorable for SPEs to enhance the ionic conductivity [2]. Here, we synthesized a semi-interpenetrating polymer network (s-IPN) from the mixture of poly(propylene carbonate) (PPC), poly(ethylene glycol) methylether acrylate (PEGMEA), poly(ethylene glycol) diacrylate (PEGDA), and lithium bis(trifluoromethane) sulfonimidate (LiTFSI) salt using one-pot thermal curing method. The amorphous PPC performs as film forming agent, whereas the crosslinked network with PEG pendants provides lithium conducting channel. The s-IPN architecture inhibits the phase segregation of two different polymers. Curing temperature, crosslinker PEGDA content and salt concentration were optimized carefully to attain a flexible film with ionic conductivity reaching 5×10-6 S cm-1 at ambient temperature. The ionic conductivity and working potential window were correlated with the thermal and physical properties of the s-IPN electrolytes. Differential scanning calorimetry measurements have shown a decrease in the crystallinity of the s-IPN electrolytes. The electrolyte with higher salt concentration has lower ionic conductivity, consistent with higher glass transition temperature of PEG chain. The ionic conductivity was further enhanced by incorporating lithium ion conductive ceramic powder, lithium lanthanum zirconate (LLZO) as a filler into the s-IPN matrix, even though LLZO aggregation occurred during film forming. The optimized s-IPN has potential as a baseline material for future solid-state electrolyte designs. Acknowledgements We gratefully acknowledge the financial support from the NASA MIRO Program #NNX15AP44A and the National Science Foundation under Award #162-6449.