• Journal of the Korean Ceramic Society
• /
• v.45 no.2
• /
• pp.112-118
• /
• 2008

To prepare the high-capacity cathode material with improved electrochemical performances, nanoparticles of $C0_3(PO_4)_2$ were coated on the powder surface of $Li[Co_{0.1}Ni_{0.15}Li_{0.2}Mn_{0.55}]O_2$, which was already synthesized by simple combustion method. The coated powders after the heat treatment at >$700^{\circ}C$ surely showed well-structured crystalline property with nanoscale surface coating layer, which was consisted of $LiCOPO_4$ phase formed from the reaction bwtween $CO_3(PO_4)_2$ and lithium impurities. In addition, cycle performance was particularly improved by the $CO_3(PO_4)_2$-coating for the cathode material for lithium rechargeable batteries.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2010.06a
• /
• pp.248-248
• /
• 2010

리튬이온 2차전지의 대체 양극 후보 물질인 $LiFePO_4$를 합성하기 위하여 출발원료로 $Li_2CO_3$, $Fe_2O_3$, $NH_4H_2PO_4$를 사용하여 볼밀 방법으로 혼합 분쇄한 후 열처리를 실시하였다. 합성 시에 3가 Fe를 2가로 환원시키기 위하여 $C_{12}H_{22}O_{11}$(흑설탕)을 출발원료와 함께 5 ~ 12 wt%로 나눠서 첨가하였다. 합성 후 XRD로 결정구조의 양질성을 확인하였고. FE-SEM으로 나노미터 크기의 구형 입자를 관찰하였다. XRF를 이용하여 3 ~ 10 wt%의 탄소 잔량을 확인하였다. 전기화학적 특성을 충 방전시험기로 평가한 결과, 8wt%의 탄소원을 첨가한 $LiFePO_4$에서 가장 좋은 수명 특성을 얻었고, 최대 145 mAh/g의 방전용량을 얻었다.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.2
• /
• pp.536-540
• /
• 2011

This study reports the origin of the electrochemical improvement of $LiFePO_4$ when synthesized by wet milling using acetone without conventional carbon coating. The wet milled $LiFePO_4$ delivers 149 $mAhg^{-1}$ at 0.1 C, which is comparable to carbon coated $LiFePO_4$ and approximately 74% higher than that of dry milled $LiFePO_4$, suggesting that the wet milling process can increase the capacity in addition to conventional carbon coating methods. UV spectroscopy, elemental microanalysis, and evolved gas analysis are used to find the root cause of the capacity improvement during the mechanochemical reaction in acetone. The analytical results show that the improvement is attributed to the conductive residual carbon on the surface of the wet milled $LiFePO_4$ particles, which is produced by the reaction of $FeC_2O_4{\cdot}2H_2O$ with acetone during wet milling through oxygen deficiency in the precursor.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.1
• /
• pp.79-88
• /
• 2013

$LiFePO_4$ is a promising active material (AM) suitable for use in high performance lithium-ion batteries used in automotive applications that require high current capabilities and a high degree of safety and reliability. In this study, an optimization of the electrode design parameters was performed to produce high capacity lithium-ion batteries based on $LiFePO_4$/graphite electrodes. The electrode thickness and porosity (AM density) are the two most important design parameters influencing the cell capacity. We quantified the effects of cathode thickness and porosity ($LiFePO_4$ electrode) on cell performance using a detailed one-dimensional electrochemical model. In addition, the effects of those parameters were experimentally studied through various coin cell tests. Based on the numerical and experimental results, the optimal ranges for the electrode thickness and porosity were determined to maximize the cell capacity of the $LiFePO_4$/graphite lithium-ion batteries.

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

• Journal of the Korean Electrochemical Society
• /
• v.17 no.4
• /
• pp.229-236
• /
• 2014

In this study, the method to improve the electrochemical performance of $LiFePO_4$ by carbon coating and morphology control into porous structure was studied. The synthesis of $LiFePO_4$ was done by coprecipitation method by two step procedure. In the first step $FePO_4$ precursor was synthesized by coprecipitation method, followed by impregnation of lithium into the precursor at $750^{\circ}C$. The carbon coating was done by both physical and chemical coating processes. Using the physical coating process, the amount of coating layer was 6% and the capacity achieved was 125 mAh/g. In case of chemical coating process, the active material delivered 130~140 mAh/g, which is about 40% improvement of delivered capacity compared to uncoated $LiFePO_4$. For the morphology control into porous structure, we added nano particles of $Al_2O_3$ or $SiO_2$ into the active materials and formed the nanocomposite of ($Al_2O_3$ or $SiO_2$)/$LiFePO_4$. Between them, $SiO_2/LiFePO_4$ porous nanocomposite showed larger capacity of 132 mAh/g.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.3
• /
• pp.852-856
• /
• 2011

The lithium ion diffusion coefficients of bare, carbon-coated and Cr-doped $LiFePO_4$ were obtained by fitting the discharge curves of each half cell with Li metal anode. Diffusion losses at discharge curves were acquired with experiment data and fitted to equations. Theoretically fitted equations showed good agreement with experimental results. Moreover, theoretical equations are able to predict lithium diffusion coefficient and discharge curves at various discharge rates. The obtained diffusion coefficients were similar to the true diffusion coefficient of phase transformation electrodes. Lithium ion diffusion is one of main factors that determine voltage drop in a half cell with $LiFePO_4$ cathode and Li metal anode. The high diffusion coefficient of carbon-coated and Cr-doped $LiFePO_4$ resulted in better performance at the discharge process. The performance at high discharge rate was improved much as diffusion coefficient increased.

• Journal of the Korean Magnetics Society
• /
• v.22 no.1
• /
• pp.15-18
• /
• 2012

The olivine structured $LiFe_{0.9}Mn_{0.1}PO_4$ material was prepared by solid state method, and was analyzed by x-ray diffractometer (XRD), superconducting quantum interference devices (SQUID) and Mossbauer spectroscopy. The crystal structure of $LiFe_{0.9}Mn_{0.1}PO_4$ was determined to be orthorhombic (space group: Pnma) by Rietveld refinement method. The value of N$\acute{e}$el temperature ($T_N$) for $LiFe_{0.9}Mn_{0.1}PO_4$ was determined 50 K. The temperature dependence of the magnetization curves showed magnetic phase transition from paramagnetic to antiferromagnetic at $T_N$ by SQUID measurement. M$\ddot{o}$ssbauer spectra of $LiFe_{0.9}Mn_{0.1}PO_4$ showed 2 absorption lines at temperatures above $T_N$ and showed asymmetric 8 absorption lines at temperatures below $T_N$. These spectra occurred due to the magnetic dipole and electric quardrupole interaction caused by strong crystalline field at asymmetric $FeO_6$ octahedral sites.

• Journal of Electrical Engineering and Technology
• /
• v.13 no.1
• /
• pp.413-417
• /
• 2018

The $Li_4Ti_5O_{12}$ of anode material for the hybrid capacitor was coated using $CePO_4$, $M_3(PO_4)_2$ (M=Mg, Zn). The capacitance of phosphate coated $Li_4Ti_5O_{12}$ was found to be lower than that of $Li_4Ti_5O_{12}$, whereas the equivalent series resistance was higher than that of $Li_4Ti_5O_{12}$. With an increase in cycle number, the base of cylindrical cell exhibited swelling due to gas generated from the reaction between $Li_4Ti_5O_{12}$ and electrolyte. The swelling cycle number of phosphate coated $Li_4Ti_5O_{12}$ was higher than that of $Li_4Ti_5O_{12}$ due to improvement in electrochemical stability. Based on the results, it is proposed that phosphate coating can be employed as a barrier layer to control the gassing reaction by isolating the $Li_4Ti_5O_{12}$ particle from electrolyte solution.

• Journal of IKEEE
• /
• v.26 no.2
• /
• pp.232-239
• /
• 2022

We analyzed the effect of post-annealing on lithium phosphate (Li₃PO₄) solid-state thin-film. Li₃PO₄ thin films were deposited by radio frequency (RF) sputtering, with subsequent annealing of the films at 200-400 ℃. SEM imaging of the sample surfaces showed no significant difference in morphology between the annealed and non-annealed samples. XRD analysis indicated that the samples consist of an amorphous-like structure. Post-annealing changes in binding energy were confirmed by XPS analysis, while the leakage current density at -6 V was measured to be about 7.15 times lower in a device that had been annealed at 400 ℃ vs a non-annealed device. It was confirmed that the leakage current decreased with increasing post-annealing temperature.