• Bulletin of the Korean Chemical Society
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• v.21 no.11
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• pp.1125-1132
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• 2000

The pH effect of the precursor solution on the preparation of $LiCoO_2$ by a solution phase reaction containing malonic acid was carried out. Layered $LiCoO_2$ powders were obtained with the precursors prepared at the different pHs (4, 7, and 9) and heat-treated at $700^{\circ}C(LiCoO_2-700)$ or $850^{\circ}C(LiCoO_2-850)$ in air. pHs of the media for precursor synthesis affects the charge/discharge and electrochemical properties of the $LiCoO_2electrodes.$ Upon irrespective of pH of the precursor media, X-ray diffraction spectra recorded for $LiCoO_2-850$ powder showed higher peak intensity ratio of I(003)/I(104) than that of $LiCoO_2-700$, since the better crystallization of the former crystallized better. However, $LiCoO_2$ synthesized at pH 4 displayed an abnormal higher intensity ratio of I(003)/I(104) than those synthesized at pH 7 and 9. The surface morphology of the $LiCoO_2-850$ powders was rougher and more irregular than that of $LiCoO_2-700$ made from the precursor synthesized at pH 7 and 9. The $LiCoO_2electrodes$ prepared with the precursors synthesized at pH 7 and 9 showed a better electrochemical and charge/discharge characteristics. From the AC impedance spectroscopic experiments for the electrode made from the precursor prepared in pH 7, the chemical diffusivity of Li ions (DLi+) in $Li0.58CoO_2determined$ was 2.7 ${\times}$10-8 $cm^2s-1$. A cell composed of the $LiCoO_2-700$ cathode prepared in pH 7 with Lithium metal anode reveals an initial discharge specific capacity of 119.8 mAhg-1 at a current density of 10.0 mAg-1 between 3.5 V and 4.3 V. The full-cell composed with $LiCoO_2-700$ cathode prepared in pH 7 and the Mesocarbon Pitch-based Carbon Fiber (MPCF) anode separated by a Cellgard 2400 membrane showed a good cycleability. In addition, it was operated over 100 charge/discharge cycles and displayed an average reversible capacity of nearly 130 mAhg-1.

• Applied Chemistry for Engineering
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• v.33 no.5
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• pp.459-465
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• 2022

A pitch coating method was proposed for the purpose of improving the electrochemical properties of natural graphite. The synthesis conditions of pitch coating were optimized via measuring electrochemical properties of pitch-coated graphite anodes. As the synthesis temperature increased, the thermal stability was improved in addition to an increase in the softening point and residual carbon weight. However, the synthesis temperature of 430 ℃ resulted in the synthesis of a large amount of NI (NMP Insoluble) due to excessive condensation reaction. As the surface uniformity and coating thickness increased due to high thermal stability, the initial coulombic efficiency and rate capability of the pitch-coated graphite were improved. However, the graphite coated with the pitch containing excessive NI showed lower electrochemical properties than the uncoated graphite. NI had low dispersibility and formed spheres after heat treatment, so it formed the heterogeneous and thicker SEI layer. The optimum conditions for forming a uniform surface and an appropriate coating layer were investigated.

• Clean Technology
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• v.29 no.3
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• pp.178-184
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• 2023

Transition metal chalcogenides have garnered significant attention as anode materials for sodium-ion batteries due to their high theoretical capacity. Nevertheless, their practical application is impeded by their limited lifespan resulting from substantial volume expansion during cycling and their low electrical conductivity. To tackle these issues, this study devised a solution by synthesizing a nanostructured anode material composed of porous CNT (carbon nanotube) spheres and (Ni,Co)Se₂ nanocrystals. By employing spray pyrolysis and subsequent heat treatments, a porous-structured (Ni,Co)Se₂-CNT composite microsphere was successfully synthesized, and its electrochemical properties as an anode for sodium-ion batteries were evaluated. The synthesized (Ni,Co)Se₂-CNT microsphere possesses a porous structure due to the nanovoids that formed as a result of the decomposition of the polystyrene (PS) nanobeads during spray pyrolysis. This porous structure can effectively accommodate the volume expansion that occurs during repeated cycling, while the CNT scaffold enhances electronic conductivity. Consequently, the (Ni,Co)Se₂-CNT anode exhibited an initial discharge capacity of 698 mA h g^-1 and maintained a high discharge capacity of 400 mA h g^-1 after 100 cycles at a current density of 0.2 A g^-1.

• Korean Journal of Agricultural Science
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• v.9 no.2
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• pp.540-545
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• 1982

An energy metabolism study was conducted with two commercial strains of meat-type chickens, Hubbard and Cobb, and two egg strains, Hy Line and Korean-bred Hanhyup 325. The heat production of growing chickens from each strain were measured by the use of an open-circuit gravimetric respiration calorimeter. The data obtained from this study were summarized as fallows. 1. The average body weight of 9-wk-old Hubbard broilers reared in battery cages was 2,570g/bird. The average body weights of 9-wk-old Hy Line chicks and Hanhyup 325 were 777 and 748g/bird, respectively. 2. At 3 weeks of age, the Hubbard broiler chicks consumed two times the feed consumed by Hy Line chicks (54.6g VS. 26.7g/bird/day). These values increased to 151g and 57.2g/bird/day, respectively, at 8 weeks of age, indicating that the difference in feed intake between meat and egg-type chicks tends to increase as they grow older. In terms of water consumption, the 5-wk-old Hubbard broiler chicks drank $226m{\ell}/bird/day$ as compared with $58m{\ell}$ by Hy Line chicks. These values increased to 282 and $70m{\ell}$, respectively, at 8 weeks of age. 3. The excreta outputs of Hubbard broilers and Hy Line chicks were 18.7 and 6.1g DM/bird/day at 4 weeks of age, and 41.5 and 10.0g DM/bird/day at 8 weeks of age, respectively. 4. The energy metabolizability of broiler chicks were 75.4~77.1% compared to 75.0~83.5% by egg-type chicks. 5. The respiratory quotient (RQ) was between 0.78 and 0.97. There seems to be no difference in RQ between meat and egg-type chicks. The RQ tended to decrease when feed intake was low and vice versa. 6. Both meat and egg-type chicks produced $83.1{\sim}123.1Kcal/kg^{\frac{3}{4}}B.W./day$. The considerably low value of $83Kcal/kg^{\frac{3}{4}}B.W./day$ was obtained when the chicks were off the feed under the stressful conditions. The high value of 123.1Kcal was obtained when the chicken chamber temperature rose to $27{\sim}34^{\circ}C$.

• Clean Technology
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• v.24 no.1
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• pp.77-84
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• 2018

In this study, $Li_4Ti_5O_{12}$ anode materials for lithium ion battery were synthesized by dry ball-mill method. Polyvinyl chloride (PVC) as a carbon source was added to improve electrochemical properties. When the PVC was added after $Li_4Ti_5O_{12}$ formation, the spinel structure was well synthesized and it was confirmed by X-ray diffraction (XRD) experiments. When the carbon material was added before the synthesis and the heat treatment was performed, it was confirmed that a material having a different crystal structure was synthesized even when a small amount of carbon material was added. In the case of $Li_4Ti_5O_{12}$ without the carbon material, the electrical conductivity value was about $10{\mu}S\;m^{-1}$, which was very small and similar to that of the nonconductor. As the carbon was added, the electrical conductivity was greatly improved and increased up to 10,000 times. Electrochemical impedance spectroscopy (EIS) analysis showed that the size of semicircle corresponding to the resistance decreased with the carbon addition. This indicates that the resistance inside the electrode is reduced. According to the Cyclic voltammetry (CV) analysis, the potential difference between the oxidation peak and the reduction peak was reduced with carbon addition. This means that the rate of lithium ion insertion and deinsertion was increased. $Li_4Ti_5O_{12}$ with 9.5 wt% PVC added sample showed the best properties in rate capabilities of $180mA\;h\;g^{-1}$ at 0.2 C-rate, $165mA\;h\;g^{-1}$ at 0.5 C-rate, and $95.8mA\;h\;g^{-1}$ at 5 C-rate.