• 한국전기화학회:학술대회논문집
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• 1999.11a
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• pp.83-91
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• 1999

Technical advances in manufacturing techniques and applied technologies have been made for bi cell manufacture, and are currently being implemented in the areas of discrete electrode / bi cell assembly, and electrode / separator lamination. Not only have improvements been noted in the reliability of the mechanical assembly and the increase in yields and decrease in costs, battery electrical performance has also been enhanced thru these assembly techniques. Evidence has been shown that the lamination techniques can influence porosity and electrolyte dispersion, and therefore electrical performance and long term reliability of the cells.

• Journal of the Korea Society of Computer and Information
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• v.19 no.2
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• pp.109-115
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• 2014

The research on solar energy that we get from nature to cope with energy exhaustion is a very significant and inevitable task for us to do. Along with this, lately, in Korea, as part of new growth engine industry regarding low-carbon green growth, we have selected the LED(Light Emitting Diode) as low power consuming, eco-friendly lighting equipment and have been facilitating research and development on it and creating a variety of new industries utilizing it. What was developed here in this research was the photovoltaic LED lighting system applying lithium polymer batteries equipped with the excellent performance of lithium ion batteries as well as significantly low explosive hazard. Its photovoltaic panel was made to have 100W capacity, and for its power supply system, functional convenience was considered so that it could be equipped with both DC and AC power to be used as household electricity in a variety of ways.

• Journal of the Korean Electrochemical Society
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• v.5 no.4
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• pp.197-201
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• 2002

In this study, a gel polymer electrolyte was prepared from urethane acrylate and its electrochemical performances were evaluated. And, $LiCoO_2/GPE/graphite$ cells were prepared and their performances depending on discharge currents and temperatures were evaluated. The precursor containing $5 vol\%$ curable mixture had a low viscosity relatively. Ionic conductivity of the gel polymer electrolyte at room temperature and $-20^{\circ}C$ was ca. $5.9\times10^{-3}S{\cdot}cm^{-1}\;and\;1.7\times10^{-3}S{\cdot}cm^{-1}$, respectively. GPE showed electrochemical stability up to potential of 4.5V vs. $Li/Li^+.LiCoO_2/GPE/graphite$ cell showed a good high-rate and a low-temperature performance.

• Journal of the Korean Electrochemical Society
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• v.13 no.4
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• pp.246-250
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• 2010

In this study, nano-crystallized $Al_2O_3$ was coated on the surface of $LiFePO_4$ powders via a novel dry coating method. The influence of coated $LiFePO_4$ upon electrochemical behavior was discussed. Surface morphology characterization was achieved by transmission electron microscopy (TEM), clearly showing nano-crystallized $Al_2O_3$ on $LiFePO_4$ surfaces. Furthermore, it revealed that the $Al_2O_3$-coated $LiFePO_4$ cathode exhibited a distinct surface morphology. It was also found that the $Al_2O_3$ coating reduces capacity fading especially at high charge/discharge rates. Results from the cyclic voltammogram measurements (2.5-4.2 V) showed a significant decrease in both interfacial resistance and cathode polarization. This behavior implies that $Al_2O_3$ can prevent structural change of $LiFePO_4$ or reaction with the electrolyte on cycling. In addition, the $Al_2O_3$ coated $LiFePO_4$ compound showed highly improved area-specific impedance (ASI), an important measure of battery performance. From the correlation between these characteristics of bare and coated $LiFePO_4$, the role of $Al_2O_3$ coating played on the electrochemical performance of $LiFePO_4$ was probed.

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.429-430
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• 2011

This paper presents a simple and cost-effective stand-alone rapid battery charging system of 30kW for electric vehicles. The proposed system mainly consists of active front-end rectifier of neutral point clamped 3-level type and non-isolated bi-directional dc-dc converter of multi-phase interleaved half-bridge topology with coupled inductors. The charging system is designed to operate for both lithium-polymer and lithium-ion batteries. The complete charging sequence is made up of three sub-interval operating modes; pre-charging mode, constant-current mode, and constant-voltage mode. The pre-charging mode employs the staircase shaped current profile to accomplish shorter charging time while maintaining the reliable operation of the battery. The proposed system is able to reach the full-charge state within less than 16min for the battery capacity of 8kWh by supplying the charging current of 67A. The optimal discharging algorithm for Vehicle to the Grid (V2G) operation has been adopted to maintain the discharging current of 1C. Owing to the simple and compact power conversion scheme, the proposed solution has superior module-friendly mechanical structure which is absolutely required to realize flexible power expansion capability in a very high-current rapid charging system.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.201-202
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• 2012

This paper presents a simple and cost-effective stand-alone rapid battery charging system of 30kW for electric vehicles. The proposed system mainly consists of active front-end rectifier of neutral point clamped 3-level type and non-isolated bi-directional dc-dc converter of multi-phase interleaved half-bridge topology. The charging system is designed to operate for both lithium-polymer and lithium-ion batteries. The complete charging sequence is made up of three sub-interval operating modes; pre-charging mode, constant-current mode, and constant-voltage mode. Each mode is operated according to battery states: voltage, current and State of Charging (SOC). The proposed system is able to reach the full-charge state within less than 16min for the battery capacity of 8kWh by supplying the charging current of 67A. The optimal discharging algorithm for Vehicle to the Grid (V2G) operation has been adopted to maintain the discharging current of 1C. Owing to the simple and compact power conversion scheme, the proposed solution has superior module-friendly mechanical structure which is absolutely required to realize flexible power expansion capability in a very high-current rapid charging system. Experiment waveforms confirm the proposed functionality of the charging system.

• Bulletin of the Korean Chemical Society
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• v.33 no.2
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• pp.608-612
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• 2012

We investigated the cycling behavior of $Li_4Ti_5O_{12}$ electrode in a cross-linked gel polymer electrolyte based on non-flammable ionic liquid consisting of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide and vinylene carbonate. The $Li_4Ti_5O_{12}$ electrodes in ionic liquid-based gel polymer electrolytes exhibited reversible cycling behavior with good capacity retention. Cycling data and electrochemical impedance spectroscopy analyses revealed that the optimum content of the cross-linking agent necessary to ensure both acceptable initial discharge capacity and good capacity retention was about 8 wt %.

• Journal of the Korean Electrochemical Society
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• v.15 no.4
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• pp.230-235
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• 2012

Polymer electrolytes consisted of $BF_3LiMA$ and 300 (PEGMA300) or 1100 (PEGMA1100) g $mol^{-1}$ of PEGMA were prepared and the electrochemical properties were characterized. Interestingly, the AC-impedance measurement shows $1.22{\times}10^{-5}S\;cm^{-1}$ of room temperature ionic conductivity from PEGMA1100 based solid polymer electrolytes while $8.54{\times}10^{-7}S\;cm^{-1}$ was observed in PEGMA300 based liquid polymer electrolytes. The more suitable coordination between lithium ion and ethylene oxide (EO) unit might be the reason of higher ionic conductivity which can be possible in PEGMA1100 based electrolytes since it has 23 EO units in monomer. The lithium ion transference number was found to be 0.6 due to the side reactions between $BF_3$ and lithium metal expecially for longer time but 0.9 was observed within 3000 seconds of measuring time which is strong evidence of a single-ion conductor.

• Journal of the Korean Electrochemical Society
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• v.15 no.2
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• pp.95-100
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• 2012

$LiFePO_4$ is an attractive cathode material due to its low cost, good cyclability and safety. But it has low ionic conductivity and working voltage impose a limitation on its application for commercial products. In order to solve these problems, the iron($Fe^{2+}$)site in $LiFePO_4$ can be substituted with other transition metal ions such as $Mn^{2+}$ in pursuance of increase the working voltage. Also, reducing the size of electrode materials to nanometer scale can improve the power density because of a larger electrode-electrolyte contact area and shorter diffusion lengths for Li ions in crystals. Therefore, we chose electrospinning as a general method to prepare $Li[Fe_{0.9}Mn_{0.1}]PO_4$ to increase the surface area. Also, there have been very a few reports on the synthesis of cathode materials by electrospinning method for Lithium ion batteries. The morphology and nanostructure of the obtained $Li[Fe_{0.9}Mn_{0.1}]PO_4$ nanofibers were characterized using scanning electron microscopy(SEM). X-ray diffraction(XRD) measurements were also carried out in order to determine the structure of $Li[Fe_{0.9}Mn_{0.1}]PO_4$ nanofibers. Electrochemical properties of $Li[Fe_{0.9}Mn_{0.1}]PO_4$ were investigated with charge/discharge measurements, electrochemical impedance spectroscopy measurements(EIS).

• Electrical & Electronic Materials
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• v.8 no.4
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• pp.487-494
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• 1995

The purpose of this study is to research and develop solid polymer electrolyte(SPE) for Li secondary battery. We investigated the effects of lithium salts, plasticizer addition, temperature dependence of conductivity and electrochemical stability window of polyethylene oxide(PEO) electrolytes. PEO electrolyte completed with LiCIO$\_$4/ shows the better conductivity than the others. PEO-LiCIO$\_$4/ electrolyte, when EO/Li$\^$+/ ratio is 8, showed adequate conductivity around room temperature. By adding propylene carbonate and ethylene carbonate to PEO-LiCIO$\_$4/ electrolyte, its conductivity was higher than that of PEO-LiCIO$\_$4/ without those. Also PEO$\_$8/LiCIO$\_$4/ electrolyte remains stable up to 4.5V vs. Li/Li.