Jun-Ho Park

Silicon/Carbon Nanotube/BaTiO3 Nanocomposite Anode: Evidence for Enhanced Lithium-Ion Mobility Induced by the Local Piezoelectric Potential

We report on the synergetic effects of silicon (Si) and BaTiO3 (BTO) for applications as the anode of Li-ion batteries. The large expansion of Si during lithiation was exploited as an energy source via piezoelectric BTO nanoparticles. Si and BTO nanoparticles were dispersed in a matrix consisting of multiwalled carbon nanotubes (CNTs) using a high-energy ball-milling process. The mechanical stress resulting from the expansion of Si was transferred via the CNT matrix to the BTO, which can be poled, so that a piezoelectric potential is generated. We found that this local piezoelectric potential can improve the electrochemical performance of the Si/CNT/BTO nanocomposite anodes. Experimental measurements and simulation results support the increased mobility of Li-ions due to the local piezoelectric potential.

Enhancement in the electrochemical performance of zirconium/phosphate bi-functional coatings on LiNi0.8Co0.15Mn0.05O2 by the removal of Li residuals

The effect of bi-functional coatings consisting of Zr and phosphate (P) on the electrochemical performance of Li1.0Ni0.8Co0.15Mn0.05O2 (NCM) has been investigated. The presence of various types of Zr and P compounds such as oxides (ZrO2 and Li2ZrO3) and phosphates (Zr2P2O9, ZrP2O7 and LiZr2(PO4)3) in the coating was confirmed by experiments as well as density functional theory (DFT) calculations. When the NCM samples were coated with the Zr/P hybrid material, the cycle retention and the amount of removed Li residuals (LiOH, Li2CO3) were enhanced by the synergistic effect from Zr and P. The NCM sample coated with a Zr/P layer with a Zr/P ratio of 1u2009:u20091 exhibited an increase in the initial capacity (209.3 mA h g-1) compared to the pristine sample (207.4 mA h g-1) at 0.1C, owing to the formation of the coating layer. The capacity retention of the Zr/P coated sample (92.4% at the 50th cycle) was also improved compared to that of the pristine NCM sample (90.6% at the 50th cycle). Moreover, the amount of Li residuals in the Zr/P coated NCM sample was greatly reduced from 3693 ppm (pristine NCM) to 2525 ppm (Zr/P = 5u2009:u20095).

Continuous plasma separation from whole blood using microchannel geometry

Plasma separation from whole blood using microfluidics was investigated. We suggested modified channel geometry called corner-edge to enhance plasma skimming effect at branching channel. To evaluate separation efficiency, microfluidic chip was fabricated with silicone elastomer and glass. The efficiency of separation was above 99% comparing with whole blood hematocrit. This microfluidic unit could be integrated with microchannel network for lab-on-a-chip applications such as immunoassay.

Re-construction layer effect of LiNi 0.8 Co 0.15 Mn 0.05 O 2 with solvent evaporation process

The solvent evaporation method on the structural changes and surface chemistry of the cathode and the effect of electrochemical performance of Li1.0Ni0.8Co0.15Mn0.05O2 (NCM) has been investigated. After dissolving of Li residuals using minimum content of solvent in order to minimize the damage of pristine material and the evaporation time, the solvent was evaporated without filtering and remaining powder was re-heated at 700u2009°C in oxygen environment. Two kinds of solvent, de-ionized water and diluted nitric acid, were used as a solvent. The almost 40% of Li residuals were removed using solvent evaporation method. The NCM sample after solvent evaporation process exhibited an increase in the initial capacity (214.3u2009mAh/g) compared to the pristine sample (207.4u2009mAh/g) at 0.1C because of enhancement of electric conductivity caused by decline of Li residuals. The capacity retention of NCM sample after solvent evaporation process (96.0% at the 50th cycle) was also improved compared to that of the pristine NCM sample (90.6% at the 50th cycle). The uniform Li residual layer after solvent treated and heat treatment acted like a coating layer, leading to enhance the cycle performance. The NCM sample using diluted nitric acid showed better performance than that using de-ionized water.

Improving the kinetics and surface stability of sodium manganese oxide cathode materials for sodium rechargeable batteries with Al2O3/MWCNT hybrid networks

We report the design and fabrication of a novel functional material in which protective Al2O3 nanoparticles are merged with highly conductive multi-walled carbon nanotubes (MWCNTs). In this paper, we discuss in detail the effects of the Al2O3/MWCNT hybrid networks on the electrochemical performance of sodium manganese oxide (Na0.44MnO2), which is used as an electrode material in sodium rechargeable batteries. The Al2O3/MWCNT hybrid networks, which are uniformly dispersed on the surface of Na0.44MnO2, change its surface bonding nature, resulting in an improvement in the cycling performance and rate capability of Na0.44MnO2. We ascribe these enhancements in performance to the inhibition of the formation of damaging NaF-based solid-electrolyte interface (SEI) layers during cycling, which enables facile transfer of Na ions through the Na0.44MnO2 electrode/electrolyte interface. Our findings regarding the control of the chemistry and bonding structure of the Na0.44MnO2 particle surfaces induced by the introduction of the Al2O3/MWCNT functional hybrid networks provide insight into the possibilities for achieving sodium rechargeable batteries with high power density and stability.

Statistical Analysis on Static Recrystallization Texture Evolution in Cold-Rolled AZ31 Magnesium Alloy Sheet

Cast AZ31B-H24 magnesium alloy, comprising Mg with 3.27 wt% Al and 0.96 wt% Zn, was cold rolled and subsequently annealed. Global texture evolutions in the specimens were observed by X-ray diffractometry after the thermomechanical processing. Image-based microstructure and texture for the deformed, recrystallized, and grown grains were observed by electron backscattered diffractometry. Recrystallized grains could be distinguished from deformed ones by analyzing grain orientation spread. Split basal texture of ca. ±10-15° in the rolling direction was observed in the cold-rolled sample. Recrystallized grains had widely spread basal poles at nucleation stage; strong {0001} basal texture developed with grain growth during annealing.

Tetrathiafulvalene as a Conductive Film-Making Additive on High-Voltage Cathode

Tetrathiafulvalene (TTF) is investigated as a conductive film-making additive on an overlithiated layered oxide (OLO) cathode. When the OLO/graphite cell is cycled at high voltage, carbonate-based electrolyte without the additive decomposes continuously to form a thick and highly resistant surface film on the cathode. In contrast, TTF added into the electrolyte becomes oxidized before the electrolyte solvents, creating a thinner film on the cathode surface. This film inhibits further electrolyte decomposition through cycling and stabilizes the interface between the cathode and the electrolyte. The cells containing the OLO cathode with TTF-added electrolyte afforded enhanced capacity retention and rate capability, making TTF a prospective electrolyte additive for higher energy density lithium-ion cells.

Single red blood cell deformability test using optical trapping in plastic microfluidic chip

In this study, single red blood cell (RBC) deformability test is performed by using optical trapping in poly(dimethylsiloxane) PDMS microfluidic chip. The salient feature of this method is to provide more extensional recovery time of individual RBCs in order to tell the minor difference of RBC deformability between normal and abnormal blood.

Development of a Cylindrical Neutron Generator using RF-driven Plasma

A compact cylindrical neutron generator using RF (radio-frequency) inductively-coupled plasma has been developed in radially convergent ion beam extraction configuration. Since the RF plasma source has characteristics of high plasma density, low gas pressure, high mono-atomic fraction, and long lifetime, it is known to be suitable for generating high neutron yield with high efficiency. In order to increase neutron yield, the energy and the number of incident particles should be as large as possible. Since the cylindrical source can be operated as a line source configuration the extracted beam current can be increased easily. In this paper, experimental results with the cylindrical neutron generator are given and the operating characteristics of the device are discussed to improve neutron generation efficiency

Development of micro Hemocytometer for human erythrocyte analysis for the early detection of cancer

The relation between erythrocyte deformability and cancer has been proved in medical fields, but it is very difficult to systemize and commercialize the traditional schemes for erythrocyte deformability assessment. In this work, a desk-top type RBC Hemocytometer system with PDMS microchip has been developed for the assessment. Macrochannels with microfiltering structure in the microchip make the erythrocyte deformed, and with an UV optical array system and C language based image processing software, filter-pass-shape and filter-pass-velocity of erythrocytes are sequentially analyzed. In the comparative studies with blood from cancerous patients and control blood, we could obtain statistically acceptable data that can distinguish cancerous from control regardless of the cancer infected regions. To enhance the performance of the system, comparative studies changing the materials of the chip (silicon-glass, PDMS and PMMA) and sectional surface characteristics control have been accomplished with notable results. This RBC Hemocytometer system can be applied as a practical diagnostic apparatus in early detection of cancer.