Seung Deok Seo

Highly Reversible Lithium Storage in Bacillus subtilis-Directed Porous Co3O4 Nanostructures

In this work, a simple, high-yield biomineralization process is reported for cobalt oxide nanostructures using Gram-positive bacteria, Bacillus subtilis , as the soft templates. Rod-type cobalt oxide is prepared at room temperature through an electrostatic interaction between the functional surface structures of the bacteria and the cobalt ions in an aqueous solution. Additionally, porous Co₃O₄ hollow rods are formed through a subsequent heat treatment at 300 °C. These rods have a high surface area and exhibited an excellent electrochemical performance for rechargeable Li-ion batteries. This facile, inexpensive, and environmentally benign synthesis for transition metal oxides with unique nanostructures can be used for several practical applications, such as batteries, catalysts, sensors, and supercapacitors.

A binder-free Ge-nanoparticle anode assembled on multiwalled carbon nanotube networks for Li-ion batteries

Germanium (Ge) nanoparticle-multiwalled carbon nanotube (MWCNT) anodes are fabricated through the anchoring of Ge on the surface of electrophoretically pre-deposited MWCNT networks via a thermal evaporation process. This Ge-MWCNT nanocomposite displays a large reversible capacity of over 800 mA h g(-1) at 1 C even after 200 cycles.

Scalable One-pot Bacteria-templating Synthesis Route toward Hierarchical, Porous-Co3O4 Superstructures for Supercapacitor Electrodes

Template-driven strategy has been widely used to synthesize inorganic nano/micro materials. Here, we used a bottom-up controlled synthesis route to develop a powerful solution-based method of fabricating three-dimensional (3D), hierarchical, porous-Co3O4 superstructures that exhibit the morphology of flower-like microspheres (hereafter, RT-Co3O4). The gram-scale RT-Co3O4 was facilely prepared using one-pot synthesis with bacterial templating at room temperature. Large-surface-area RT-Co3O4 also has a noticeable pseudocapacitive performance because of its high mass loading per area (~10 mg cm−2), indicating a high capacitance of 214 F g−1 (2.04 F cm−2) at 2 A g−1 (19.02 mA cm−2), a Coulombic efficiency averaging over 95%, and an excellent cycling stability that shows a capacitance retention of about 95% after 4,000 cycles.

Synthesis of core/shell spinel ferrite/carbon nanoparticles with enhanced cycling stability for lithium ion battery anodes

Monodispersed core/shell spinel ferrite/carbon nanoparticles are formed by thermolysis of metal (Fe3+, Co2+) oleates followed by carbon coating. The phase and morphology of nanoparticles are characterized by x-ray diffraction and transmission electron microscopy. Pure Fe3O4 and CoFe2O4 nanoparticles are initially prepared through thermal decomposition of metal–oleate precursors at 310 degrees C and they are found to exhibit poor electrochemical performance because of the easy aggregation of nanoparticles and the resulting increase in the interparticle contact resistance. In contrast, uniform carbon coating of Fe3O4 and CoFe2O4 nanoparticles by low-temperature (180 degrees C) decomposition of malic acid allowed each nanoparticle to be electrically wired to a current collector through a conducting percolative path. Core/shell Fe3O4/C and CoFe2O4/C nanocomposite electrodes show a high specific capacity that can exceed 700 mAh g(-1) after 200 cycles, along with enhanced cycling stability.

Heteroepitaxial growth of ZnO nanosheet bands on ZnCo2O4 submicron rods toward high-performance Li ion battery electrodes

AbstractWe report the direct synthesis of ZnCo2O4 and ZnO/ZnCo2O4 submicron rod arrays grown on Ni foil current collectors via an ammonia-evaporation-induced method by controlling the ratio of Zn to Co. These three-dimensional (3D) hierarchical self-supported nanostructures are composed of one-dimensional (1D) ZnCo2O4 rods and two-dimensional (2D) ZnO nanosheet bands perpendicular to the axis of the each ZnCo2O4 rod. We carefully deal with the heteroepitaxial growth mechanisms of hexagonal ZnO nanosheets from a crystallographic point of view. Furthermore, we demonstrate the ability of these high-surface-area ZnO/ZnCo2O4 heterostructured rods to enable improved electrolyte permeability and Li ion transfer, thereby enhancing their Li storage capability (∼900 mA·h·g−1 at a rate of 45 mA·h·g−1) for Li ion battery electrodes.

Enhancement of cyclability of urchin-like rutile TiO2 submicron spheres by nanopainting with carbon

Phase-pure urchin-like rutile TiO2 (U-TiO2) submicron (<1 μm) spheres composed of numerous single-crystalline nanorods are successfully synthesized using a surfactant-free wet-chemical route. In addition, a reliable mechanism for the formation of U-TiO2, different from the well-known “growth-then-assembly” mode, is suggested. To provide a highly electron-conducting network, the U-TiO2 submicron spheres are nanopainted with a conductive amorphous carbon layer. As anodes for Li-ion batteries, the carbon-coated U-TiO2 submicron sphere electrodes show enhanced cycling performance, maintaining a reversible capacity of 165.7 mA h g−1 after 100 cycles at a rate of 0.2 C; this is attributed to the provision of an efficient electron-transport path by the conductive carbon.

Low-temperature synthesis of CuO-interlaced nanodiscs for lithium ion battery electrodes

In this study, we report the high-yield synthesis of 2-dimensional cupric oxide (CuO) nanodiscs through dehydrogenation of 1-dimensional Cu(OH)2 nanowires at 60°C. Most of the nanodiscs had a diameter of approximately 500 nm and a thickness of approximately 50 nm. After further prolonged reaction times, secondary irregular nanodiscs gradually grew vertically into regular nanodiscs. These CuO nanostructures were characterized using X-ray diffraction, transmission electron microscopy, and Brunauer-Emmett-Teller measurements. The possible growth mechanism of the interlaced disc CuO nanostructures is systematically discussed. The electrochemical performances of the CuO nanodisc electrodes were evaluated in detail using cyclic voltammetry and galvanostatic cycling. Furthermore, we demonstrate that the incorporation of multiwalled carbon nanotubes enables the enhanced reversible capacities and capacity retention of CuO nanodisc electrodes on cycling by offering more efficient electron transport paths.

Electrochemical performance of NixCo1-xMoO4 (0 ≤ x ≤ 1) nanowire anodes for lithium-ion batteries.

NixCo1-xMoO4 (0 ≤ x ≤ 1) nanowire electrodes for lithium-ion rechargeable batteries have been synthesized via a hydrothermal method, followed by thermal post-annealing at 500°C for 2 h. The chemical composition of the nanowires was varied, and their morphological features and crystalline structures were characterized using field-emission scanning electron microscopy and X-ray powder diffraction. The reversible capacity of NiMoO4 and Ni0.75Co0.25MoO4 nanowire electrodes was larger (≈520 mA h/g after 20 cycles at a rate of 196 mA/g) than that of the other nanowires. This enhanced electrochemical performance of NixCo1-xMoO4 nanowires with high Ni content was ascribed to their larger surface area and efficient electron transport path facilitated by their one-dimensional nanostructure.

Direct assembly of tin–MWCNT 3D-networked anode for rechargeable lithium ion batteries

Nanocomposites of Sn nanoparticle–multiwalled carbon nanotubes (MWCNTs) were prepared by simple two-step electrochemical processes. First, acid-functionalized MWCNTs were electrophoretically deposited on a stainless steel substrate. Sn nanoparticles decorated on the MWCNTs were prepared by the electrodeposition of a SnCl4 aqueous solution on the pre-deposited MWCNT-film layer. The structure of the newly fabricated Sn-MWCNT composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The electrochemical performance of the composite was evaluated by cyclic voltammetry and galvanostatic cycling. The as-deposited composite film shows the size of the uniformly dispersed Sn particles, ranging from few to several tens of nanometres, as a function of the deposition time. The composite shows electrochemical performance that is superior to that of a pure Sn nanoparticle anode.

Superior long-term cycling stability of SnO2 nanoparticle/multiwalled carbon nanotube heterostructured electrodes for Li-ion rechargeable batteries

We demonstrate the fabrication of hybrid nanocomposite electrodes with a combination of SnO(2) nanoparticles (NPs) and conducting multiwalled carbon nanotube (MWCNT) anodes (SnO(2)@CNT) through the direct anchoring of SnO(2) NPs on the surface of electrophoretically pre-deposited MWCNT (EPD-CNT) networks via a metal-organic chemical vapor deposition process. This SnO(2)@CNT nanocomposite displays large reversible capacities of over 780, 510, and 470 mA h g(-1) at 1 C after 100, 500, and 1000 cycles, respectively. This outstanding long-term cycling stability is a result of the uniform distribution of SnO(2) NPs (~8.5 nm), a nanoscale EPD-CNT network with good electrical conductivity, and the creation of open spaces that buffer a large volume change during the Li-alloying/dealloying reaction of SnO(2).