In Situ Mesopore Formation in SiOx Nanoparticles by Chemically Reinforced Heterointerface and Use of Chemical Prelithiation for Highly Reversible Lithium-Ion Battery Anode.

SiOx is a promising next-generation anode material for lithium-ion batteries. However, its commercial adoption faces challenges such as low electrical conductivity, large volume expansion during cycling, and low initial Coulombic efficiency. Herein, to overcome these limitations, an eco-friendly in situ methodology for synthesizing carbon-containing mesoporous SiOx nanoparticles wrapped in another carbon layers is developed. The chemical reactions of vinyl-terminated silanes are designed to be confined inside the cationic surfactant-derived emulsion droplets. The polyvinylpyrrolidone-based chemical functionalization of organically modified SiO2 nanoparticles leads to excellent dispersion stability and allows for intact hybridization with graphene oxide sheets. The formation of a chemically reinforced heterointerface enables the spontaneous generation of mesopores inside the thermally reduced SiOx nanoparticles. The resulting mesoporous SiOx -based nanocomposite anodes exhibit superior cycling stability (≈100% after 500 cycles at 0.5 A g-1 ) and rate capability (554 mAh g-1 at 2 A g-1 ), elucidating characteristic synergetic effects in mesoporous SiOx -based nanocomposite anodes. The practical commercialization potential with a significant enhancement in initial Coulombic efficiency through a chemical prelithiation reaction is also presented. The full cell employing the prelithiated anode demonstrated more than 2 times higher Coulombic efficiency and discharge capacity compared to the full cell with a pristine anode.

Green and Facile Synthesis of Hybrid Composites with Ultralow Dielectric Properties from Water-Soluble Polyimide and Dual-Porous Silica Nanoparticles.

Here, we proposed an eco-friendly synthetic method for synthesizing hybrid composites with ultralow dielectric properties at high frequencies up to 28 GHz for true 5G communication from aqueous aromatic polyimide (PI) polymers and dual-porous silica nanoparticles (DPS). The "one-step" water-based emulsion template method was used to synthesize the macroporous silica nanoparticles (MPS). A substantially negative ζ potential was produced along the surface of MPS by the poly(vinylpyrrolidone)-based chemical functionalization, enabling excellent aqueous dispersion stability. The water-soluble poly(amic acid) (PAA), as a precursor to PI, was also "one-step" polymerized in an aqueous solution. The MPS were dispersed in a water-soluble PAA matrix to create the hybrid composite films using an entirely water-based approach. The compatibility between the PAA matrix and MPS was elucidated by investigating relatively diverse end-terminated PAAs (with either amine or carboxyl group). It was also discovered that, during a thermally activated imidization reaction, the MPS are in situ converted into the DPS with macro- and microporous structures (with a surface area of 1522.4 m2/g). The thermal, dielectric, mechanical, and morphological characteristics of each composite film were examined, while the amount of DPS in the PI matrix varied from 1 to 20 wt %. With the addition of 5 wt % DPS as an optimum condition, it showed ultralow dielectric properties, with the Dk and Df being 1.615 and 0.003 at a frequency of 28 GHz, respectively, and compatible mechanical properties, with the tensile strength and elastic modulus being 78.2 MPa and 0.32 GPa, respectively. These results can comprehensively satisfy various physical properties required as a substrate material for 5G communication devices.

3D Flower-like Tin Monosulfide/Carbon Nanocomposite Anodes for Sodium-Ion Batteries.

The nanostructured tin monosulfide/carbon composites were synthesized by a simple wet chemical synthesis approach. It was revealed that the 3D flower-like tin monosulfide nanoparticles are usable as an active anode material for sodium-ion batteries, exhibiting a specific capacity of 480.4 mAh/g. The 3D flower-like tin monosulfide nanoparticles were wrapped with reduced graphene oxide sheets by a solvothermal heterogeneous synthetic method. By incorporating the reduced graphene oxide sheets as a mechanically flexible and electrically conductive additive, a specific capacity of 633.2 mAh/g was obtained from tin monosulfide/carbon nanocomposite anodes, providing an excellent rate capability even at a high current density condition of 5000 mA/g.

Printable Self-Activated Liquid Metal Stretchable Conductors from Polyvinylpyrrolidone-Functionalized Eutectic Gallium Indium Composites.

Stretchable electronic circuits are critical in a variety of next-generation electronics applications, including soft robots, wearable technologies, and biomedical applications. To date, printable composite conductors comprising various types of conductive fillers have been suggested to achieve high electrical conductance and excellent stretchability. Among them, liquid metal particles have been considered as a viable candidate filler that can meet the necessary prerequisites. However, a mechanical activation process is needed to generate interconnected liquid channels inside elastomeric polymers. In this study, we have developed a chemical strategy of surface-functionalizing liquid metal particles to eliminate the necessity of additional mechanical activation processes. We found that the characteristic conformations of the polyvinylpyrrolidone surrounding eutectic gallium indium particles are highly dependent on the molecular weight of polyvinylpyrrolidone. By virtue of the specific chemical roles of polyvinylpyrrolidone, the as-printed composite layers are highly conductive and stretchable, exhibiting an electrical conductivity approaching 8372 S/cm at 100% strain and an invariant resistance change of 0.92 even at 75% strain after a 60,000 cycle test. The results demonstrate that the self-activated liquid metal-based composite conductors are applicable to traditional stretchable electronics, healable stretchable electronics, and shape-morphable applications.

Flashlight-Induced Strong Self-Adhesive Surface on a Nanowire-Impregnated Transparent Conductive Film.

The flashlight annealing process has been widely used in the field of flexible and printed electronics because it can instantly induce chemical and structural modifications over a large area on an electronic functional layer in a subsecond time range. In this study, for the first time, we explored a straightforward method to develop strong self-adhesion on a metal nanowire-based flexible and transparent conductive film via flashlight irradiation. Nanowire interlocking, for strong mechanical bonding at the interface between the nanowires and polyamide film, was achieved by simple hot pressing. Then, by irradiating the nanowire-impregnated film with a flashlight, several events such as interdiffusion and melting of surface polymers could be induced along with morphological changes leading to an increase in the film surface area. As a result, the surface of the fabricated film exhibited strong interfacial interactions while forming intimate contact with the heterogeneous surfaces of other objects, thereby becoming strongly self-adhesive. This readily achievable, self-attachable, flexible, and transparent electrode allowed the self-interconnection of a light-emitting diode chip, and it was also compatible for various applications, such as defogging windows and transparent organic light-emitting diodes.

Three-Dimensional Multistack-Printed, Self-Powered Flexible Pressure Sensor Arrays: Piezoelectric Composites with Chemically Anchored Heterogeneous Interfaces.

Recently, the development of pressure sensor devices composed of mechanically flexible materials has gained a tremendous attention for emerging wearable electronics applications. Compared with various sensing materials, piezoelectric composite materials provide a characteristic advantage of enabling energy unit-free integration of sensor compartments. In this study, we develop a new chemical method of synthesizing highly functioning piezoelectric composite materials with electrostatically reinforced heterogeneous interfaces to improve the voltage output signal in all-printed sensor arrays. The surfaces of piezoelectric oxide nanoparticles are decorated subsequently with a cationic polyelectrolyte, polyethyleneimine, and a tri-block copolymer, styrene-ethylene/butylene-styrene grafted with maleic anhydride. To elucidate the factors determining the performance of pressure sensor devices, both the electrical properties and piezoelectric characteristics are investigated comprehensively for various compositional composite materials prepared from chemical and physical rubbers. The resulting device exhibits a sensitivity of 0.28 V·kPa-1 with a linear increment of output voltage in a pressure range up to 30 kPa. It is also demonstrated that the all-printed sensor array is fabricated successfully by a multistack-printing process of conductive, insulating, and piezoelectric composite materials in an additive manufacturing fashion.

Lubricant-Added Conductive Composite for Direct Writing of a Stretchable Electrode.

Stretchable electrodes, which are essential components of next-generation electronic devices, should be highly conductive under multiaxial tensile strain, durable under repetitive stretching, and patternable for integrating stretchable devices. Herein, a lubricant-added stretchable conductive composite of a polydimethylsiloxane-based elastomer containing silver flakes is reported. The added lubricant minimizes changes in conductivity during stretching and maximizes elastic durability by reducing friction. The conductivity varies from 1933.3 S·cm-1 at 0% strain to 307.5 S·cm-1 at 300% uniaxial stretching and 1264.1 S·cm-1 at 50% biaxial stretching. Furthermore, the composite exhibits high durability, even after 1000 cycles of stretching at 200%, and the conductive composite paste can be applied to fine-linewidth direct writing.

Printable Thick Copper Conductors from Optically Modulated Multidimensional Particle Mixtures.

Printing techniques that enable the formation of arbitrarily designed architectures have been implemented in various research fields owing to their characteristic advantages in processing over other techniques. In particular, low-cost, printable conductors are of paramount importance in the production of highly functioning printed electronics. Among various candidates, copper (Cu) particle-based printable fluid has been regarded as the most promising constituent material in conjunction with the use of the flash-light-sintering (FLS) process in air. In this study, we synthesized surface-oxidation-suppressed Cu nanoparticles, sub-micronparticles, and flakes to regulate the optical absorption characteristics in FLS-processed, Cu-based printed conductors. Our results revealed clearly that the critical issues in FLS-processed conductors, namely, undesirable crack formation and a limitation of thickness, are resolved by adjusting the optical behaviors of particulate layers by variation of the composition of multidimensional mixture particles. It is suggested that crack-free, 13.2 µm thick printed Cu conductors can be generated with a resistivity of 11.4 µΩ cm by printing and FLS processes in air. The proposed alternative approach is demonstrated with electrical circuits comprising electrodes and interconnections.

Three-Dimensionally Printed Stretchable Conductors from Surfactant-Mediated Composite Pastes.

A stretchable conductor is a critical prerequisite to achieve various forms of stretchable electronics. In particular, directly printable stretchable conductors have gathered considerable attention with recent growing interest in a variety of large-area, deformable electronics. In this study, we have developed a chemical pathway of incorporating a surfactant with a moderate hydrophilic-lipophilic balance in formulating composite pastes for printed stretchable conductors, with a possibility of a vertically stackable, three-dimensional printing process. We demonstrate that the addition of a nonionic surfactant, sorbitane monooleate (commonly called SPAN 80) in Ag flake-based composite pastes, allows a critical reduction in resistance variation under an external strain. The four-layer stacked, surfactant-added composite conductors show a resistance variation of merely 1.6 at a strain of 0.6 and excellent cycling durability over 1000 cycles. The effectiveness of the methods suggested in this study is demonstrated with basic light-emitting diode circuits and the thermal heating characteristics of stretchable conductors.

Three-dimensionally printed pressure sensor arrays from hysteresis-less stretchable piezoresistive composites.

In this study, we formulate three-dimensionally (3D) printable composite pastes employing electrostatically assembled-hybrid carbon and a polystyrene-polyisoprene-polystyrene tri-block copolymer elastomer for the fabrication of multi-stack printed piezoresistive pressure sensor arrays. To address a critical drawback of piezoresistive composite materials, we have developed a previously unrecognized strategy of incorporating a non-ionic amphiphilic surfactant, sorbitan trioleate, into composite materials. It is revealed that the surfactant with an appropriate amphiphilic property, represented by the hydrophilic-lipophilic balance (HLB) index of 1.8, allows for a reversible piezoresistive characteristic under a wide pressure range up to 30 kPa as well as a significant reduction of elastomer viscoelastic behavior. The 3D-printed pressure sensor arrays exhibit a sensitivity of 0.31 kPa-1 in a linear trend, and it is demonstrated successfully that the position-addressable array device is capable of spatially detecting objects up to a pressure level of 22.1 kPa.

High-Power Aqueous Zinc-Ion Batteries for Customized Electronic Devices.

Wireless electronic devices require small, rechargeable batteries that can be rapidly designed and fabricated in customized form factors for shape conformable integration. Here, we demonstrate an integrated design and manufacturing method for aqueous zinc-ion batteries composed of polyaniline (PANI)-coated carbon fiber (PANI/CF) cathodes, laser micromachined zinc (Zn) anodes, and porous separators that are packaged within three-dimensional printed geometries, including rectangular, cylindrical, H-, and ring-shapes. The PANI/CF cathode possesses high surface area and conductivity giving rise to high rate (∼600 C) performance. Due to outstanding stability of Zn-PANI batteries against oxygen and moisture, they exhibit long cycling stability in an aqueous electrolyte solution. As exemplar, we demonstrated rechargeable battery packs with tunable voltage and capacity using stacked electrodes that are integrated with electronic components in customized wearable devices.

Highly durable Cu-based electrodes from a printable nanoparticle mixture ink: flash-light-sintered, kinetically-controlled microstructure.

Recently, printable nanomaterials have drawn tremendous attention for low-cost, large-area electronics applications. In particular, metallic nanoparticles that can facilitate the formation of highly functioning electrodes are indispensable constituent nanomaterials. In this paper, we propose printable mixed inks comprising multicomponent ingredients of Cu, Ni and Cu/Cu10Sn3 core/shell nanoparticles. It is clearly revealed that a characteristic morphology appropriate to highly conductive and durable Cu-based electrodes can be derived easily in a timescale of about 1 ms through an instantaneous flash-light-sintering process, resulting in a resistivity of 49 µΩ cm and normalized resistance variation of around 1 (after 28 days under a harsh environment of 85 °C temperature and 85% humidity). In addition, it is demonstrated that highly functioning electrodes can be formed on thermally vulnerable polyethylene terephthalate (PET) substrates by incorporating an ultrathin optical/thermal plasmonic barrier layer.

Correction: 3D polymer objects with electronic components interconnected via conformally printed electrodes.

Correction for '3D polymer objects with electronic components interconnected via conformally printed electrodes' by Yejin Jo, et al., Nanoscale, 2017, 9, 14798-14803.

Room-Temperature, Ambient-Pressure Chemical Synthesis of Amine-Functionalized Hierarchical Carbon-Sulfur Composites for Lithium-Sulfur Battery Cathodes.

Recently, the achievement of newly designed carbon-sulfur composite materials has attracted a tremendous amount of attention as high-performance cathode materials for lithium-sulfur batteries. To date, sulfur materials have been generally synthesized by a sublimation technique in sealed containers. This is a well-developed technique for the synthesizing of well-ordered sulfur materials, but it is limited when used to scale up synthetic procedures for practical applications. In this study, we suggest an easily scalable, room-temperature/ambient-pressure chemical pathway for the synthesis of highly functioning cathode materials using electrostatically assembled, amine-terminated carbon materials. It is demonstrated that stable cycling performance outcomes are achievable with a capacity of 730 mAhg-1 at a current density of 1 C with good cycling stability by a virtue of the characteristic chemical/physical properties (a high conductivity for efficient charge conduction and the presence of a number of amine groups that can interact with sulfur atoms during electrochemical reactions) of composite materials. The critical roles of conductive carbon moieties and amine functional groups inside composite materials are clarified with combinatorial analyses by X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy.

3D-printed origami electronics using percolative conductors.

Recently, three-dimensional (3D) printing has garnered tremendous amounts of attention in various applications. In this study, we suggest a facile means of creating 3D-printed foldable electrodes on paper via the direct printing of composite pastes consisting of conductive fillers and a thermoplastic elastomer. The 3D-printability of the prepared composite pastes is investigated depending on the rheological properties. It is revealed that the composite paste with a high storage modulus would enable the formation of highly conductive features with a resistance of 0.4 Ω cm-1 on three-dimensional paper structures. The mechanical bending/folding stability levels of the printed electrodes are evaluated to judge the possibility of realizing 3D-printed origami electronics. The resistance is changed slightly with a normalized resistance value of 2.3, when the printed electrodes are folded with a folding angle of 150°. It is demonstrated that the 3D-printed composite electrodes are applicable to various origami electronics, including electrical circuits, strain sensors and electrochemical sensors.

Enhanced Oxidation-Resistant Cu@Ni Core-Shell Nanoparticles for Printed Flexible Electrodes.

In this work, the fabrication and application of highly conductive, robust, flexible, and oxidation-resistant Cu-Ni core-shell nanoparticle (NP)-based electrodes have been reported. Cu@Ni core-shell NPs with a tunable Ni shell thickness were synthesized by varying the Cu/Ni molar ratios in the precursor solution. Through continuous spray coating and flash photonic sintering without an inert atmosphere, large-area Cu@Ni NP-based conductors were fabricated on various polymer substrates. These NP-based electrodes demonstrate a low sheet resistance of 1.3 Ω sq-1 under an optical energy dose of 1.5 J cm-2. In addition, they exhibit highly stable sheet resistances (ΔR/R0 < 1) even after 30 days of aging at 85 °C and 85% relative humidity. Further, a flexible heater fabricated from the Cu@Ni film is demonstrated, which shows uniform heat distribution and stable temperature compared to those of a pure Cu film.

Ultrathin Plasmonic Optical/Thermal Barrier: Flashlight-Sintered Copper Electrodes Compatible with Polyethylene Terephthalate Plastic Substrates.

In recent years, highly conductive, printable electrodes have received tremendous attention in various research fields as the most important constituent components for large-area, low-cost electronics. In terms of an indispensable sintering process for generating electrodes from printable metallic nanomaterials, a flashlight-based sintering technique has been regarded as a viable approach for continuous roll-to-roll processes. In this paper, we report cost-effective, printable Cu electrodes that can be applied to vulnerable polyethylene terephthalate (PET) substrates, by incorporating a heretofore-unrecognized ultrathin plasmonic thermal/optical barrier, which is composed of a 30 nm thick Ag nanoparticle (NP) layer. The different plasmonic behaviors during a flashlight-sintering process are investigated for both Ag and Cu NPs, based on a combined interpretation of the experimental results and theoretical calculations. It is demonstrated that by a continuous printing process and a continuous flashlight-sintering process, the Cu electrodes are formed successfully on large PET substrates, with a sheet resistance of 0.24 Ω/sq and a resistivity of 22.6 µΩ·cm.

3D polymer objects with electronic components interconnected via conformally printed electrodes.

We report the fabrication of 3D polymer objects that contain electrical components interconnected by conductive silver/carbon nanotube inks printed conformally onto their surfaces and through vertical vias. Electrical components are placed within internal cavities and recessed surfaces of polymer objects produced by stereolithography. Conformally printed electrodes that interconnect each electrical component exhibit a conductivity of ∼2 × 104 S cm-1 upon annealing at temperatures below 100 °C. Multiple 3D objects were created to demonstrate this hybrid additive manufacturing approach, including those with an embedded circuit operated by an air-suspended switch and a 3D circuit board composed of microcontroller unit, resistor, battery, light-emitting diode and sensor.

Understanding the Critical Role of the Ag Nanophase in Boosting the Initial Reversibility of Transition Metal Oxide Anodes for Lithium-Ion Batteries.

The initial reversible capacity, a critical impediment in transition metal oxide-based anodes, is augmented in conversion-reaction-involved CoO anodes for lithium-ion batteries, by incorporating a chemically synthesized Ag nanophase. With an increase in the added amount of Ag nanophase from 5 to 15 wt %, the initial capacity loss decreases linearly up to 31.7%. The Ag nanophase maintains its pristine metallic nature without undergoing phase transformations, even during repeated vigorous electrochemical reactions of the active CoO phase. Complementary ex situ chemical/physical analyses suggest that the Ag nanophase promotes the catalytic generation of reversible gel-like/polymeric films wherein lithium ions are stored capacitively in the low-voltage region below 0.7 V during discharging. These scientific findings would provide a heretofore unrecognized pathway to resolving a major issue associated with the critical irreversibility in conversion-type transition metal oxide anodes.

3D printable composite dough for stretchable, ultrasensitive and body-patchable strain sensors.

The recent development of strain sensor devices which can actively monitor human body motion has attracted tremendous attention, for application in various wearable electronics and human-machine interfaces. In this study, as materials for strain sensor devices, we exploit the low-cost, carbon-based, 3-dimensional (3D) printable composite dough. The dough is prepared via a chemical method based on the formation of electrostatic assemblies between 1-dimensional, amine-functionalized, multi-walled carbon nanotubes and 2-dimensional graphene oxides. The resulting composite dough has an extremely high storage modulus, which allows a vertically-stackable, 3D printing process for fabricating strain sensor devices on various dense, porous and structured substrates. The device performance parameters, including gauge factor, hysteresis, linearity, and overshooting behavior are found to be adjustable by controlling the printing process parameters. The fabricated strain sensor devices demonstrate the ability to distinguish actual human body motions. A high gauge factor of over 70 as well as other excellent device performance parameters are achievable for the printed sensor devices, and even small strains, below 1%, are also detectable by the fabricated sensor devices.