Flash-Induced High-Throughput Porous Graphene via Synergistic Photo-Effects for Electromagnetic Interference Shielding.

Porous 2D materials with high conductivity and large surface area have been proposed for potential electromagnetic interference (EMI) shielding materials in future mobility and wearable applications to prevent signal noise, transmission inaccuracy, system malfunction, and health hazards. Here, we report on the synthesis of lightweight and flexible flash-induced porous graphene (FPG) with excellent EMI shielding performance. The broad spectrum of pulsed flashlight induces photo-chemical and photo-thermal reactions in polyimide films, forming 5 × 10 cm2-size porous graphene with a hollow pillar structure in a few milliseconds. The resulting material demonstrated low density (0.0354 g cm-3) and outstanding absolute EMI shielding effectiveness of 1.12 × 105 dB cm2 g-1. The FPG was characterized via thorough material analyses, and its mechanical durability and flexibility were confirmed by a bending cycle test. Finally, the FPG was utilized in drone and wearable applications, showing effective EMI shielding performance for internal/external EMI in a drone radar system and reducing the specific absorption rate in the human body.

A 2D Ultrathin Nanopatterned Interlayer to Suppress Lithium Dendrite Growth in High-Energy Lithium-Metal Anodes.

A novel strategy for robust and ultrathin (<1 µm) multilayered protective structures to address uncontrolled Lithium (Li) dendrite growth at Li-metal battery anodes is reported. Synergetic interaction among Ag nanoparticles (Ag NPs), reduced graphene oxide (rGO) films, and self-assembled block-copolymer (BCP) layers enables effective suppression of dendritic Li growth. While Ag NP layer confines the growth of Li metal underneath the rGO layer, BCP layer facilitates the fast and uniformly distributed flux of Li-ion transport and mechanically supports the rGO layer. Notably, highly aligned nanochannels with ≈15 nm diameter and ≈600 nm length scale interpenetrating within the BCP layer offer reversible well-defined pathways for Li-ion transport. Dramatic stress relaxation with the multilayered structure is confirmed via structural simulation considering the mechanical stress induced by filamentary-growth of Li metal. Li-metal anodes modified with the protective layer well-maintain stable reaction interfaces with limited solid-electrolyte interphase formation, yielding outstanding cycling stability and enhanced rate capability, as demonstrated by the full-cells paired with high-loading of LiFePO4 cathodes. The idealized design of multilayer protective layer provides significant insight for advanced Li-metal anodes.

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.

Strategically Controlled Flash Irradiation on Silicon Anode for Enhancing Cycling Stability and Rate Capability toward High-Performance Lithium-Ion Batteries.

Si has attracted considerable interest as a promising anode material for next-generation Li-ion batteries owing to its outstanding specific capacity. However, the commercialization of Si anodes has been consistently limited by severe instabilities originating from their significant volume change (approximately 300%) during the charge-discharge process. Herein, we introduce an ultrafast processing strategy of controlled multi-pulse flash irradiation for stabilizing the Si anode by modifying its physical properties in a spatially stratified manner. We first provide a comprehensive characterization of the interactions between the anode materials and the flash irradiation, such as the condensation and carbonization of binders, sintering, and surface oxidation of the Si particles under various irradiation conditions (e.g., flash intensity and irradiation period). Then, we suggest an effective route for achieving superior physical properties for Si anodes, such as robust mechanical stability, high electrical conductivity, and fast electrolyte absorption, via precise adjustment of the flash irradiation. Finally, we demonstrate flash-irradiated Si anodes that exhibit improved cycling stability and rate capability without requiring costly synthetic functional binders or delicately designed nanomaterials. This work proposes a cost-effective technique for enhancing the performance of battery electrodes by substituting conventional long-term thermal treatment with ultrafast flash irradiation.

Control of thermal deformation with photonic sintering of ultrathin nanowire transparent electrodes.

Development of electronic devices on ultrathin flexible plastic substrates is of great value in terms of portability, cost reduction, and mechanical flexibility. However, because thin plastic substrates with low heat capacity can be more easily damaged by thermal energy, their use is limited. Highly flexible nanowire (NW) transparent conductive electrodes on ultrathin (∼10 µm) low cost polyethylene terephthalate (PET) substrates are fabricated. The control of intense pulsed light (IPL) irradiation process parameters to induce NW welding for maximum conductivity and minimal thermal damage of the PET substrate is explored. For this purpose, trends in temperature variation of NW thin films irradiated by IPL under various operating conditions are numerically analyzed using commercial software. Simulations indicate that irradiating light operated at a higher voltage and for a shorter time, and use of multiple pulses of low frequency can reduce thermal deformation of the PET substrate. Furthermore, we experimentally confirm that NW transparent electrodes can be successfully fabricated with less thermal deformation of the ultrathin plastic substrate when light is irradiated under well-controlled conditions derived from the simulation. The highly flexible NW transparent conducting electrode exhibits excellent mechanical flexibility to withstand severe deformation and can be successfully implemented in flexible organic light-emitting diodes (OLEDs).

Flash-Induced Stretchable Cu Conductor via Multiscale-Interfacial Couplings.

Herein, a novel stretchable Cu conductor with excellent conductivity and stretchability is reported via the flash-induced multiscale tuning of Cu and an elastomer interface. Microscale randomly wrinkled Cu (amplitude of ≈5 µm and wavelength of ≈45 µm) is formed on a polymer substrate through a single pulse of a millisecond flash light, enabling the elongation of Cu to exceed 20% regardless of the stretching direction. The nanoscale interlocked interface between the Cu nanoparticles (NPs) and the elastomer increases the adhesion force of Cu, which contributes to a significant improvement of the Cu stability and stretchability under harsh yielding stress. Simultaneously, the flash-induced photoreduction of CuO NPs and subsequent Cu NP welding lead to outstanding conductivity (≈37 kS cm-1) of the buckled elastic electrode. The 3D structure of randomly wrinkled Cu is modeled by finite element analysis simulations to show that the flash-activated stretchable Cu conductors can endure strain over 20% in all directions. Finally, the wrinkled Cu is utilized for wireless near-field communication on the skin of human wrist.

Self-Generated Nanoporous Silver Framework for High-Performance Iron Oxide Pseudocapacitor Anodes.

The rapid development of electric vehicles is increasing the demand for next-generation fast-charging energy storage devices with a high capacity and long-term stability. Metal oxide/hydroxide pseudocapacitors are the most promising technology because they show a theoretical capacitance that is 10-100 times higher than that of conventional supercapacitors and rate capability and long-term stability that are much higher than those of Li-ion batteries. However, the poor electrical conductivity of metal oxides/hydroxides is a serious obstacle for achieving the theoretical pseudocapacitor performance. Here, a nanoporous silver (np-Ag) structure with a tunable pore size and ligament is developed using a new silver halide electroreduction process. The structural characteristics of np-Ag (e.g., large specific surface area, electric conductivity, and porosity) are desirable for metal oxide-based pseudocapacitors. This work demonstrates an ultra-high-capacity, fast-charging, and long-term cycling pseudocapacitor anode via the development of an np-Ag framework and deposition of a thin layer of Fe2O3 on its surface (np-Ag@Fe2O3). The np-Ag@Fe2O3 anode shows a capacitance of ∼608 F g-1 at 10 A g-1, and ∼84.9% of the capacitance is retained after 6000 charge-discharge cycles. This stable and high-capacity anode, which can be charged within a few tens of seconds, is a promising candidate for next-generation energy storage devices.