Showing papers by "Jang Wook Choi published in 2010"

Stretchable, Porous, and Conductive Energy Textiles

Abstract: Recently there is strong interest in lightweight, flexible, and wearable electronics to meet the technological demands of modern society. Integrated energy storage devices of this type are a key area that is still significantly underdeveloped. Here, we describe wearable power devices using everyday textiles as the platform. With an extremely simple “dipping and drying” process using single-walled carbon nanotube (SWNT) ink, we produced highly conductive textiles with conductivity of 125 S cm−1 and sheet resistance less than 1 Ω/sq. Such conductive textiles show outstanding flexibility and stretchability and demonstrate strong adhesion between the SWNTs and the textiles of interest. Supercapacitors made from these conductive textiles show high areal capacitance, up to 0.48F/cm2, and high specific energy. We demonstrate the loading of pseudocapacitor materials into these conductive textiles that leads to a 24-fold increase of the areal capacitance of the device. These highly conductive textiles can provide ...

Light-Weight Free-Standing Carbon Nanotube-Silicon Films for Anodes of Lithium Ion Batteries

Abstract: Silicon is an attractive alloy-type anode material because of its highest known capacity (4200 mAh/g). However, lithium insertion into and extraction from silicon are accompanied by a huge volume change, upto300%,whichinducesastrongstrainonsiliconandcausespulverizationandrapidcapacityfadingduetothe loss of the electrical contact between part of silicon and current collector. Si nanostructures such as nanowires, which are chemically and electrically bonded to the current collector, can overcome the pulverization problem, however, the heavy metal current collectors in these systems are larger in weight than Si active material. Herein we report a novel anode structure free of heavy metal current collectors by integrating aflexible, conductive carbon nanotube (CNT) network into a Si anode. The compositefilm is free-standing and has a structure similar to the steel bar reinforced concrete, where the infiltrated CNT network functions as both mechanical support and electrical conductor and Si as a high capacity anode material for Li-ion battery. Such free-standing film has a low sheet resistance of30 Ohm/sq. It shows a high specific charge storage capacity (2000 mAh/g) and a good cycling life, superior to pure sputtered-on siliconfilms with similar thicknesses. Scanning electron micrographs show that Si is still connected by the CNT network even when small breaking or cracks appear in the film after cycling. Thefilm can also "ripple up" to release the strain of a large volume change during lithium intercalation. The conductive compositefilm can function as both anode active material and current collector. It offers10 times improvement in specific capacity compared with widely used graphite/copper anode sheets.

Stepwise Nanopore Evolution in One-Dimensional Nanostructures

Abstract: We report that established simple lithium (Li) ion battery cycles can be used to produce nanopores inside various useful one-dimensional (1D) nanostructures such as zinc oxide, silicon, and silver nanowires. Moreover, porosities of these 1D nanomaterials can be controlled in a stepwise manner by the number of Li-battery cycles. Subsequent pore characterization at the end of each cycle allows us to obtain detailed snapshots of the distinct pore evolution properties in each material due to their different atomic diffusion rates and types of chemical bonds. Also, this stepwise characterization led us to the first observation of pore size increases during cycling, which can be interpreted as a similar phenomenon to Ostwald ripening in analogous nanoparticle cases. Finally, we take advantage of the unique combination of nanoporosity and 1D materials and demonstrate nanoporous silicon nanowires (poSiNWs) as excellent supercapacitor (SC) electrodes in high power operations compared to existing devices with activ...

Fast and Scalable Printing of Large Area Monolayer Nanoparticles for Nanotexturing Applications

Abstract: Recently, there have been several studies demonstrating that highly ordered nanoscale texturing can dramatically increase performance of applications such as light absorption in thin-film solar cells. However, those methods used to make the nanostructures are not compatible with large-scale fabrication. Here we demonstrate that a technique currently used in roll-to-roll processing to deposit uniform thin films from solution, a wire-wound rod coating method, can be adapted to deposit close-packed monolayers or multilayers of silica nanoparticles on a variety of rigid and flexible substrates. Amorphous silicon thin films deposited on these nanoparticle monolayers exhibit 42% higher absorption over the integrated AM 1.5 spectrum than the planar controls. This simple assembly technique can be used to improve solar cells, fuel cells, light emitting diodes and other devices where ordered nanoscale texturing is critical for optimal performance.

Conductive fibrous materials

Abstract: As consistent with various embodiments, an electronic device includes a fibrous material having a conductive coating thereon. The conductive coating includes conductive nanoparticles coupled to fibers in the fibrous material. The structure is implemented in connection with a variety of devices, such as a capacitive device or a battery. Other embodiments are directed to forming conductive fibrous sheets, in dispersing a nanomaterial in a solution and applying the solution to a fibrous sheet, such as commercial paper, to form a conductive sheet.