Interfacial Electrical Resistance Research Articles

Interface of gallium-based liquid metals: oxide skin, wetting, and applications.

Gallium-based liquid metals (GaLMs) are promising for a variety of applications-especially as a component material for soft devices-due to their fluidic nature, low toxicity and reactivity, and high electrical and thermal conductivity comparable to solid counterparts. Understanding the interfacial properties and behaviors of GaLMs in different environments is crucial for most applications. When exposed to air or water, GaLMs form a gallium oxide layer with nanoscale thickness. This "oxide nano-skin" passivates the metal surface and allows for the formation of stable microstructures and films despite the high-surface tension of liquid metal. The oxide skin easily adheres to most smooth surfaces. While it enables effective printing and patterning of the GaLMs, it can also make the metals challenging to handle because it adheres to most surfaces. The oxide also affects the interfacial electrical resistance of the metals. Its formation, thickness, and composition can be chemically or electrochemically controlled, altering the physical, chemical, and electrical properties of the metal interface. Without the oxide, GaLMs wet metallic surfaces but do not wet non-metallic substrates such as polymers. The topography of the underlying surface further influences the wetting characteristics of the metals. This review outlines the interfacial attributes of GaLMs in air, water, and other environments and discusses relevant applications based on interfacial engineering. The effect of surface topography on the wetting behaviors of the GaLMs is also discussed. Finally, we suggest important research topics for a better understanding of the GaLMs interface.

Lithium-Sulphur Batteries – Their Equivalent Circuit Model and How Electrochemical Conductivity Impacts Resistivity and Capacity Fading

Electrochemical impedance spectroscopy (EIS) was used to investigate the Lithium Sulfur battery's electrochemical dynamics. An equivalent circuit model was created using temperature and discharge depth data from EIS spectra. The mechanism of Lithium Sulfur batteries' capacity depletion was then studied by tracking the change in impedance during cycling. According to the findings, the charge-transfer mechanism is responsible for the EIS spectrum's semicircle at intermediate frequencies, whereas the high-frequency semicircle is linked to the interfacial electrical resistance. Additionally, the key significant contributor to the capacity fading of Lithium Sulfur batteries' is the charge-transfer impedance, whereas electrolyte resistance and interphase contact resistance also fluctuate with cycle number, albeit in different ways.

Unravelling Effective-Medium transport and interfacial resistance in (CaTe)x(GeTe)100-x thermoelectrics

This work reports an exotic group of (CaTe)x(GeTe)100-x thermoelectric materials, which compromise the composite of CaTe nanoinclusions and GeTe matrix. By incrementing Ca fraction, the figure-of-merit of GeTe is enhanced from 0.9 to 2.0 in nominal (CaTe)8(GeTe)92 at 800 K, referring to a heat-to-electricity efficiency of 9.7 % under a temperature difference of 500 K. Density-functional theory calculation and effective-medium theory modelling are used to ascribe the exceptional thermoelectric properties to two effective mechanisms. First, alloying Ca depopulates the Ge vacancies in GeTe via elevating the formation energy, which optimizes carrier concentration to secure a large power factor of 44.3 μW∙cm−1∙K−2. Second, densely distributed CaTe nanoprecipitates can contribute to additional effective-medium transport, while also manipulate interfacial electrical and thermal resistance due to energy filtering and phonon diffusion-mismatch effects, which decreases thermal conductivity to 1.8 W∙m−1∙K−1. The present work with reasonably increased figure-of-merit and conversion efficiency can inspire future investigations towards high-performance GeTe thermoelectrics.

Multi-physics electrical contact analysis considering the electrical resistance and Joule heating

A multi-physics electrical contact model is developed to predict the contact pressure, temperature, and electric current density (ECD) distributions on the contact surface. The theoretical model takes the interfacial electrical resistance and its resultant Joule heating into account. The contact pressure and contact radius are calculated by solving the first kind of Cauchy singular integral equation. The temperature and ECD are obtained based on the obtained contact pressure. Then, a three-dimensional finite element model is established to simulate the mechanical, thermal, and electrical behaviors of electrical contact. The finite element model can consider both the interfacial electrical resistance and the constriction electrical resistance. The theoretical results of the electrical contact behaviors are compared with the numerical results. The influences of the electrical resistance, normal force, electric potential, and distribution form of the heat flux on the contact pressure, temperature, and ECD distributions are investigated. The results indicate that the proposed multi-physics contact model can provide an accurate prediction of electrical contact behaviors.

Grain boundary engineered, multilayer graphene incorporated LaCoO3 composites with enhanced thermoelectric properties

Enhancement of thermoelectric properties by virtue of decreased electrical resistance through grain boundary engineering is realised in this study. A robust strategy of optimisation of the transport properties by tuning the energy filtering effects at the interfaces by decreasing the interfacial electrical resistance is achieved in LaCoO 3 (LCO). This is accomplished by the incorporation of multilayer graphene within the parent LCO matrix containing multi-scale nano/micro grains. The present work has attained a substantial increment in electrical conductivity from a value of 96 Scm -1 for bare LCO to ∼5300 Scm -1 at 750 K by incorporating 0.08 wt% multilayer graphene in LCO. No significant change in thermal conductivity is observed due to the presence of multilayer graphene in LCO. A zT of 0.33 at 550 K for 0.08 wt% multi-layer graphene incorporated LCO composite is achieved which is the highest thermoelectric figure of merit value for undoped LCO reported until now.

Improvement for electrical conductivity of Ti3SiC2/Cu joint brazed with a novel Sn6Ag7Ni4Co2Ti low-melting high entropy alloy filler

Reducing the interfacial electrical resistance of Ti3SiC2/Cu joint has significant value to promote its application in the field of electrical contact. In the study, a novel Sn6Ag7Ni4Co2Ti low-melting high entropy alloy (HEA) was designed and fabricated, and a sound Ti3SiC2/Cu brazed joint was obtained using above filler. The interface of Ti3SiC2/Cu joint brazed with Sn6Ag7Ni4Co2Ti filler is mainly composed of Ag(s,s), Cu(s,s) and a few (Ni, Co)2Si. Compared with Ti3SiC2/Cu joint brazed with Ag-26.7Cu-4.5Ti filler, the electrical resistance of the joint brazed with Sn6Ag7Ni4Co2Ti filler is lower at all test temperatures, which is reduced by up to 15.99% when the test temperature is 300 °C.

A hierarchical design for thermoelectric hybrid materials: Bi2Te3 particles covered by partial Au skins enhance thermoelectric performance in sticky thermoelectric materials

Sticky thermoelectric (TE) materials have been inversely designed to enable the mass production of flexible TE sheets through lamination or roll-to-roll processes without using electrically conductive adhesives. They have also been demonstrated as inorganic/organic hybrid materials consisting of TE inorganic particles and low-volatilizable organic solvents to exhibit Seebeck coefficients based on the TE particles and low thermal conductivities based on the organic matrix. To achieve energy harvesting of 250 µW for driving various electric devices using voltage boosters, herein, we employ p- and n-type Bi2Te3 particles due to their high Seebeck coefficients, and cover the Bi2Te3 bodies with Au skins because the interfacial electrical resistance depends on the electrical resistance of opposing substances at the interface. After controlling the plating amount to cover the Bi2Te3 particles with Au skins, we achieve a TE power generation two orders of magnitude greater than the previous study, i.e., 255 µW on a hot plate of 110 °C with a 6 × 6 module. Overall, with input from other organic devices, like organic light-emitting diodes and dye-sensitized solar cells, this study presents a hierarchical design for TE hybrid materials that suppresses the thermal conduction by hybridizing TE particles with the organic matrix at the microscale. This reduces the electrical resistance by modifying the interfaces of the TE particles at the nanoscale and optimizes the Seebeck coefficient of TE particles at the atomic scale. To compete with solid-state TE modules with regards to power generation capacity, the hierarchical design towards a possible further two orders of magnitude improvement is also discussed.

Effects of interfacial properties on conversion efficiency of Bi2Te3-based segmented thermoelectric devices

The conversion efficiency η of a thermoelectric (TE) device can be effectively improved by constructing segmented TE legs, but the specific interfaces between the heterogeneous materials inevitably degrade the performance. Focusing on the Bi2Te3-based two-segmented module, we systematically investigated the influences of the Peltier effect, interfacial electrical resistance Re, and interfacial thermal resistance Rt on the conversion efficiency η. It is found that the Peltier heat can increase the conversion efficiency if the Seebeck coefficient increases along the direction of an electric current. An applicable Re should be kept on the order of magnitudes of 10−5 Ω cm2 for segmented TE devices, since the increased Re significantly decreases η. With a determined Re, η depends on the leg height L rather than the cross-sectional area A. In contrast, η is hardly affected by the variation in the interfacial thermal resistance Rt, while both the input heat flux Qin and output power P decrease with the increasing Rt.

Ultralight, flexible and conductive silver nanowire/nanofibrillated cellulose aerogel for multifunctional strain sensor

Wearable strain sensors have drawn growing interest in the field of intelligent electronic devices because of their inherent advantages including miniaturization and portability. For practical applications, strain sensors with lightness, flexibility, and high sensitivity are urgently desired. Herein, the interconnected silver nanowires (AgNWs) are assembled into the nanofibrillated cellulose (NFC) aerogel through unidirectional freeze-drying yielding an ultralight and conductive AgNWs/NFC aerogel (SNA) with ordered pore orientation. After thermal welding, the SNA possesses unique electron transfer channels, which can efficiently eliminate the interfacial electrical resistance at the AgNWs junctions and bring an impressive conductivity enhancement for the composite aerogel. Benefiting from the synergy of the desired microstructure and superior conductivity of as-prepared aerogel, the derived sensor shows desirable sensitivity (3.86 kPa−1), fast response time (180 ms), ultralow density (less than 13.58 mg/cm3) and detection limit of 0.5% strain, and exceptional stability and durability (over 10,000 cycles). Significantly, the integrated conductive network in SNA simultaneously offers real-time monitoring of subtle deformations and electrophysiological signals, which enables the designs of wearable device, acoustic sensor, and vehicles’ speed and loading detector. The presented strategy opens up a new possibility for designing and manufacturing next-generation multifunctional strain sensor to bring the technology much closer to commercialization.

Electrical Impedance of V2O5/POMA Hybrid Film Deposited by Casting for Application in Ammonia Gas Sensor

The sensitivity evaluation of a vanadium pentoxide/poly-o-methoxyaniline hybrid material (V2O5/POMA) using casting deposition for the preparation of an ammonia gas sensor was investigated herein. V2O5/POMA was produced by the intercalation of V2O5 via sol–gel and o-methoxyaniline monomers. V2O5/POMA thin film deposition onto electrodes was performed by casting. The electrical studies confirmed that V2O5/POMA exhibited increased complex impedance as a function of increasing ammonia concentration. The conductivity of the film decreased with increasing ammonia concentration due to the de-doping process. According to theoretical adjustment, a significant increase in the bulk and interfacial electrical resistance in the presence of ammonia was observed. The combination of these effects contributed to the high sensitivity of the prepared film in both the real and imaginary components of the complex impedance for ammonia gas in a range of 0 to 100 ppm, which indicated that the film is a good candidate for use as an ammonia sensing material.

Oxygen-Induced Reversible Sn-Dopant Deactivation between Indium Tin Oxide and Single-Crystalline Oxide Nanowire Leading to Interfacial Switching.

An impurity doping in semiconductors is an important irreversible process of manipulating the electrical properties of advanced electron devices. Here, we report an unusual reversible dopant activation/deactivation phenomenon, which emerges at an interface between indium tin oxide (ITO) and single-crystalline oxide channel. We found that the interface electrical resistance between ITO electrodes and single-crystalline oxide nanowire channel can be repeatedly switched between a metallic state and a near-insulative state by applying thermal treatments in air or vacuum. Interestingly, this electrical switching phenomenon disappears when the oxide nanowire changes from the single-crystalline structure to the lithography-defined polycrystalline structure. Atmosphere-controlled annealing experiments reveal that atmospheric oxygen induces repeatable change in the interfacial electrical resistance. Systematic investigations on metal cation species and channel crystallinity demonstrate that the observed electrical switching is related to an interface-specific reversible Sn-dopant activation/deactivation of ITO electrode in contact with a single-crystalline oxide channel.

Polydopamine coated poly(m-phenylene isophthalamid) membrane as heat-tolerant separator for lithium-ion batteries

Poly(m-phenylene isophthalamide) (PMIA) membranes are promising heat-tolerant separator candidates of lithium-ion batteries (LIBs), while their wettability toward carbonate electrolyte and corresponding batteries performance are not desirable. Herein, PMIA membranes coated with ultrathin mussel-inspired polydopamine (PDA) layer were fabricated as separators in LIBs. The introduced amino, quinonyl, and catechol groups in PDA coating could enhance the wettability of the resultant PMIA-PDA separator toward electrolyte. The PMIA-PDA separator had excellent thermal stability, showing a thermal shrinkage of 5.2% at 200 °C. The contact angle of the thermal-treated PMIA-PDA separator could maintain at 26.1°, which decreased by 42.7% compared with the pristine PMIA separator. The PMIA-PDA separator also displayed a high ionic conductivity (0.86 mS cm−1) and a low interfacial electric resistance (62.4 Ω). Consequently, the assembled LiCoO2/PMIA-PDA/Li battery achieved good cyclic stability with the capacity retention of 84.3% (121.1 mAh g−1) after 100 cycles under 30 °C. More significantly, the relevant capacity retention remained at 89.0% (127.5 mAh g−1) under 60 °C, which implied a great potential of PMIA-PDA membranes as separators of high-safety LIBs.

Nano-silica-decorated Poly(m-Phenylene Isophthalamide) Separator with Enhanced Mechanical and Electrolyte Wetting Properties for Lithium-Ion Batteries

Heat-resistant poly(m-phenylene isophthalamide) (PMIA) has attracted considerable attention as a novel separator for application in lithium-ion batteries (LIBs); however, its mechanical strength and electrolyte wettability are not ideal. Herein, a nano-silica-decorated poly(m-phenylene isophthalamide) (PMIA@SiO2) separator was fabricated with SiO2 nanoparticles uniformly attached to the pores and pore walls of the PMIA separator. The as-prepared PMIA@SiO2 separator has good mechanical strength (a 16% improvement compared with pristine PMIA) and wettability toward the electrolyte (the contact angle decreases from 34.0° to 23.1°). The PMIA@SiO2 separator also had a high ionic conductivity (0.75 mS/cm) and low interfacial electric resistance (75 Ω). The assembled LiCoO2/PMIA@SiO2-liquid electrolyte/Li cell displays good cycle performance with a capacity retention of 88.1% after 50 cycles. Furthermore, the cycling performance and rate capacity rarely changed after high-temperature treatment. Therefore, the nano-silica-decorated PMIA separator is a potential candidate for application in LIBs with high safety.

Quantitative Analyses of the Interfacial Properties of Current Collectors at the Mesoscopic Level in Lithium Ion Batteries by Using Hierarchical Graphene.

At the mesoscopic level of commercial lithium ion battery (LIB), it is widely believed that the poor contacts between current collector (CC) and electrode materials (EM) lead to weak adhesions and large interfacial electric resistances. However, systematic quantitative analyses of the influence of the interfacial properties of CC are still scarce. Here, we built a model interface between CC and electrode materials by directly growing hierarchical graphene films on commercial Al foil CC, and we performed systematic quantitative studies of the interfacial properties therein. Our results show that the interfacial electric resistance dominates, i.e. ∼2 orders of magnitude higher than that of electrode materials. The interfacial resistance could be eliminated by hierarchical graphene interlayer. Cathode on CC with eliminated interfacial resistance could deliver much improved power density outputs. Our work quantifies the mesoscopic factors influencing the battery performance and offers practical guidelines of boosting the performance of LIBs and beyond.

Numerical simulation of weld nugget in resistance spot welding process

The resistance spot welding (RSW) stands different over other welding techniques as the actual weld nugget is shaped internally relative to the surface of the base metal. The weld formed is fundamentally a mix of heat, pressure and time. The welding conditions are precisely controlled to produce sound nuggets. The application of interface pressure allows accurate prediction of interfacial heat and electrical resistance, which plays a dominant role in Joule’s heat generation. In this work, lap welding using resistance spot welding has been numerically investigated for Mild steel (G-3302) and Stainless steel (SS-202) sheets. Spot welding has been completed by utilizing a 35 kVA DC type resistance spot welding machine, constrained by a Programmable Logic Controller unit. For both materials, two spots, three spots and four spots weld were done in order to obtain various comparative results. The weld nugget formation has been simulated using SIMULIA. The 3D model has been created by using GUI of commercial FEA package ABAQUS 6.14. The model employs coupled thermal-electrical-mechanical analysis. Simulation has been performed for pertinent parameters in ABAQUS 6.14. The obtained plots from numerical model are found to be in strong consistency with experimental data.

Experimental analysis of interfacial shear stress and electrical resistance of indium tin oxide-coated polyethylene terephthalate films for a whole folding test

The purpose of this study is to analyze the performance of the flexible conductive substrate by interfacial shear stress. This study performed automatic liquid-crystal modulating common-path interferometry (LMCI) optical inspections on 125-µm polyethylene terephthalate (PET) substrates having indium tin oxide (ITO) coating thicknesses of 80 nm, 160 nm, and 230 nm. The nonlinear characteristic of the stress-optical coefficient of the ITO material is obtained using LMCI. To validate the performance of the flexible conductive substrate, this study has utilized an automatic sliding-folding testing platform (ASTP) for a whole-folding test. Eventually, this study successfully has utilized interface shear stresses to validate the performance of the flexible conductive substrate depended on the different thicknesses of the conductive layers for whole-folding test by using LMCI and ASTP. According to the measurement results, as the folding radii decrease and the ITO thicknesses of ITO-coated PET substrates increase, the changes of interfacial shear stresses increase in compressive direction and the change-rates of electrical resistance of ITO-coated PET substrate also increase. Therefore, the interfacial shear stress measurement and analysis results depicted on flexible conductive substrates provide a validation for improving the manufacturing process and for reducing process residual stresses.

Breakdown of Native Oxide Enables Multifunctional, Free-Form Carbon Nanotube-Metal Hierarchical Architectures.

Passive oxide layers on metal substrates impose remarkable interfacial resistance for electron and phonon transport. Here, a scalable surface activation process is presented for the breakdown of the passive oxide layer and theformation of nanowire/nanopyramid structured surfaces on metal substrates, which enables high-efficiency catalysis of high-crystallinity carbon nanotubes (CNTs) and the direct integration of the CNT-metal hierarchical architectures withflexible free-form configurations. The CNT-metal hierarchical architecture facilitates a dielectric free-energy-carrier transport pathway and blocks the reformation of passive oxide layer, and thus demonstrates a 5-fold decrease in interfacial electrical resistance with 66% increase in specific surface area compared with those without surface activation. Moreover, the CNT-metal hierarchical architectures demonstrate omnidirectional blackbody photoabsorption with the reflectance of 1 × 10-5 over the range from ultraviolet to terahertz region, which is 1 order of magnitude lower than that of any previously reported broadband absorber material. The synergistically incorporated CNT-metal hierarchical architectures offer record-high broadband optical absorption with excellent electrical and structural properties as well as industrial-scaleproducibility.

Ultra-robust wide-range pressure sensor with fast response based on polyurethane foam doubly coated with conformal silicone rubber and CNT/TPU nanocomposites islands

Highly durable piezo-resistive pressure sensors with excellent repeatability and fast response were developed. The developed sensor have a characteristic of coated with silicone rubber, which has widened pressure measurement range and improved response time. The sensor is capable of measuring pressures lower than 100Pa and higher than 200 kPa and can measure oscillating pressure well above 50 Hz. The sensor showed high repeatability and durability and operated normally after 1000 cycles at 360 kPa applied pressure. The sensor was made by coating polyurethane foam with silicone rubber and further dip-coated with MWCNT dispersed TPU ink. The use of TPU as a binding material helped MWCNT strongly attach to the foam skeleton and reduced the interfacial electrical resistance. As a result, low hysteresis (6.4%) was achieved. By controlling amount of silicone rubber impregnated, the sensitivity can be controlled from 0.013 kPa−1 to 0.032 kPa−1. These sensors were used for measuring both subtle pressures such as the pulse and large pressures such as the pressure beneath a heel. Additionally, wide range of pressure distributions were measured using the array sensors. The economic value of this sensor is tremendous because it can be used in a wide pressure range where high repeatability and fast response are required.

Amorphous carbon films doped with silver and chromium to achieve ultra-low interfacial electrical resistance and long-term durability in the application of proton exchange membrane fuel cells

Amorphous carbon (a-C) films exhibit properties that make them attractive for a wide range of applications in automotive components. Proton exchange membrane fuel cells (PEMFCs) assembled by metallic bipolar plates (BPPs) are promising power sources for new energy vehicles. Harsh environments of PEMFCs require preparing coatings on metallic BPPs to achieve high corrosion resistance and electrical conductivity, and a-C based coatings have the great potential. However, their low stability and high internal stress significantly damage their durability. This work aims to develop a fundamental understanding of the effect of doping Ag and Cr on the performance and durability of a-C based coatings. Experimental results revealed that a-C films doped with Ag and Cr (a-C:Ag:Cr) simultaneously achieve ultra-low interfacial contact resistance (ICR), low internal stresses, and higher stabilities. We also developed an atomistic model by molecular dynamics (MD) to understand certain behaviors of a-C:Ag:Cr. The ultra-low ICR was mainly attributed to Ag nanoclusters embedded in a-C phases, low hardness, and a more graphite-like structure. The enhanced stability was attributed to denser structures and lower internal stresses. MD simulations suggested that the effect of doping Ag or Cr on the surface morphology and internal stress of a-C films may have different mechanisms.

Vertically-Aligned Carbon Nanotube Arrays as Binder-Free Supports for Nickel Cobaltite based Faradaic Supercapacitor Electrodes

Faradaic supercapacitors have been proposed as energy storage devices capable of providing both high energy and power densities. The exceptional attributes of high specific surface area and good electrical properties displayed by vertically aligned carbon nanotube (VACNT) arrays make them a promising candidate as faradaic capacitive electrode supports. However, some drawbacks to their use and performance exist including their resistance to wetting by an aqueous electrolyte solution, bad electrical continuity at the array/electrode base interface for binder-free applications, and potential collapse of the VACNT array because of capillary forces. This study explores possible solutions to these challenges by growing the arrays directly on conducting electrodes thus reducing the interfacial electrical resistance and removing the need for binders, using a combined plasma and forced vacuum wetting procedure to improve the wetting behavior, using a pulsed electrodeposition technique to obtain a uniform distribution of faradaic capacitive material (nickel cobaltite), and using freeze drying to prevent the collapse of the VACNT array’s native pore structure after electrodeposition. A specific capacitance of 970 Fg−1 at 2 Ag−1 is measured for the fabricated electrode with excellent performance (>80% retained capacity) over 3000 charge-discharge cycles.