• Journal of Power Electronics
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• v.18 no.3
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• pp.910-922
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• 2018

Conventional battery state-of-charge (SoC) estimation methods either involve sophisticated models or consume considerable computational resource. This study constructs an enhanced coulomb counting method (Ah method) for the SoC estimation of lithium-ion batteries (LiBs) by expanding the Peukert equation for the discharging process and incorporating the Coulombic efficiency for the charging process. Both the rate- and temperature-dependence of battery capacity are encompassed. An SoC mapping approach is also devised for initial SoC determination and Ah method correction. The charge counting performance at different sampling frequencies is analyzed experimentally and theoretically. To achieve a favorable compromise between sampling frequency and accumulation accuracy, a frequency-adjustable current sampling solution is developed. Experiments under the augmented urban dynamometer driving schedule cycles at different temperatures are conducted on two LiBs of different chemistries. Results verify the effectiveness and generalization ability of the proposed SoC estimation method.

• Bulletin of the Korean Chemical Society
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• v.32 no.10
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• pp.3726-3729
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• 2011

Biofilm formation is inevitable in a bioelectrochemical system in which microorganisms act as a sole biocatalyst. Cathodic biofilm (CBF) works as a double-edged sword in the performance of the air-cathode microbial fuel cells (MFCs). Proton and oxygen crossover through the CBF are limited by the robust structure of extracellular polymeric substances, composition of available constituents and environmental condition from which the biofilm is formed. The MFC performance in terms of power, current and coulombic efficiency is influenced by the nature and origin of CBF. Development of CBF from different ecological environment while keeping the same anode inoculums, contributes additional charge transfer resistance to the total internal resistance, with increase in coulombic efficiency at the expense of power reduction. This study demonstrates that MFC operation conditions need to be optimized on the choice of initial inoculum medium that leads to the biofilm formation on the air cathode.

• Journal of the Korean Electrochemical Society
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• v.5 no.4
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• pp.173-177
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• 2002

Electrochemical characteristics of a graphite/lithium and a $LiCoO_2/lithium$ half cell and a $graphite/LiCoO_2$ full cell were analyzed using a GCSOC (gradual control test of the state of charge) technique. The IIE (initial intercalation coulombic efficiency), which represents lithium intercalation property of the electrode material, and the $lIC_s$ (initial irreversible capacity by the surface), which represents irreversible reaction between the electrode surface and the electrolyte were obtained from the GCSOC analysis. Linear-fittable capacity ranges of IIE of graphite and $LiCoO_2$ electrodes were 370 and 150 mAh/g, respectively, based on material weight. The value of lIE for graphite and $LiCoO_2$ electrodes were $93-94\%$ and $94-95\%$, respectively. The value of IICs for graphite and $LiCoO_2$ electrodes were 15-17 mAh/g and 0.3-1.7 mAh/g, respectively. The value of IIE for $graphite/LiCoO_2$ full cell, used GX25 and DJG311 as a graphite, was $89-90\%$ that lower than that for the half cells. Parameters of IIE and IICs can also be used to represent not only half cell but also full cell.

• Bulletin of the Korean Chemical Society
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• v.25 no.6
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• pp.813-818
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• 2004

A systematic study of microbial fuel cells comprised of thermophilic Bacillus licheniformis and Bacillus thermoglucosidasius has been carried out under various operating conditions. Substantial amount of electricity was generated when a redox mediator was used. Being affected by operation temperature, the maximum efficiency was obtained at 50$^{\circ}C$ with an open circuit voltage of ca. 0.7 V. While a small change around the optimum temperature did not make much effect on the cell performance, the rapid decrease in performance was observed above 70$^{\circ}C$. It was noticeable that fuel cell efficiency and discharge pattern strongly depended on the kind of carbon sources used in the initial culture medium. In the case of B. thermoglucosidasius, glucose alone was utilized constitutively as a substrate in the microbial fuel cell irrespective of used carbons sources. When B. licheniformis was cultivated with lactose as a carbon source, best charging characteristics were recorded. Trehalose, in particular, showed 41.2% coulombic efficiency when B. thermoglucosidasius was cultured in a starch-containing medium. Relatively good repetitive operation was possible with B. thermoglucosidasius cells up to 12 cycles using glucose as a carbon source, when they were cultured with lactose as an initial carbon source. This study demonstrates that highly efficient thermophilic microbial fuel cells can be constructed by a pertinent modulation of the operating conditions and by carefully selecting carbon sources used in the initial culture medium.

• Journal of Microbiology and Biotechnology
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• v.11 no.5
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• pp.863-869
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• 2001

A systematic study of microbial fuel cells comprised of alkalophilic Bacillus sp. B-31 has been carried out under various operating conditions. A significant amount of electricity was generated when redox mediators were used. Among the phenothiazine-type redox dyes tested, azure A was found to be the most effective both in maintaining a high cell voltage and for the long-term operation. The maximum efficiency was and for the long-term operation. The maximum efficiency was obtained at ca. $50^{\circ}C$ giving an open circuit voltage of 0.7V. A small change in temperature did not significantly affect the cell performance, but a rapid decrease in performance was observed below $20^{\circ}C$ and above $70^{\circ}C$. It was noticeable that fuel cell efficiency and discharge pattern depended strongly on the carbon source used in the initial culture medium. Regardless of the initial carbon sources, only glucose and trehalose were utilized as substrates. Galactose, however, was not substantially utilized except when galactose was used in the initial medium. Glucose, in particular, showed $87\%$ coulombic efficiency, which was the highest value ever reported, when Bacillus sp. was cultured in a maltose-containing medium. This study demonstrates that highly efficient microbial fuel cells can be constructed with alkalophilic microorganisms by fine-tuning the operating conditions and by carefully selecting carbon sources in the initial culture medium.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.43-44
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• 2007

SiO and graphite composite has been prepared by adopting high energy ball milling technique. The anode material shows high initial discharge and charge capacity values of 1138 and 568 mAh/g, respectively. Since the materials formed during initial discharge process the nano silicon/$Li_4SiO_3\;and\;Li_2O$ remains as interdependent, it may be expected that the composite exhibiting higher amount of irreversible capacity$(Li_2O)$ will deliver higher reversible capacity. In this study, pretreatment method of constant current-constant voltage (CC-CV) Provided high coulombic efficiency of SiO/C composite electrode removing the greater part of irreversible capacity.

• Journal of the Korean Electrochemical Society
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• v.11 no.1
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• pp.47-50
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• 2008

A new anode composition material comprising of SiO and Graphite has been prepared by adopting High energy ball milling (HEBM) technique. The anode material shows high initial charge and discharge capacity values of 1139 and 568 mAh/g, respectively. The electrode sustains reversible discharge capacity value of 719 mAh/g at 30th cycle with a high coulombic efficiency${\sim}99%$. Since the materials formed during initial charge process the nano silicon/$Li_4SiO_3$ and $Li_2O$ remains as interdependent, it may be expected that the composite exhibiting higher amount of irreversibility$(Li_2O)$ will deliver higher reversible capacity. In this study, constant current-constant voltage (CC-CV) charge method was employed in place of usual constant current (CC) method in order to convert efficiently all the SiO particles which resulted high initial discharge capacity at the first cycle. We improved considerably the initial discharge specific capacity of SiO/G composite by pretreatment(CC-CV).

• Bulletin of the Korean Chemical Society
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• v.32 no.11
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• pp.3952-3958
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• 2011

The effect of sintering temperature on the electrochemical property of $LiMn_2O_4$ was investigated. Results showed that the particle size was increased at higher sintering temperatures while the initial capacity was decreased after high temperature sintering. Capacity fading, on the other hand, was suppressed at lower sintering temperatures since the sintering at higher temperatures (${\geq}800^{\circ}C$) increased the Mn ions with a lower oxidation state ($Mn^{+3}$), which induced structural instability during cycling due to dissolution of Mn ions into the electrolyte. In particular, $LiMn_2O_4$ sintered above $830^{\circ}C$ showed severe capacity fading (capacity loss was 38% of initial capacity) by lower coulombic efficiency due to the abnormally increased particle size.

• Carbon letters
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• v.1 no.1
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• pp.36-40
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• 2000

The initial irreversible capacity (IIC) of a hard carbon during the charge/discharge reaction is strongly affected by both the initial irreversible capacity on the carbon surface $(IIC_S)$ and the initial irreversible lithium insertion into carbon $(IIC_B)$. The initial coulombic efficiency of the insertion and the desertion of lithium (IIE) can be used as a performance to classify $IIC_B$ of the carbon. The $IIC_B$ was proportional to the specific discharge capacity with a slope, $IIE^{-1}$ - 1. The IIE of hard carbon had four regions. $IIE_A$ for the region of 0~95 mAh/g of $Q_{D1}$ was 60.2%. $IIE_B$ and $IIE_C$ for the regions of 95~172 mAh/g and 172~308 mAh/g had 84.9% and 91.5%, respectively. $IIE_D$ was appeared above 308 mAh/g. But, the $IIE_D$ was reduced to 82.1% compared with $IIE_C$. These IIE might be corresponding to lithium desertion from carbon at the region of 0~172 mAh/g range, lithium desertion from the micropore of carbon at the region of 172~308 mAh/g range, and to the lithium stripping of the plated lithium for the region above 308 mAh/g, respectively.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.384-388
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• 2013

Fluorine-doping on the $Li_{1+x}Mn_{1.9-x}Al_{0.1}O_4$ spinel cathode materials is found to alter crystal shape, and enhance initial interfacial reactivity and solid electrolyte interphase (SEI) formation, leading to improved initial coulombic efficiency in the voltage region of 3.3-4.3 V vs. Li/$Li^+$ in the room temperature electrolyte of 1 M $LiPF_6$/EC:EMC. SEM imaging reveals that the facetting on higher surface energy plane of (101) is additionally developed at the edges of an octahedron that is predominantly grown with the most thermodynamically stable (111) plane, which enhances interfacial reactivity. Fluorine-doping also increases the amount of interfacially reactive $Mn^{3+}$ on both bulk and surface for charge neutrality. Enhanced interfacial reactivity by fluorine-doping attributes instant formation of a stable SEI layer and improved initial cyclic efficiency. The data contribute to a basic understanding of the impacts of composition on material properties and cycling behavior of spinel-based cathode materials for lithium-ion batteries.