• Membrane Journal
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• v.17 no.3
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• pp.233-243
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• 2007

In this study, a separate. which is a microporous membrane based on poly(vinylidene fluoride)(PVdF) was prepared by phase inversion method. Being prepared by dissolving the PVdF in the N,N'-dimethylformamide(DMF) with mechanical stirring, the homogenous casting solution was cast onto a clean glass plate. Pore size and porosity of the membranes were controlled by changing preparation condition. The highest porosity of the membrane was 78.6%. The mechanical property of the membrane was determined by using an universal testing machine(UTM). The morphology of the membrane was investigated by scanning electron microscopy(SEM). The cross-section of the membrane shows sponge-like small micro-pores.

• Journal of KIISE:Databases
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• v.35 no.3
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• pp.208-217
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• 2008

Sensors have a function to gather environment-related information operating by small-size battery in sensor networks. The issue related with energy is still an important in spite of the recent advancements in micro-electro-mechanical-system(MEMS) related techology. Generally it is assumed that replacement or rechargement of battery power in sensor is not feasible and a message send operation may spend at least 1000 times battery than a local operation. Thus, there have been several kinds of research efforts to lessen the number of unnecessary messages by maintaining the information of the other neighboring(or all) sensors. In this paper, we propose an index structure based on parent-children relationship to the purpose. Namely, parent node gathers the set of location information and MBA per child. It's named PH and may allow to process the range query with higher accurate and small size information. Through extensive experiments, we show that our index structure has better energy consumption.

• Korean Journal of Materials Research
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• v.21 no.1
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• pp.21-27
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• 2011

A nano-porous structure of tin oxide was prepared using an anodic oxidation process and the sample's electrochemical properties were evaluated for application as an anode in a rechargeable lithium battery. Microscopic images of the as-anodized sample indicated that it has a nano-porous structure with an average pore size of several tens of nanometers and a pore wall size of about 10 nanometers; the structural/compositional analyses proved that it is amorphous stannous oxide (SnO). The powder form of the as-anodized specimen was satisfactorily lithiated and delithiated as the anode in a lithium battery. Furthermore, it showed high initial reversible capacity and superior rate performance when compared to previous fabrication attempts. Its excellent electrode performance is probably due to the effective alleviation of strain arising from a cycling-induced large volume change and the short diffusion length of lithium through the nano-structured sample. To further enhance the rate performance, the attempt was made to create porous tin oxide film on copper substrate by anodizing the electrodeposited tin. Nevertheless, the full anodization of tin film on a copper substrate led to the mechanical disintegration of the anodic tin oxide, due most likely to the vigorous gas evolution and the surface oxidation of copper substrate. The adhesion of anodic tin oxide to the substrate, together with the initial reversibility and cycling stability, needs to be further improved for its application to high-power electrode materials in lithium batteries.

• Bulletin of the Korean Chemical Society
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• v.35 no.2
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• pp.357-364
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• 2014

Size controlled, $LiNi_{0.8}Co_{0.15}Al_{0.05}O_2$ cathode powders were prepared by co-precipitation method followed by heat treatment at temperatures between 750 and $850^{\circ}C$. The synthesized samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance. The synthesized $LiNi_{0.8}Co_{0.15}Al_{0.05}O_2$ after calcined at $750^{\circ}C$ has a good electrochemical performance with an initial discharge capacity of $190mAhg^{-1}$ and good capacity retention of 100% after 30 cycles at 0.1C ($17mAg^{-1}$). The capacity retention of $LiNi_{0.8}Co_{0.15}Al_{0.05}O_2$ after calcined at $750^{\circ}C$ is better than that at 800 and $850^{\circ}C$ without capacity loss at various high C rates. This is ascribed to the minimized cation disorder, a higher conductivity, and higher lithium ion diffusion coefficient ($D_{Li}$) observed in this material. In the differential scanning calorimetry DSC profile of the charged sample, the generation of heat by exothermic reaction was decreased by calcined at high temperature, and this decrease is especially at $850^{\circ}C$. This behavior implies that the high temperature calcinations of $LiNi_{0.8}Co_{0.15}Al_{0.05}O_2$ prevent phase transitions with the release of oxygen.

• Korean Chemical Engineering Research
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• v.56 no.1
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• pp.42-48
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• 2018

Silicon has attracted extensive attention due to its high theoretical capacity, low discharge potential and non-toxicity as anode material for lithium ion batteries. In this study, Si-CNT-C composites were fabricated for use as a high-efficiency anode material in a lithium ion battery. Aerosol self-assembly and post-heat treatment processes were employed to fabricate the composites. The morphology of the Si-CNT-C composites was spherical and an average particle size was $2.72{\mu}m$. The size of the composite increased as concentration of Si and CNT increased in the precursor solution. In the Si-CNT-C composites, CNT and C carbonized from glucose were attached to the surface of Si particles. Electrochemical measurement showed that the cycle performance of Si-CNT-C composites was better than that of silicon particles.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.4
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• pp.504-511
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• 2011

Nano-sized Sn powder was prepared by pulsed wire evaporation method. The Sn powder and carbon black were charged in jar and ball milled. The milling time was varied with 10 min., 1h, 2h, and 4h, respectively. The milled powders were dried and the shape and size were observed by FE-SEM. Nano-sized Sn powders were plastic-deformed and agglomerated by impact force of balls and heat generated during the SPEX milling. The agglomerated Sn powder also consisted of many nano-sized particles. Initial discharge capacities of milled Sn electrode powders with carbon powder were milled for 10 min., 1h, 2h, and 4h were 787, 829, 827, and 816 mAh/g, respectively. After 5 cycle, discharge capacities of Sn electrode powders with carbon powder milled for 10 min., 1h, 2h, and 4h decreased as 271, 331, 351, and 287 mAh/g, respectively. Because Sn electrode powders milled for 2h constist of uniform and fine size, the cyclability of coin cell made of this powders is better than others.

• Journal of the Korean Ceramic Society
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• v.44 no.5 s.300
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• pp.148-150
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• 2007

A process to synthesize $La_{0.8}Sr_{0.2}CrO_3$ (LSC), which is a promising material for use as a separator in a soild oxide fuel cell, is investigated in this study. LSC powders without secondary Phases could be synthesized with ultrasonic spray pyrolysis and a heat treatment at $1200^{\circ}C$ for 20 h; however, it showed an average diameter of $0.6{\mu}m$ with a wide particle size distribution. On the other hand, LSC powders synthesized with spray pyrolysis at $800^{\circ}C$, heat-treated at $900^{\circ}C$ for 5 h, ball-milled and finally heat-treated again at $1200^{\circ}C$ for 20 h showed a smaller average diameter of $0.3{\mu}m$ and narrower size distribution. Very few particles above $0.5{\mu}m$ were found. Thus, a proper combination of the heat treatment and milling process after spray pyrolysis it determined to be very important in synthesizing fine and uniform LSC perovskite powders.

• Journal of the Korean Vacuum Society
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• v.9 no.1
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• pp.36-41
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• 2000

$SnO-2$ thin films for thin film secondary battery anode were deposited n glass substrate with stain-less steel collector and charge/discharge experiments were conducted to investigate feasibility of $SnO-2$ thin film as a new anode material. The as-deposited films were pure $SnO-2$ phase which is not related to deposition condition. The grain size on the surface of as-deposited films increased with increase of oxygen partial pressure. However, the grain size did not show any change above oxygen partial pressure of 80:20. The surface roughness of the as-deposited films increased after decreasing because of resputtering effect of oxygen negative ion in plasma. All films showed typical $SnO-2$ anode characteristics which has a side effect at the first cycle, which is not related to the deposition condition. The charge/discharge experiments of 200cycles indicated that capacity of $SnO-2$ films depended on oxygen contents and surface roughness. The cycle characteristics was determined by initial charge/discharge reaction. The $SnO-2$ film with low initial capacity showed more stable cycle characteristics than film with high initial capacity.

• Journal of Electrochemical Science and Technology
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• v.10 no.1
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• pp.89-97
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• 2019

As a promising candidate for anode materials in lithium ion battery (LIB), tungsten trioxide ($WO_3$) and tungsten disulfide ($WS_2$) nanocrystals were synthesized, and their electrochemical properties were comprehensibly studied using a half cell. One-dimensional $WO_3$ nanowires with uniform diameter of 10 nm were synthesized by hydrothermal method, and two-dimensional (2D) $WS_2$ nanosheets by unique gas phase sulfurization of $WO_3$ using $H_2S$. $WS_2$ nanosheets exhibits uniformly 10 nm thickness. The $WO_3$ nanowires and $WS_2$ nanosheets showed maximum capacities of 552 and $633mA\;h\;g^{-1}$, respectively, after 100 cycles. Especially, the capacity of $WS_2$ is significantly larger than the theoretical capacity ($433mA\;h\;g^{-1}$). We also examined the cycling performance using a larger size $WO_3$ and $WS_2$ nanocrystals, showing that the smaller size plays an important role in enhancing the capacity of LIBs. The larger capacity of $WS_2$ nanosheets than the theoretical value is ascribed to the lower charge transfer resistance of 2D nanostructures.

• Korean Chemical Engineering Research
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• v.55 no.2
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• pp.163-169
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• 2017

In order to investigate the electrochemical properties and the particle size effect of $LiNi_{1-x-y}Co_xAl_yO_2$ (x=0.15, y=0.045 or 0.05, NCA) for lithium ion batteries (LIBs), two commercial NCA cathode materials (NCA#1, NCA#2) were used as cathode materials for LIB. The average particle size of the NCA#1 which consisted of uniform spherical particles was found to be approximately $5m{\mu}$. NCA#2 consisted of particles with bimodal size distribution of approximately $5m{\mu}$ and $11m{\mu}$. From the results of charge-discharge performance test, a high initial discharge capacity of 197.0 mAh/g was obtained with NCA#2, which is a higher value than that with NCA#1. The cycle retentions of NCA#1 and NCA#2 up to 30 cycles were 92% and 94%, respectively.