Electrochemical Characteristics of LiFePO4 with Conductivity Materials for Lithium Polymer Batteries

( En Mei Kim ),( Kyung Hee Park ),( Hal Bod Gu ) 조선대학교 공학기술연구원 2008 공학기술논문지 Vol.1 No.1

Phospho-olivine LiFePO4 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 LiFePO4. LiFePO4, LiFePO4-MWCNT and LiFePO4-C particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) transmission electron microscope (TEM). LiFePO4/SPF/Li, LiFePO4-MWCMT/SPF/Li and LiFePO4-C/SPE/Li cells were characterized electrochemically by charge/discharge experiments at a constant current density of 0.1 mA cm(-2) in a range between 2.5 and 4.3 V vs. Li/Li(+) and cyclic voltammetry (CV). The results showed that initial discharge capacity of LiFePO4 was 103 mA h g(-1). The discharge capacity of LiFePO4-MWCNT/SPF/Li cell with 5 wt % MWCNT was 124 mAh g(-), LiFePO4-C/SPE/Li cell with 5 wt % carbon black was 128 mAh g(-1) at the first cycle.

LiFePO₄와 Li₄P₂O₇의 ⁷Li MAS NMR 특성 연구

한덕영,박남신,이상혁,이학만,김창삼,Han, Doug-Young,Park, Nam-Sin,Lee, Sang-Hyuk,Lee, Hak-Man,Kim, Chang-Sam 한국결정성장학회 2011 한국결정성장학회지 Vol.21 No.1

[ $^7Li$ ]Magic Angle Spinning(MAS) NMR Spectroscopy를 활용하여 $Li_4P_2O_7$와 $LiFePO_4$ 물질에서 $^7Li$ 핵의 NMR 특성 및 화합물 분자내의 국부적 구조 연구를 수행하였다. $Li_4P_2O_7$와 $LiFePO_4$ 물질 연구는 리튬이온전지에서 고체-전해질 경계상(SEI, solid-electrolyte interphase) 물질 연구를 위한 것이다. $Li_4P_2O_7$와 $LiFePO_4$ 분말은 고상합성법으로 제조하였다.$^7Li$MAS NMR 실험은 $27^{\circ}C$에서 $97^{\circ}C$의 영역에서 변온 실험을 수행하였으며 이는 주변 온도 변화 환경에서 $Li_4P_2O_7$ 물질 내의 Li 핵의 구조 변화를 관찰하기 위한 것이다. $^7Li$ MAS NMR 측정 결과 시료 온도가 $27^{\circ}C$에서 $97^{\circ}C$의 온도 분포 영역에서는 $Li_4P_2O_7$ 물질 내부의 Li 핵은 구조적으로 변화하지 않는 것이 확인되었다. 금번 실험을 통하여 $LiFePO_4$ 분말에 5.0 wt%이내로 포함되어있는 $Li_4P_2O_7$ 물질의 $^7Li$ MAS NMR 신호를 측정할 수 있는 측정 조건을 알았다. [ $^7Li$ ]Magic Angle Spinning (MAS) NMR spectroscopy has been used to study the lithium local environments in $Li_4P_2O_7$ and$LiFePO_4$ materials. The purpose of this study was to know the structure of the solid electrolyte interphase (SEI) in lithium ion cells composed of $LiFePO_4$ as cathode material. $Li_4P_2O_7$ and $LiFePO_4$ were prepared by a solid-state reaction. The $^7Li$ MAS NMR experiments were carried out at variable temperatures in order to observe the local structure changes at the temperatures in $Li_4P_2O_7$ system. The $^7Li$ MAS NMR spectra of in $Li_4P_2O_7$ indicate that the lithium local environments in $Li_4P_2O_7$ were not changed in the temperature range between $27^{\circ}C$ and $97^{\circ}C$ Through this work, we confirmed that the small amount of $Li_4P_2O_7$ less than 5.0 wt% in $LiFePO_4$ could be clearly measured by the $^7Li$ MAS NMR spectroscopy at high spinning rate over than 11 kHz.

Structural and Electrochemical Characterization of LiFePO4 Synthesized by Hydrothermal Method

전연수,김은미,진보,전대교,한젠지,구할본 한국전기전자재료학회 2007 Transactions on Electrical and Electronic Material Vol.8 No.1

Phospho-olivine LiFePO4 cathode materials were prepared by hydrothermal reaction. Carbon black was added to enhance the electrical conductivity of LiFePO4. The structural and morphological performance of LiFePO4 and LiFePO4-C powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). LiFePO4/Li and LiFePO4-C/Li cells were characterized electrochemically by cyclic voltammogram (CV), charge/discharge experiments and ac impedance spectroscopy. The results showed that the discharge capacity of LiFePO4/Li cell was 147 mAh/g at the first cycle and 118 mAh/g after 30 cycles, respectively. The discharge capacity of LiFePO4-C/Li cell with 5 wt% carbon black was the largest among LiFePO4-C/Li cells, 133 mAh/g at the first cycle and 128 mAh/g after 30 cycles, respectively. It was demonstrated that cycling performance of LiFePO4-C/Li cell with 5 wt% carbon black was better than that of LiFePO4/Li cell.

Structural and Electrochemical Characterization of LiFePO₄ Synthesized by Hydrothermal Method

Jeon, Yeon-Su,Jin, En-Mei,Jin, Bo,Jun, Dae-Kyoo,Han, Zhen-Ji,Gu, Hal-Bon The Korean Institute of Electrical and Electronic 2007 Transactions on Electrical and Electronic Material Vol.8 No.1

Phospho-olivine $LiFePO_4$ cathode materials were prepared by hydrothermal reaction. Carbon black was added to enhance the electrical conductivity of $LiFePO_4$. The structural and morphological performance of $LiFePO_4$ and $LiFePO_4$-C powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). $LiFePO_4$/Li and $LiFePO_4$-C/Li cells were characterized electrochemically by cyclic voltammogram (CV), charge/discharge experiments and ac impedance spectroscopy. The results showed that the discharge capacity of $LiFePO_4$/Li cell was 147 mAh/g at the first cycle and 118 mAh/g after 30 cycles, respectively. The discharge capacity of $LiFePO_4$-C/Li cell with 5 wt% carbon black was the largest among $LiFePO_4$-C/Li cells, 133 mAh/g at the first cycle and 128 mAh/g after 30 cycles, respectively. It was demonstrated that cycling performance of $LiFePO_4$-C/Li cell with 5 wt% carbon black was better than that of $LiFePO_4$/Li cell.

Synthesis LiFePO4- poly(sodium 4-styrenesulfonate) composite cathode material for rechargeable lithium battery by hydrothermal method

Hiep, Nguyen Van,Wang, Wan Lin,Jin, En Mei,Gu, Hal-Bon 한국신재생에너지학회 2011 한국신재생에너지학회 학술대회논문집 Vol.2011 No.11

Poly (sodium 4-styrenesulfonate) (PSS) is ionomer based on polystyrene that is electrical conductivity and isoviscosity. LiFePO4 has been a promising electrode material however its poor conductivity limits practical application. To enhance the electronic conductivity of LiFePO4, in this study we prepared LiFePO4- PSS composite by the hydrothermal method. LiFePO4 was heated at 170?C for 12h and then different wt% PSS (0%, 2.91%, 4.75%, 7.36%, 10%) are added to LiFePO4 and milled at 300rpm for 10h. And then the obtained powders were subsequently heated at 500?C for 1h under argon flow. The cathode electrode were made from mixtures of LiFePO4-PSS: SP-270- PVDF in a weighting ratio 75%: 25%:5%. The electrochemical properties of LiFePO4- PSS/Li batteries were analyzed by cyclic voltammetry and charge/discharge tests. LiFePO4-C/Li battery with 4.75 wt% PSS displays discharge capacity of 128 mAh g-1 at room temperature that is considerably higher than pure LiFePO4/Li battery ( 113.48 mAhg-1).

2P-750 Electospun LiFePO₄/carbon complex for high rate performance lithium ion battery

정민정,한정인,이영석 한국공업화학회 2017 한국공업화학회 연구논문 초록집 Vol.2017 No.1

LiFePO₄/carbon complexes were prepared by electrospinning to improve rate performance at high C-rate and their electrochemical properties were investigated to be used as a cathode active material for lithium ion battery. The LiFePO₄/carbon complexes prepared have a continuous structure with carbon-coated LiFePO₄ and the LiFePO₄ in LiFePO₄/carbon complex has improved thermal stability from carbon coating. The capacity ratio of coin cell manufactured from raw LiFePO₄ is 40%, whereas the capacity ratio of coin cell manufactured from LiFePO₄/carbon complex is 61% (10 C/0.1 C).

The Root Cause of the Rate Performance Improvement After Metal Doping: A Case Study of LiFePO₄

Park, Chang-Kyoo,Park, Sung-Bin,Park, Ji-Hun,Shin, Ho-Chul,Cho, Won-Il,Jang, Ho Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.3

This study investigates a root cause of the improved rate performance of $LiFePO_4$ after metal doping to Fesites. This is because the metal doped $LiFePO_4$/C maintains its initial capacity at higher C-rates than undoped one. Using $LiFePO_4$/C and doped $LiFe_{0.97}M_{0.03}PO_4$/C (M=$Al^{3+}$, $Cr^{3+}$, $Zr^{4+}$), which are synthesized by a mechanochemical process followed by one-step heat treatment, the Li content before and after chemical delithiation in the $LiFePO_4$/C and the binding energy are compared using atomic absorption spectroscopy (AAS) and X-ray photoelectron spectroscopy (XPS). The results from AAS and XPS indicate that the low Li content of the metal doped $LiFePO_4$/C after chemical delithiation is attributed to the low binding energy induced by weak Li-O interactions. The improved capacity retention of the doped $LiFePO_4$/C at high discharge rates is, therefore, achieved by relatively low binding energy between Li and O ions, which leads to fast Li diffusivity.

Surface Treatment of LiFePo4 Cathode Material for Lithium Secondary Battery

손종태 한국전기화학회 2010 한국전기화학회지 Vol.13 No.4

In this study, nano-crystallized Al2O3 was coated on the surface of LiFePO4 powders via a novel dry coating method. The influence of coated LiFePO4 upon electrochemical behavior was discussed. Surface morphology characterization was achieved by transmission electron microscopy (TEM), clearly showing nano-crystallized Al2O3 on LiFePO4 surfaces. Furthermore,it revealed that the Al2O3-coated LiFePO4 cathode exhibited a distinct surface morphology. It was also found that the Al2O3 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 Al2O3 can prevent structural change of LiFePO4 or reaction with the electrolyte on cycling. In addition, the Al2O3coated LiFePO4 compound showed highly improved area-specific impedance (ASI), an important measure of battery performance. From the correlation between these characteristics of bare and coated LiFePO4, the role of Al2O3 coating played on the electrochemical performance of LiFePO4was probed.

Electrochemical Characteristics of Carbon-coated LiFePO4 as a Cathode Material for Lithium Ion Secondary Batteries

조원일,신호철,이병조,조병원,장호 한국전기화학회 2005 한국전기화학회지 Vol.8 No.4

The electrochemical properties of LiFePO4 as a cathode for Li-ion batteries were improved by incorporating conductive carbon into the LiFePO4. X-ray diffraction analysis and SEM observations revealed that the carbon-coated LiFePO4 consisted of fine single crystalline particles, which were smaller than the bare LiFePO4. The electrochemical performance of the carbon-coated LiFePO4 was tested under various conditions. The carbon-coated LiFePO4 showed much better performance in terms of the discharge capacity and cycling stability than the bare LiFePO4. The improved electrochemical performances were found to be attributed to the reduced particle size and enhanced electrical conductivity of the LiFePO4 by the carbon.

리튬폴리머전지용 정극활물질 LiFePO₄의 전기화학적 특성

공명철,김현수,구할본,Kong Ming-Zhe,Kim Hyun-Soo,Gu Hal-Bon 한국전기전자재료학회 2006 전기전자재료학회논문지 Vol.19 No.6

$LiFePO_4$ has been received attention as a potential cathode material for the lithium secondary batteries. In our study, $LiFePO_4$ cathode active materials were synthesized by a solid-state reaction. It was modified by coating $TiO_2$ and carbon in order to enhance cyclic performance and electronic conductivity. $TiO_2$ and carbon coatings on $LiFePO_4$ materials enhanced the electronic conductivity and its charge/discharge capacity. For lithium polymer battery applications, $LiFePO_4$/solid polymer electrolyte (SPE)/Li and $LiFePO_{4}-TiO_{2}/SPE/Li$ cells were characterized by a cyclic voltammetry and charge/discharge cycling. The electrode with $LiFePO_{4}-carbon-TiO_{2}$ in PVDF-PC-EC-$LiClO_{4}$ electrolyte showed promising capacity of above 100 mAh/g at 1C rate.