Ji Young Kim

An open-framework iron fluoride and reduced graphene oxide nanocomposite as a high-capacity cathode material for Na-ion batteries

Cathode materials with high capacity and good stability for rechargeable Na-ion batteries (NIBs) are few in number. Here, we report a composite of electrochemically active iron fluoride hydrate and reduced graphene oxide (rGO) as a promising cathode material for NIBs. Phase-pure FeF3·0.5H2O is synthesized by a non-aqueous precipitation method and a composite with rGO is prepared to enhance the electrical conductivity. The encapsulation of FeF3·0.5H2O nanoparticles between the rGO layers results in a lightweight and stable electrode with a three-dimensional network. The composite material delivers a substantially enhanced discharge capacity of 266 mA h g−1 compared to 158 mA h g−1 of the bare FeF3·0.5H2O at a current density of 0.05 C. This composite also shows a stable cycle performance with a high capacity retention of >86% after 100 cycles, demonstrating its potential as a cathode material for NIBs.

Ordered SnO nanoparticles in MWCNT as a functional host material for high-rate lithium-sulfur battery cathode

Lithium-sulfur battery has become one of the most promising candidates for next generation batteries, and it is still restricted due to the low sulfur conductivity, large volume expansion and severe polysulfide shuttling. Herein, we present a novel hybrid electrode with a ternary nanomaterial based on sulfur-impregnated multiwalled carbon nanotubes filled with ordered tin-monoxide nanoparticles (MWCNT-SnO/S). Using a dry plasma reduction method, a mechanically robust material is prepared as a cathode host material for lithium-sulfur batteries. The MWCNT-SnO/S electrode exhibits high conductivity, good ability to capture polysulfides, and small volume change during a repeated charge–discharge process. In situ transmission electron microscopy and ultraviolet–visible absorption results indicate that the MWCNT-SnO host efficiently suppresses volume expansion during lithiation and reduces polysulfide dissolution into the electrolyte. Furthermore, the ordered SnO nanoparticles in the MWCNTs facilitate fast ion/electron transfer during the redox reactions by acting as connective links between the walls of the MWCNTs. The MWCNT-SnO/S cathode with a high sulfur content of 70 wt.% exhibits an initial discharge capacity of 1,682.4 mAh·g–1 at 167.5 mA·g–1 (0.1 C rate) and retains a capacity of 530.1 mAh·g–1 at 0.5 C after 1,000 cycles with nearly 100% Coulombic efficiency. Furthermore, the electrode exhibits the high capacity even at a high current rate of 20 C.

In situ fabrication of lithium titanium oxide by microwave-assisted alkalization for high-rate lithium-ion batteries

A phase-pure Li4Ti5O12/reduced graphene oxide nanocomposite was prepared using a simple one-pot synthesis of the Li–Ti–O precursor and subsequent heat treatment. The prepared nanocomposite delivers a reversible capacity of 168 mA h g−1 at 1 C-rate and a remarkable rate capability with 59% capacity retention at 50 C-rate.

Lipase-catalyzed resolution of primary alcohol containing quaternary chiral carbon

Summary2-Cyano-2-phenyl-1-hexanol containing chiral quaternary carbon was resolved using a lipase. Among various reaction conditions, transesterification reaction (solvent; n-hexane, lipase; Candida cylindracea) gave high selectivity(20/80). Additionally, the selectivity could be improved(13/87) when pyridine(1%) was used as an additive. The ratios of resolved alcohols were determined by GC and 1H-NMR analysis using Moshers derivative.

Li4SiO4-Based Artificial Passivation Thin Film for Improving Interfacial Stability of Li Metal Anodes

An amorphous SiO2 (a-SiO2) thin film was developed as an artificial passivation layer to stabilize Li metal anodes during electrochemical reactions. The thin film was prepared using an electron cyclotron resonance-chemical vapor deposition apparatus. The obtained passivation layer has a hierarchical structure, which is composed of lithium silicide, lithiated silicon oxide, and a-SiO2. The thickness of the a-SiO2 passivation layer could be varied by changing the processing time, whereas that of the lithium silicide and lithiated silicon oxide layers was almost constant. During cycling, the surface of the a-SiO2 passivation layer is converted into lithium silicate (Li4SiO4), and the portion of Li4SiO4 depends on the thickness of a-SiO2. A minimum overpotential of 21.7 mV was observed at the Li metal electrode at a current density of 3 mA cm-2 with flat voltage profiles, when an a-SiO2 passivation layer of 92.5 nm was used. The Li metal with this optimized thin passivation layer also showed the lowest charge-transfer resistance (3.948 Ω cm) and the highest Li ion diffusivity (7.06 × 10-14 cm2 s-1) after cycling in a Li-S battery. The existence of the Li4SiO4 artificial passivation layer prevents the corrosion of Li metal by suppressing Li dendritic growth and improving the ionic conductivity, which contribute to the low charge-transfer resistance and high Li ion diffusivity of the electrode.

Electronic structural studies on the improved thermal stability of Li(Ni0.8Co0.15Al0.05)O2 by ZrO2 coating for lithium ion batteries

AbstractThe electronic structures of bare and ZrO2-coated Li(Ni0.8Co0.15Al0.05)O2 electrode systems were investigated using a combination of time-resolved X-ray diffraction and soft X-ray absorption spectroscopy (XAS) techniques. The ZrO2 coating on the surface of Li(Ni0.8Co0.15Al0.05)O2 was effective in elevating the onset temperature of the dissociation of charged Li0.33(Ni0.8Co0.15Al0.05)O2, which will enhance the safety of Li-ion cells. Soft XAS spectra of the Ni LII,III-edge in the partial electron yield mode were obtained, which showed that the enhanced electrochemical properties and thermal stability of the cathode materials by ZrO2 coating can be attributed to the suppression of unwanted Ni oxidation state changes at the surface.Graphical AbstractThe electronic structural effects of a ZrO2 coating on Li(Ni0.8Co0.15Al0.05)O2 were examined by soft X-ray absorption spectroscopy. The coating stabilized the Ni oxidation state at the electrode surface against decompositionn

China's aggressive ‘periphery diplomacy’ and South Korean perspectives

ABSTRACT In this special section, the present article reviews South Korean perspectives on Chinas ‘periphery diplomacy’ with a focus on Chinese behaviour with respect to the East China Sea maritime territory and the Asian Infrastructure Investment Bank (AIIB). By analysing research papers published by various Korean research institutions and academic journals, this article demonstrates that most Korean scholars hold that as long as Chinas growth goes on, the tensions between the US and China are likely to intensify. The article also shows that one of the primary concerns of South Korean scholars lies in the question of how South Korea should respond to changing regional orders and a rising China. The article argues that South Koreas strategic dilemma is reflected in a regional structure in which competition between two great powers has recently forced the periphery to impose bilateral ties on.

Self-Relaxant Superelastic Matrix Derived from C60 Incorporated Sn Nanoparticles for Ultra-High-Performance Li-Ion Batteries

Homogeneously dispersed Sn nanoparticles approximately ⩽10 nm in a polymerized C60 (PC60) matrix, employed as the anode of a Li-ion battery, are prepared using plasma-assisted thermal evaporation coupled by chemical vapor deposition. The self-relaxant superelastic characteristics of the PC60 possess the ability to absorb the stress-strain generated by the Sn nanoparticles and can thus alleviate the problem of their extreme volume changes. Meanwhile, well-dispersed dot-like Sn nanoparticles, which are surrounded by a thin SnO2 layer, have suitable interparticle spacing and multilayer structures for alleviating the aggregation of Sn nanoparticles during repeated cycles. The Ohmic characteristic and the built-in electric field formed in the interparticle junction play important roles in enhancing the diffusion and transport rate of Li ions. SPC-50, a Sn-PC60 anode consisting of 50 wt % Sn and 50 wt % PC60, as confirmed by energy-dispersive X-ray spectroscopy analysis, exhibited the highest electrochemical performance. The resulting SPC-50 anode, in a half-cell configuration, exhibited an excellent capacity retention of 97.18%, even after 5000 cycles at a current density of 1000 mA g-1 with a discharge capacity of 834.25 mAh g-1. In addition, the rate-capability performance of this SPC-50 half-cell exhibited a discharge capacity of 544.33 mAh g-1 at a high current density of 10u202f000 mA g-1, even after the current density was increased 100-fold. Moreover, a very high discharge capacity of 1040.09 mAh g-1 was achieved with a capacity retention of 98.67% after 50 cycles at a current density of 100 mA g-1. Futhermore, a SPC-50 full-cell containing the LiCoO2 cathode exhibited a discharge capacity of 801.04 mAh g-1 and an areal capacity of 1.57 mAh cm-2 with a capacity retention of 95.27% after 350 cycles at a current density of 1000 mA g-1.

Icephobic performance on the aluminum foil-based micro-/nanostructured surface*

The research of superhydrophobic materials has attracted many researchers attention due to its application value and prospects. In order to expand the serviceable range, people have investigated various superhydrophobic materials. The simple and easy preparation method has become the focus for superhydrophobic materials. In this paper, we present a program for preparing a rough surface on an aluminum foil, which possesses excellent hydrophobic properties after the treatment with low surface energy materials at high vacuum. The resulting contact angle is larger than 160 degrees, and the droplet cannot freeze on the surface above 10 degrees C. Meanwhile, the modified aluminum foil with the thickness of less than 100 mu m can be used as an ideal flexible applied material for superhydrophobicity/anti-icing.