• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.433-436
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• 2013

Carbon-coated $Li_3V_2(PO_4)_3-LiMnPO_4$ composite cathode materials are first reported in this work, prepared by the mechanochemical process with a complex metal oxide as the precursor and sucrose as the carbon source. X-ray diffraction pattern of the composite material indicates that both olivine $LiMnPO_4$ and monoclinic $Li_3V_2(PO_4)_3$ co-exist. We further investigated the electrochemical properties of our $Li_3V_2(PO_4)_3-LiMnPO_4$ composite cathode materials using galvanostatic charging/discharging tests, where our $Li_3V_2(PO_4)_3-LiMnPO_4$ composite electrode materials exhibit the charge/discharge efficiency of 91.9%, while $Li_3V_2(PO_4)_3$ and $LiMnPO_4$ exhibit the efficiency of 87.7 and 86.7% in the first cycle. The composites display unique electrochemical performances in terms of overvoltage and cycle stability, displaying a reduced gap of 141.6 mV between charge and discharge voltage and 95.0% capacity efficiency after $15^{th}$ cycles.

• Journal of the Korean Electrochemical Society
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• v.15 no.2
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• pp.101-108
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• 2012

The purpose of this study was to improve the conductivity of $Li_3V_2(PO_4){_3}$ by adding carbon source so that the discharge rate and cyclic properties were improved. Glucose and CNT were added to $Li_3V_2(PO_4){_3}$ and the structure and electrochemical properties were studied. $Li_3V_2(PO_4){_3}$, $Li_3V_2(PO_4){_3}$/C and $Li_3V_2(PO_4){_3}$/CNT were synthesised by solid state reaction using hydrogen reduction method at 600, 700, 800, $900^{\circ}C$. The cathode materials were assembled to coin cell type 2032 with Lithium metal as a counter electrode. The coin cell was galvanostatically evaluated in the voltage range of 3.0~4.8 V.

• 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.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.137.1-137.1
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• 2011

올리빈 구조의 $LiFePO_4$ 정극 활물질은 $650^{\circ}C$에서 고상법으로 제조되었다. $LiFePO_4$의 전자전도도를 향상시키기 위하여 graphite nanofiber(GNF)를 각각 3wt%, 5wt%, 7wt%, 9wt% 첨가하여 $LiFePO_4$-C를 제조하였다. 제조된 분말의 입자 형태를 확인하기 위하여 X-ray diffraction(XRD)과 File Electronic Scaning Electromicroscopy(FE-SEM)를 측정하였다. XRD결과로부터 제조된 분말은 모두 순수한 결정 구조를 나타내었고 입자의 크기는 약 200nm였다. 5wt% GNF를 첨가한 $LiFePO_4$-C는 기타 첨가량에 비해 방전용량이 가장 높았다. 첫 사이클의 용량은 151.73mAh/g 나타났고 50 사이클 뒤에도 92% 이상을 유지하고 있었다. 첨가하지 않은 것에 비해 43% 증가하였다. $LiFePO_4$-C(3wt%), $LiFePO_4$-C(7wt%), $LiFePO_4$-C(9wt%)의 첫 사이클 방전용량은 각각 147.94mAh/g, 136.64mAh/g, 121.07mAh/g 나타났다. $LiFePO_4$-C(5wt%)에 비해 용량은 떨어쪘지만 순수한 $LiFePO_4$보다 많이 높았다. 임피던스 결과를 보면 기타 첨가량에 비해 $LiFePO_4$-C(5wt%)의 저항 제일 낮았다. 이는 충방전 결과와 일치하였다. graphite nanofiber의 첨가로 인하여 $LiFePO_4$ 정극 활물질의 전자전도도가 높아지고, 따라서 전기화학적 특성도 크게 향상되었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.368-369
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• 2006

The pure $LiFePO_4$, carbon added $LiFePO_4(LiFePO_4/C$) and pyrene added $LiFePO_4(LiFePO_4/P$) are synthesized by using solid-state reaction. XRD patterns show no impurity phase in the three kinds of the cathode materials. The 10wt% pyrene added $LiFePO_4$ shows around 140mAh/g of discharge capacity at 3rd cycle compared to the pure $LiFePO_4$. The carbon added $LiFePO_4$ shows 145mAh/g of discharge capacity at 3rd cycle and stable cycle-life compared to the others.

• Bulletin of the Korean Chemical Society
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• v.32 no.5
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• pp.1491-1494
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• 2011

Lithium vanadium phosphate, $Li_3V_2(PO_4)_3$ was prepared by a simple solid state route. It was found that making a fine powder of $Li_3V_2(PO_4)_3$ by the mechanical milling is very effective for increasing the insertion/extraction of lithium from $Li_3V_2(PO_4)_3$ structure. In charge/discharge test, the ball-milled $Li_3V_2(PO_4)_3$ sample exhibited a higher initial discharge capacity of 174 mAh/g in the voltage range of 3.0-4.8 V, compared with pure $Li_3V_2(PO_4)_3$ sample (152 mAh/g). Furthermore, the ball-milled $Li_3V_2(PO_4)_3$ presented not only higher cycle retention rate after 50 cycles, but also better rate capability compared with pure sample in the whole region (0.1-7 C).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.132-132
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• 2009

Phospho-olivine $LiFePO_4$ cathode materials were prepared by hydrothermal reaction. In this study, Multi-walled carbon nanotube (MWCNT) and Carbon black was added to enhance the electrical conductivity of $LiFePO_4$. $LiFePO_4$, $LiFePO_4$-MWCNT and $LiFePO_4$-C particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) transmission electron microscope (TEM). $LiFePO_4/SPE/Li$, $LiFePO_4$-MWCMT/SPE/Li and $LiFePO_4$-C/SPE/Li cells were characterized electrochemically by charge/discharge experiments at a constant current density of $0.1mA\;cm^{-2}$ in a range between 2.5 and 4.3 V vs. $Li/Li^+$ and cyclic voltammetry (CV).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.133-133
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• 2009

Phospho-olivine $LiFePO_4$ and $LiTi_{0.1}Fe_{0.9}PO_4$ cathode materials were prepared by the solid-state reaction. To improve conductivity we carried out electrochemical performance of $Ti^{2+}$ doped $LiFePO_4$. The $Ti^{2+}$ doped $LiFePO_4$ started 3.36 V of flat voltage on discharge curve and showed a gentle decline in the curve compared to undoped $LiFePO_4$ without great changes of capacity. And so, we could achieve to improve electrochemical performance as reversible, cycle life. Similarly, $LiFePO_4$ doping with $Ti^{2+}$ was showed the effect of dopant which was obtained the improved discharge capacity as 140 mAh/g and good cycling performance.

• Bulletin of the Korean Chemical Society
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• v.32 no.3
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• pp.836-840
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• 2011

This study examines the effects of a carbon coating on the electrochemical performances of $LiFePO_4$. The results show that the capacity of bare $LiFePO_4$ decreased sharply, whereas the $LiFePO_4$/C shows a well maintained initial capacity. The Li ion diffusivity of the bare and carbon coated $LiFePO_4$ is calculated using cyclic voltammetry (CV) to determine the correlation between the electrochemical performance of $LiFePO_4$ and Li diffusion. The diffusion constants for $LiFePO_4$ and $LiFePO_4$/C measured from CV are $6.56{\times}10^{-16}$ and $2.48{\times}10^{-15}\;cm^2\;s^{-1}$, respectively, indicating considerable increases in diffusivity after modifications. The Li ion diffusivity (DLi) values as a function of the lithium content in the cathode are estimated by electrochemical impedance spectroscopy (EIS). The effects of the carbon coating as well as the mechanisms for the improved electrochemical performances after modification are discussed based on the diffusivity data.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.5
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• pp.167-173
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• 2023

Li₃V₂(PO₄)₃ and Li₃V₂(PO₄)₃/C composite with single phase monoclinic structure for the cathode materials are successfully synthesized by direct co-precipitation method using N₂H₄·H₂O as the reducing agent and alginic acid as the carbon source, and their electrochemical properties were compared. The particles with approximately 1~2 ㎛ size and the uniform spherical-like morphology of the narrow particle size distribution were obtained. In addition, the residual carbon can also improve the electrical conductivity. The Li₃V₂(PO₄)₃/C composite has improved initial specific discharge capacity and excellent cycle characteristics to maintain capacity stably than Li₃V₂(PO₄)₃. The results indicate that the reducing agent and carbon composite can affect the good crystallinity and electrochemical performance of the cathode materials.