Korea Electronics Technology Institute

A highly stretchable metal electrode is developed via the solution-processing of very long (>100 μm) metallic nanowires and subsequent percolation network formation via low-temperature nanowelding. The stretchable metal electrode from very long metal nanowires demonstrated high electrical conductivity (∼9 ohm sq−1) and mechanical compliance (strain > 460%) at the same time. This method is expected to overcome the performance limitation of the current stretchable electronics such as graphene, carbon nanotubes, and buckled nanoribbons. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Li-air(O2) and Li-S batteries have gained much attention recently and most relevant research has aimed to improve the electrochemical performance of air(O2) or sulfur cathode materials. However, many technical problems associated with the Li metal anode have yet to be overcome. This review mainly focuses on the electrochemical behaviors and technical issues related to metallic Li anode materials as well as other metallic anode materials such as alkali (Na) and alkaline earth (Mg) metals, including Zn and Al when these metal anodes were employed for various types of secondary batteries.

A major challenge for implantable medical systems is the inclusion or reliable delivery of electrical power. We use ultrasound to deliver mechanical energy through skin and liquids and demonstrate a thin implantable vibrating triboelectric generator able to effectively harvest it. The ultrasound can induce micrometer-scale displacement of a polymer thin membrane to generate electrical energy through contact electrification. We recharge a lithium-ion battery at a rate of 166 microcoulombs per second in water. The voltage and current generated ex vivo by ultrasound energy transfer reached 2.4 volts and 156 microamps under porcine tissue. These findings show that a capacitive triboelectric electret is the first technology able to compete with piezoelectricity to harvest ultrasound in vivo and to power medical implants.

The future electronics will be soft, flexible and even stretchable to be more human friendly in the form of wearable computers. However, conventional electronic materials are usually brittle. Recently, carbon based materials are intensively investigated as a good candidate for flexible electronics but with limited mechanical and electrical performances. Metal is still the best material for electronics with great electrical properties but with poor transparency and mechanical performance. Here we present a simple approach to develop a synthesis method for very long metallic nanowires and apply them as new types of high performance flexible and transparent metal conductors as an alternative to carbon nanotubes, graphene and short nanowire based flexible transparent conductors and indium tin oxide based brittle transparent conductors. We found that very long metallic nanowire network conductors combined with a low temperature laser nano-welding process enabled superior transparent flexible conductors with high transmittance and high electrical conductivity. Further, we demonstrated highly flexible metal conductor LED circuits and transparent touch panels. The highly flexible and transparent metal conductors can be mounted on any non-planar surfaces and applied for various opto-electronics and ultimately for future wearable electronics.

The vanadium redox flow battery, which was first suggested by Skyllas-Kazacos and co-workers in 1985, is an electrochemical storage system which allows energy to be stored in two solutions containing different redox couples.

Li-ion batteries have been employed successfully in various small electronic devices for the last two decades, and the types of applications are currently expanding to include electric vehicles (EVs), power tools, and large electric power storage units. In order to be implemented in these emerging markets, novel materials for negative and positive electrodes as well as electrolytes need to be developed to achieve high energy density, high power, and safe lithium rechargeable batteries. Here, the trends of the market and development of materials for each application are introduced, and some of next generation Li-ion batteries are discussed.

We demonstrate high-performance, flexible, transparent heaters based on large-scale graphene films synthesized by chemical vapor deposition on Cu foils. After multiple transfers and chemical doping processes, the graphene films show sheet resistance as low as ∼43 Ohm/sq with ∼89% optical transmittance, which are ideal as low-voltage transparent heaters. Time-dependent temperature profiles and heat distribution analyses show that the performance of graphene-based heaters is superior to that of conventional transparent heaters based on indium tin oxide. In addition, we confirmed that mechanical strain as high as ∼4% did not substantially affect heater performance. Therefore, graphene-based, flexible, transparent heaters are expected to find uses in a broad range of applications, including automobile defogging/deicing systems and heatable smart windows.

Recent growth of the insulated gate bipolar transistor (IGBT) module market has been driven largely by the increasing demand for an efficient way to control and distribute power in the field of renewable energy, hybrid/electric vehicles, and industrial equipment. For safety-critical and mission-critical applications, the reliability of IGBT modules is still a concern. Understanding the physics-of-failure of IGBT modules has been critical to the development of effective condition monitoring (CM) techniques as well as reliable prognostic methods. This review paper attempts to summarize past developments and recent advances in the area of CM and prognostics for IGBT modules. The improvement in material, fabrication, and structure is described. The CM techniques and prognostic methods proposed in the literature are presented. This paper concludes with recommendations for future research topics in the CM and prognostics areas.

Abstract The fabrication and design principles for using silver‐nanowire (AgNW) networks as transparent electrodes for flexible film heaters are described. For best practice, AgNWs are synthesized with a small diameter and network structures of the AgNW films are optimized, demonstrating a favorably low surface resistivity in transparent layouts with a high figure‐of‐merit value. To explore their potential in transparent electrodes, a transparent film heater is constructed based on uniformly interconnected AgNW networks, which yields an effective and rapid heating of the film at low input voltages. In addition, the AgNW‐based film heater is capable of accommodating a large amount of compressive or tensile strains in a completely reversible fashion, thereby yielding an excellent mechanical flexibility. The AgNW networks demonstrated here possess attractive features for both conventional and emerging applications of transparent flexible electrodes.

In a wireless power transfer (WPT) system via the magnetic resonant coupling, one of the most challenging design issues is to maintain a reasonable level of power transfer efficiency (PTE), even when the distance between the transmitter and the receiver changes. When the distance varies, the PTE drastically decreases due to the impedance mismatch between the resonator of the transmitter and that of the receiver. This paper presents a novel serial/parallel capacitor matrix in the transmitter, where the impedance can be automatically reconfigured to track the optimum impedance-matching point in the case of varying distances. The dynamic WPT matching system is enabled by changing the combination of serial and parallel capacitors in the capacitor matrix. An interesting observation in the proposed capacitor matrix is that the resonant frequency is not shifted, even with capacitor-matrix tuning. In order to quickly find the best capacitor combination that achieves maximum power transfer, a window-prediction-based search algorithm is also presented in this paper. The proposed resonance WPT system is implemented using a resonant frequency of 13.56 MHz, and the experimental results with 1W power transfer show that the transfer efficiency increases up to 88 % when the distance changes from 0 to 1.2 m.

Perovskite decomposition in detail Solar cells are subject to heating when operating in sunlight, and the organic components of hybrid perovskite solar cells, especially the commonly used methylammonium cation, can undergo thermal decomposition. Encapsulation can limit decomposition by bringing such reactions to equilibrium and can prevent exposure to damaging ambient moisture. Shi et al. examined several encapsulation schemes for perovskite films and devices by probing volatile products with gas chromatography–mass spectrometry (see the Perspective by Juarez-Perez and Haro). Pressure-tight polymer/glass stack encapsulation was effective in suppressing gas transfer and allowed solar cells containing methylammonium to pass harsh moisture and thermal cycling tests. Science , this issue p. eaba2412 ; see also p. 1309

The solvated-Na-ion intercalation in graphite is investigated in terms of stoichiometry, staging structure, and solvated ion configuration using combined experimental and theoretical studies.

Abstract With the aim of enhancing the field‐effect mobility by promoting surface‐mediated two‐dimensional molecular ordering in self‐aligned regioregular poly(3‐hexylthiophene) (P3HT) we have controlled the intermolecular interaction at the interface between P3HT and the insulator substrate by using self‐assembled monolayers (SAMs) functionalized with various groups (–NH 2 , –OH, and –CH 3 ). We have found that, depending on the properties of the substrate surface, the P3HT nanocrystals adopt two different orientations—parallel and perpendicular to the insulator substrate—which have field‐effect mobilities that differ by more than a factor of 4, and that are as high as 0.28 cm 2 V –1 s –1 . This surprising increase in field‐effect mobility arises in particular for the perpendicular orientation of the nanocrystals with respect to the insulator substrate. Further, the perpendicular orientation of P3HT nanocrystals can be explained by the following factors: the unshared electron pairs of the SAM end groups, the π–H interactions between the thienyl‐backbone bearing π‐systems and the H (hydrogen) atoms of the SAM end groups, and interdigitation between the alkyl chains of P3HT and the alkyl chains of the SAMs.

Rechargeable magnesium batteries have lately received great attention for large-scale energy storage systems due to their high volumetric capacities, low materials cost, and safe characteristic. However, the bivalency of Mg(2+) ions has made it challenging to find cathode materials operating at high voltages with decent (de)intercalation kinetics. In an effort to overcome this challenge, we adopt an unconventional approach of engaging crystal water in the layered structure of Birnessite MnO2 because the crystal water can effectively screen electrostatic interactions between Mg(2+) ions and the host anions. The crucial role of the crystal water was revealed by directly visualizing its presence and dynamic rearrangement using scanning transmission electron microscopy (STEM). Moreover, the importance of lowering desolvation energy penalty at the cathode-electrolyte interface was elucidated by working with water containing nonaqueous electrolytes. In aqueous electrolytes, the decreased interfacial energy penalty by hydration of Mg(2+) allows Birnessite MnO2 to achieve a large reversible capacity (231.1 mAh g(-1)) at high operating voltage (2.8 V vs Mg/Mg(2+)) with excellent cycle life (62.5% retention after 10000 cycles), unveiling the importance of effective charge shielding in the host and facile Mg(2+) ions transfer through the cathode's interface.

SiO2 is one of the most abundant materials on Earth. It is cost-effective and also environmentally benign when used as an energy material. Although SiO2 was inactive to Li, it was engineered to react directly by a simple process. It exhibited a strong potential as a promising anode for Li-ion batteries.

We introduce a facile approach to fabricate a metallic grid transparent conductor on a flexible substrate using selective laser sintering of metal nanoparticle ink. The metallic grid transparent conductors with high transmittance (>85%) and low sheet resistance (30 Ω/sq) are readily produced on glass and polymer substrates at large scale without any vacuum or high-temperature environment. Being a maskless direct writing method, the shape and the parameters of the grid can be easily changed by CAD data. The resultant metallic grid also showed a superior stability in terms of adhesion and bending. This transparent conductor is further applied to the touch screen panel, and it is confirmed that the final device operates firmly under continuous mechanical stress.

Abstract Considering the promising electrochemical performance of the recently reported pyrophosphate family in lithium ion batteries as well as the increasing importance of sodium ion batteries (SIBs) for emerging large‐scale applications, here, the crystal structure, electrochemical properties, and thermal stability of Na 2 FeP 2 O 7 , the first example ever reported in the pyrophosphate family for SIBs, are investigated. Na 2 FeP 2 O 7 maintains well‐defined channel structures (triclinic framework under the P1 space group) and exhibits a reversible capacity of ≈90 mAh g −1 with good cycling performance. Both quasi‐equilibrium measurements and first‐principles calculations consistently indicate that Na 2 FeP 2 O 7 undergoes two kinds of reactions over the entire voltage range of 2.0–4.5 V (vs Na/Na + ): a single‐phase reaction around 2.5 V and a series of two‐phase reactions in the voltage range of 3.0–3.25 V. Na 2 FeP 2 O 7 shows excellent thermal stability up to 500 °C, even in the partially desodiated state (NaFeP 2 O 7 ), which suggests its safe character, a property that is very critical for large‐scale battery applications.

Abstract The d-band center model of Hammer and Nørskov is widely used in understanding and predicting catalytic activity on transition metal (TM) surfaces. Here, we demonstrate that this model is inadequate for capturing the complete catalytic activity of the magnetically polarized TM surfaces and propose its generalization. We validate the generalized model through comparison of adsorption energies of the NH 3 molecule on the surfaces of 3d TMs (V, Cr, Mn, Fe, Co, Ni, Cu and Zn) determined with spin-polarized density functional theory (DFT)-based methods with the predictions of our model. Compared to the conventional d-band model, where the nature of the metal-adsorbate interaction is entirely determined through the energy and the occupation of the d-band center, we emphasize that for the surfaces with high spin polarization, the metal-adsorbate system can be stabilized through a competition of the spin-dependent metal-adsorbate interactions.

Single-crystalline triisopropylsilylethynyl pentacene (TIPS-PEN) microribbons (see figure) with well-defined facets and unprecedented electrical characteristics, such as a field-effect mobility as high as 1.4 cm2 V–1 s–1, are fabricated through the self-assembly of individual TIPS-PEN molecules as a result of solvophobic interactions in the solution phase adopting preferential well-ordered intermolecular π–π stacking along the ribbon axis. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2089/2007/c1259_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

In order to confirm reasons that deteriorate cathode performances, Ni-rich Li[Ni0.7Mn0.3]O2 is modified by lithium isopropoxide to artificially provide lithium excess environment by forming Li2O on the surface of active materials. X-ray diffraction patterns indicate that the lithium oxide coating does not affect structural change comparing to the bare material. Scanning electron microscopy and transmission electron microscopy data show the presence of coating layers on the surface of Li[Ni0.7Mn0.3]O2. Electrochemical tests demonstrate that the Li2O-coated Li[Ni0.7Mn0.3]O2 exhibits a greater irreversible capacity with a small capacity because of the presence of insulating layers composed of lithium compounds on the active materials since these layers delay facile Li+ diffusion. Also, the Li2O layer forms byproducts such as Li2CO3, LiOH, and LiF, as are proved by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. The presence of residual lithium tends to bond with hydrocarbons induced from decomposition of electrolytic salt during electrochemical reactions. And the reaction, accelerated by the decomposition of electrolytic salt that produces the byproducts, causes the formation of passive layers on the surface of active material. As a result, the new layers consequently impede diffusion of lithium ions that deteriorate electrochemical properties.