• Korean Chemical Engineering Research
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• v.57 no.4
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• pp.547-552
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• 2019

Electrochemical properties of $LiMn_{0.8}Fe_{0.2}PO_4$ cathode were investigated with gel polymer electrolyte (GPE). To access fast and efficient transport of ions and electrons during the charge/discharge process, a pure and well-crystallized $LiMn_{0.8}Fe_{0.2}PO_4$ cathode material was directly synthesized via spray-pyrolysis method. For high operation voltage, polyacrylonitrile (PAN)-based gel polymer electrolyte was then prepared by electrospinning process. The gel polymer electrolyte showed high ionic conductivity of $2.9{\times}10^{-3}S\;cm^{-1}$ at $25^{\circ}C$ and good electrochemical stability. $Li/GEP/LiMn_{0.8}Fe_{0.2}PO_4$ cell delivered a discharge capacity of $159mAh\;g^{-1}$ at 0.1 C rate that was close to the theoretical value ($170mAh\;g^{-1}$). The cell allows stable cycle performance (99.3% capacity retention) with discharge capacity of $133.5mAh\;g^{-1}$ for over 300 cycles at 1 C rate and exhibits high rate-capability. PAN-based gel polymer is a suitable electrolyte for application in $LiMn_{0.8}Fe_{0.2}PO_4/Li$ batteries with perspective in high energy density and safety.

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.191-195
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• 2011

This study reports the root cause of the improved rate performance of $LiFePO_4$ after Cr doping. By measuring the chemical diffusion coefficient of lithium ($D_{Li}$) using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the correlation between the electrochemical performance of $LiFePO_4$ and Li diffusion is acquired. The diffusion constants for $LiFePO_4$/C and $LiFe_{0.97}Cr_{0.03}PO_4$/C measured from CV are $2.48{\times}10^{-15}$ and $4.02{\times}10^{-15}cm^2s^{-1}$, respectively, indicating significant increases in diffusivity after the modification. The difference in diffusivity is also confirmed by EIS and the $D_{Li}$ values obtained as a function of the lithium content in the cathode. These results suggest that Cr doping facilitates Li ion diffusion during the charge-discharge cycles. The low diffusivity of the $LiFePO_4$/C leads to the considerable capacity decline at high discharge rates, while high diffusivity of the $LiFe_{0.97}Cr_{0.03}PO_4$/C maintains the initial capacity, even at high C-rates.

• Transactions on Electrical and Electronic Materials
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• v.15 no.6
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• pp.320-323
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• 2014

Ga-doped $LiFePO_4$ cathode materials were synthesized using a hydrothermal method. The microstructural characteristics and electrochemical performances were systematically investigated using field emission scanning electron microscopy, high-resolution X-ray diffraction, energy dispersive X-ray spectroscopy, charge-discharge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. Among the as-prepared samples, $LiFe_{0.96}Ga_{0.04}PO_4$ demonstrates the best electrochemical properties in terms of discharge capacity, electrochemical reversibility, and cycling performance with an initial discharge capacity of $125mAh\;g^{-1}$ and high lithium ion diffusion coefficient of $1.38{\times}10^{-14}cm^2s^{-1}$ (whereas for $LiFePO_4$, these were $113mAh\;g^{-1}$ and $8.09{\times}10^{-15}cm^2\;s^{-1}$, respectively). The improved electrochemical performance can be attributed to the facilitation of Li+ ion effective diffusion induced by $Ga^{3+}$ substitution.

• Journal of the Korean Electrochemical Society
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• v.15 no.1
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• pp.27-34
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• 2012

$Li_3V_2(PO_4)_3$/carbon composite materials are synthesized from a sucrose-containing precursor. Amorphous $Li_3V_2(PO_4)_3/C$ (a-LVP/C) and crystalline $Li_3V_2(PO_4)_3/C$ (c-LVP/C) are obtained by calcining at $600^{\circ}C$ and $800^{\circ}C$, respectrively, and electrochemical performance as the negative electrode for lithium secondary batteries is compared for two samples. The a-LVP electrode shows much larger reversible capacity than c-LVP, which is ascribed to the spatial $Li^+$ channels and flexible structure of amorphous material. In addition, this electrode shows an excellent rate capability, which can be accounted for by the facilitated $Li^+$ diffusion through the defect sites. The sloping voltage profile is another advantageous feature for easy SOC (state of charge) estimation.

• 한국전기화학회:학술대회논문집
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• 2004.04a
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• pp.20-20
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• 2004

• Journal of Electrochemical Science and Technology
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• v.3 no.4
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• pp.172-177
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• 2012

Mo-doped $LiFePO_4$ was synthesized via co-precipitation method using sucrose as the carbon source. Structure, surface morphology, and the electrochemical properties of the synthesized olivine compounds were investigated using Rietveld refinement of X-ray diffraction data (XRD), scanning electron microscopy (SEM), and electrochemical charge-ischarge tests. Spherical morphology with the particle size of ${\sim}8{\mu}m$ authenticated the enhanced tap density and volumetric energy density of the synthesized materials. Charge-discharge behavior of $LiFePO_4$ and Mo-doped $LiFePO_4$ cells demonstrated a specific capacity of 130 and 145 mAh $g^{-1}$, respectively. Mo-doped $LiFePO_4$ cells exhibited an excellent discharge capacity at 96 mAh $g^{-1}$ at 7 C-rate.

• Bulletin of the Korean Chemical Society
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• v.35 no.10
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• pp.2901-2905
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• 2014

The hierarchical-structured $LiFePO_4$ cathode materials were synthesized by one-step microwave synthesis, and their electrochemical properties were investigated. Addition of citric acid during the reaction lead to the formation of hierarchical structured $LiFePO_4$, which has both nano- and micron-characteristics advantageous for energy density and electrode fabrication. Adjusting the molar ratio of Fe to citric acid enhanced the electrochemical properties of $LiFePO_4$.

• Korean Chemical Engineering Research
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• v.55 no.2
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• pp.242-246
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• 2017

The application of composite cathode materials including $LiFePO_4$ (lithium iron phosphate) of olivine crystal structure, which has high thermal stability, were investigated as alternatives for hybrid battery-capacitors with a $LiMn_2O_4$ (spinel crystal structure) cathode, which exhibits decreased performance at high temperatures due to Mn-dissolution. However, these composite cathode materials have been shown to have a reduction in capacity by conducting life cycle experiments in which a $LiFePO_4$/activated carbon cell was charged and discharged between 1.0 V and 2.3 V at two temperatures, $25^{\circ}C$ and $60^{\circ}C$, which caused a degradation of the anode due to the lowered voltage in the anode. To avoid the degradation of the anode, composite cathodes of $LiFePO_4/LiMn_2O_4$ (50:50 wt%), $LiFePO_4$/activated carbon (50:50 wt%) and $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ (50:50 wt%) were prepared and the life cycle experiments were conducted on these cells. The composite cathode including $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ of layered crystal structure showed stable voltage behavior. The discharge capacity retention ratio of $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ was about twice as high as that of a $LiFePO_4/LiMn_2O_4$ cell at thermal stability experiment for a duration of 1,000 hours charged at 2.3 V and a temperature of $80^{\circ}C$.

• Journal of Advanced Engineering and Technology
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• v.6 no.2
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• pp.125-129
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• 2013

In the pyrochemcial process of spent nuclear fuel, it is necessary to separate rare earth nuclides from LiCl-KCl eutectic waste salt for radioactive waste reduction. This paper presents the phosphorylation of neodymium chloride in LiCl-KCl-NdCl₃ system using Li₃PO₄-K₃PO₄ as a phosphorylation agent in a chemical reactor with pitched blade impellers. The phosphorylation test was performed changing operation temperature, stirring rate, and amount of phosphorylation agent. Neodymium chloride was effectively converted into neodymium phosphate (NdPO₄). It was confirmed that more than 99 wt% of neodymium can be separated from LiCl-KCl-NdCl₃ system using a phosphorylation method l

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.279-279
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• 2009

$LiFePO_4$는 낮은 전기전도도로 인하여 전이금속의 도핑과 카본코팅으로 전기화학적 특성을 향상시키려는 연구가 많이 되어 왔다. 또한 다양한 합성법으로 $LiFePO_4$의 입자사이즈를 최적화 하기 위해 많은 연구가 진행중이다. 특히 고상 합성법은 결정의 미세화가 가능하고, 상온에서 쉽고 용이하게 원소간의 합금화 및 화학반응을 유도하는 등의 장점으로 인해 가장 널리 사용하고 있는 합성법중 하나이다. 이번 연구에서도 고상합성법을 사용하여 $LiFePO_4$를 합성했으며, 카본소스로서 카르복시산등의 유기산을 사용하여 코팅을 시도해 보았다. 이렇게 합성된 $LiFePO_4$의 물리적 측정을 통하여 입사의 형상 및 크기를 관찰하였고, 하프셀을 구성하여 전기화학적 특성을 확인하였다.