Advanced Additive Manufacturing of Structurally-Colored Architectures.

Direct ink writing (DIW) stands out as a facile additive manufacturing method, minimizing material waste. Nonetheless, developing homogeneous Bingham inks with high yield stress and swift liquid-to-solid transitions for versatile 3D printing remains a challenge. In this study, high-performance Bingham inks are formulated by destabilizing silica particle suspensions in acrylate-based resin. A colloidal network forms in the shear-free state through interparticle attraction, achieved by disrupting the solvation layer of large resin molecules using polar molecules. The network is highly dense, with evenly distributed linkage strength as monodisperse particles undergo gelation at an ultra-high fraction. Crucially, the strength is calibrated to ensure a sufficiently large yield stress, while still allowing the network to reversibly melt under shear flow. The inks immediately undergo a liquid-to-solid transition upon discharge, while maintaining fluidity without nozzle clogging. The dense colloidal networks develop structural colors due to the short-range order. This enables the rapid and sophisticated drawing of structurally-colored 3D structures, relying solely on rheological properties. Moreover, the printed composite structures exhibit high mechanical stability due to the presence of the colloidal network, which expands the range of potential applications.

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.

Direct writing of customized structural-color graphics with colloidal photonic inks.

Colloidal crystals and glasses have been designed to develop structural colors that are tunable, iridescent, nonfading, and nontoxic. However, the low printability and poor printing quality have restricted their uses. Here, we report the direct writing of structural-color graphics with high brightness and saturation using colloidal inks. The inks are prepared by dispersing silica particles in acrylate-based resins, where the volume fraction is optimized to simultaneously provide pronounced coloration and satisfactory printing rheology. With the inks, any macroscopic design of lines and faces can be directly written on various substrates, where the microscopic colloidal arrangement is set to be either crystalline or amorphous depending on the resin viscosity to control the iridescence of the colors. In addition, the high mechanical stability and controlled modulus enable the graphics to be surface-transferred, origami-folded, or elastically stretched. This direct-writing approach provides unprecedented levels of controllability and versatility for pragmatic uses of structural colors.

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.

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.

Polyethylenimine-Mediated Electrostatic Assembly of MnO2 Nanorods on Graphene Oxides for Use as Anodes in Lithium-Ion Batteries.

In recent years, the development of electrochemically active materials with excellent lithium storage capacity has attracted tremendous attention for application in high-performance lithium-ion batteries. MnO2-based composite materials have been recognized as one of promising candidates owing to their high theoretical capacity and cost-effectiveness. In this study, a previously unrecognized chemical method is proposed to induce intra-stacked assembly from MnO2 nanorods and graphene oxide (GO), which is incorporated as an electrically conductive medium and a structural template, through polyethylenimine (PEI)-derived electrostatic modulation between both constituent materials. It is revealed that PEI, a cationic polyelectrolyte, is capable of effectively forming hierarchical, two-dimensional MnO2-RGO composites, enabling highly reversible capacities of 880, 770, 630, and 460 mA·h/g at current densities of 0.1, 1, 3, and 5 A/g, respectively. The role of PEI in electrostatically assembled composite materials is clarified through electrochemical impedance spectroscopy-based comparative analysis.

3D intra-stacked CoO/carbon nanocomposites welded by Ag nanoparticles for high-capacity, reversible lithium storage.

A wet-chemical, facile strategy is proposed for forming three-dimensional intra-structured nanocomposites to facilitate the development of high performance anodes for lithium ion batteries. The nanocomposites are composed of cobalt oxide nanoparticles, reduced graphene oxides, and Ag nanoparticles, and all the constituent materials are incorporated homogenously in a layer-by-layer structured geometry by a simple sono-chemical hybridizing process in a single, one-pot batch. Herein, it is revealed that the homogenously intra-stacked oxide, carbon, and metallic phases play critical roles in determining electrochemical performance (i.e. high capacity, rate capability, and cycling stability) of nanocomposite-based anodes, owing to the characteristic chemical/physical nature of constituent materials welded by partial melting of the metallic nanoparticles. In particular, by virtue of a characteristic role of a nano-Ag phase in suppressing the irreversible capacity, a critical drawback for metal oxide-based anodes, excellent capacities are demonstrated (983 and 770 mA h g(-1) at current densities of 100 and 2000 mA g(-1), respectively).

Superior lithium storage performance using sequentially stacked MnO2/reduced graphene oxide composite electrodes.

Hybrid nanostructures based on graphene and metal oxides hold great potential for use in high-performance electrode materials for next-generation lithium-ion batteries. Herein, a new strategy to fabricate sequentially stacked α-MnO2 /reduced graphene oxide composites driven by surface-charge-induced mutual electrostatic interactions is proposed. The resultant composite anode exhibits an excellent reversible charge/discharge capacity as high as 1100 mA h g(-1) without any traceable capacity fading, even after 100 cycles, which leads to a high rate capability electrode performance for lithium ion batteries. Thus, the proposed synthetic procedures guarantee a synergistic effect of multidimensional nanoscale media between one (metal oxide nanowire) and two dimensions (graphene sheet) for superior energy-storage electrodes.

3D-stacked carbon composites employing networked electrical intra-pathways for direct-printable, extremely stretchable conductors.

The newly designed materials for stretchable conductors meeting the demands for both electrical and mechanical stability upon morphological elongation have recently been of paramount interest in the applications of stretchable, wearable electronics. To date, carbon nanotube-elastomeric polymer mixtures have been mainly developed; however, the method of preparing such CNT-polymer mixtures as stretchable conductors has been limited to an ionic liquid-mediated approach. In this study, we suggest a simple wet-chemical method for producing newly designed, three-dimensionally stacked carbon composite materials that facilitate the stable morphological elongation up to a strain of 300% with normalized conductivity variation of only 0.34 under a strain of 300%. Through a comparative study with other control samples, it is demonstrated that the intraconnected electrical pathways in hierarchically structured composite materials enable the generation of highly stretchable conductors. Their direct patternability is also evaluated by printing on demand using a programmable disperser without the use of prepatterned masks.