• Journal of the Korean Electrochemical Society
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• v.11 no.4
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• pp.268-272
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• 2008

$LiFePO_4$ material was synthesized by electrospinning method to obtain optimal particle size($50{\sim}100\;nm$) without carbon coating or ball milling. This material showed an orthorthombic structure with Pnma space group without any impurities, such as FeP or $Fe_2P$, in the XRD pattern. The particle morphology and particle shape were observed by SEM analysis. Li/$LiFePO_4$ cell showed a high initial discharge capacity of 135 mAh/g, at current density of $0.1\;mA/cm^2$ with a cut-off voltage of 2.8 to 4.0V. This cell exhibited a perfect cycle performance over 99.9% cycle retention rate up to 50 cycles.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.316-316
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• 2007

리튬폴리머 전지용 정극활물질인 $LiFePO_4$를 수열법으로 합성하였다. 제조한 정극활물질 $LiFePO_4$는 X-ray 회절분석을 통하여 olivine 구조임을 확인하였다. 전극 제조 시 첨가된 도전재의 종류에 따른 전기화학적 특성변화를 알기 위하여, Acetylene Black, Super-Black, Multi-Walled Carbon Nanotube(MWCNT), SP270을 도전재로 제조된 정극활물질과 PVDF를 결합제로 사용하였다. 셀은 제조된 정극과 고체전해질 $25PVDFLiCIO_4EC_{10}PC_{10}$를 사용하고, 부극은 금속리튬으로 coin 타입의 cell을 조립하여 충방전을 진행하였다. 충방전 진행결과, Multi-Walled Carbon Nanotube(MWCNT)를 도전재로 사용하였을 경우, 초기 방전용량은 94mAh/g, 100cycle 후에는 약 93mAh/g인 기타 도전재를 사용하였을 때보다 안정하고 높은 방전용량을 나타내었다. 이때의 충방전 전류밀도는 0.1mAh/g이고 전압범위 는 2.5~4.3V이었다.

• Journal of Electrochemical Science and Technology
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• v.3 no.3
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• pp.135-142
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• 2012

Over the past few years, $LiFePO_4$ has been actively studied as a cathode material for lithium-ion batteries because of its advantageous properties such as high theoretical capacity, good cycle life, and high thermal stability. However, it does not have a very good power capability owing to the low lithium-ion diffusivity and poor electronic conductivity. Reduction in particle size of $LiFePO_4$ to the scale of nanometers has been found to dramatically enhance the above properties, according to many earlier reports. However, because of the intrinsically low tap density of nanomaterials, it is difficult to commercialize this method. Many studies are being carried out to improve the volumetric energy density of this material and many methods have been reported so far. This paper provides a brief summary of the synthesis methods and electrochemical performances of micro-spherical $LiFePO_4$ having high volumetric energy density.

• Journal of Electrochemical Science and Technology
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• v.2 no.2
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• pp.103-109
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• 2011

Nanocrystalline $LiFePO_4$ powders were prepared at 660-$670^{\circ}C$ in an Ar atmosphere using two different synthetic routes, solid-state and sol-gel. Both materials showed well-developed XRD patterns without any impurity peaks. Particles composed in the range of 200-300 nm from the solid-state method, and 50-100 nm from the sol-gel method, were confirmed through scanning electron microscopy and dynamic light scattering. The $LiFePO_4$ obtained by the sol-gel method offered a high discharge capacity (153 mAh/g) and stable discharge behavior, even at elevated temperatures (50 and $60^{\circ}C$), whereas poor electrochemical performance was observed from the solid-state method. Rate capability studies for sol gel-derived $LiFePO_4$ ranged from 0.2 to 30 C, which revealed excellent retention over 70 cycles with a 99.9% capacity.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.397-398
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• 2015

본 논문은 $LiFePO_4$ 셀의 SOC(State of Charge) 추정에서 가장 중요한 역할을 하는 모델 파라미터인 OCV(Open Circuit Voltage)의 설계에 관한 것이다. $LiFePO_4$ 셀은 히스테리시스 특성 때문에 Charging/Discharging OCV값을 이은 curve인 Major loop만으로는 신뢰도 높은 SOC 추정이 어렵다. 따라서, 기존의 Major loop에 추가적으로 SOC 10% 구간별로 Minor loop을 설계해 줌으로써 배터리 모델링의 정확도를 높이고, 이를 최종적으로 EKF(Extended Kalman Filter)알고리즘을 이용하여 SOC 추정으로 해봄으로써 정확도 향상을 비교해 보고 분석해 보고자 한다.

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.304-307
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• 2012

Nano-fibers of LiFePO4 were synthesized from a metal oxide precursor by adopting electrospinning method. After calcination of the above precursor nano-fibers at 800 ℃, LiFePO4 nano-fibers with a diameter of 300 ~ 800 nm, were successfully obtained. Measurement were performed using X-ray diffraction (XRD), fourier transform infrared spectrometer (FT-IR), videoscope, scanning electron microscope (SEM) and atomic force microscope (AFM), respectively, were performed to characterize the properties of the as-prepared materials. The results showed that the crystalline phase and morphology of the fibers were largely influenced the starting materials and electrospinning conditions.

• Journal of the Korean Ceramic Society
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• v.43 no.2 s.285
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• pp.121-125
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• 2006

[ $LiFePO_4$ ] is one of the promising materials for cathode material of secondary lithium batteries due to its high energy density, low cost, environmental friendliness and safety. $LiFePO_4$ was synthesized by the solid-state reaction method at 500 - 800°C. The crystal structure of $LiFePO_4$ was analyzed by X-ray powder diffraction. The samples synthesized at 600 and $700^{\circ}C$ showed a single phase of a olivine structure. The particle sizes were increased and the specific surface areas were decreased with heating temperatures. The electrochemical performance was investigated by coin cell test. The discharge capacities at 0.1 C-rate were 118 mAh/g and 112 mAh/g at $600^{\circ}C,\;700^{\circ}C$, respectively. In an attempt to improve the electrical conductivity of cathode materials, $LiFePO_4/graphite$ composite was prepared with various graphite contents. The electrical conductivity and discharge capacity were increased with increasing the graphite contents in composite samples. The rate capabilities at high current densities were also improved.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.121.1-121
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• 2003

• Journal of the Mineralogical Society of Korea
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• v.22 no.1
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• pp.63-72
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• 2009

Carbon-coated lithium iron phosphate ($LiFePO_4/C$) composites are synthesized by the modified mechanical activation method (modified MA process) and studied by the Rietveld structural refinement. Rietveld indices of $LiFePO_4/C$ indicate good fitting with $R_p=8.14%,\;R_{wp}=11.1%,\;R_{exp}=9.09%,\;R_B=3.88%$, and S (GofF, Goodness of fit) = 1.2, respectively. $LiFePO_4/C$ with a space group Pnma shows a = 10.3229(3)${\AA}$, b = 6.0052(2) ${\AA}$, c = 4.6939(1) ${\AA}$, and V = 290.98(1) ${\AA}^3$ in dimension, indicating good agreements with those of previous works. Synthetic powders are nano-sized ($65{\sim}90nm$) homogeneous particles with high purity. Thus the modified MA method will be an efficient process to get a high quality cathode material for commercial lithium batteries.

• Journal of the Korean Electrochemical Society
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• v.24 no.3
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• pp.52-64
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• 2021

The effect of Fe and BO₃ doping on structure, thermal, and electrical properties of Li_1+xFe_xTi_2-x(PO₄)_3-y(BO₃)_y (x = 0.2, 0.5)-based glass and glass ceramics was investigated. In addition, their crystallization behavior during sintering and ionic conductivity were also investigated in terms of sintering temperature. FT-IR and XPS results indicated that Fe²⁺ and Fe³⁺ ions in Li_1+xFe_xTi_2-x(PO₄)_3-y(BO₃)_y glass worked as a network modifier (FeO₆ octahedra) and also as a network former (FeO₄ tetrahedra). In the case of the glass with low substitution of BO₃, boron formed (PB)O₄ network structure, while boron preferred BO₃ triangles or B₃O₃ boroxol rings with increasing the BO₃ content owing to boic oxide anomaly, which can result in an increased non-bridging oxygen. The glass transition temperature (GTT) and crystallization temperature (CT) was lowered as the BO₃ substitution was increased, while Fe²⁺ lowered the GTT and raised the CT. The ionic conductivity of Li_1+xFe_xTi_2-x(PO₄)_3-y(BO₃)_y glass ceramics were 8.85×10^-4 and 1.38×10^-4S/cm for x = 0.2 and 0.5, respectively. The oxidation state of doped Fe and boric oxide anomaly were due to the enhanced lithium ion conductivity of glass ceramics.