共查询到20条相似文献,搜索用时 15 毫秒
1.
Hee-Cheol Kang Dae-Kyoo Jun Bo Jin En Mei Jin Kyung-Hee Park Hal-Bon Gu Ki-Won Kim 《Journal of power sources》2008
Olivine-type LiFePO4 cathode materials were synthesized by a solid-state reaction method and ball-milling. The ball-milling time, heating time and heating temperature are optimized. A heating temperature higher than 700 °C resulted in the appearance of impurity phase Fe2P and growth of large particle, which was shown by high resolution X-ray diffraction and field emission scanning electron microscopy. The impurity phase Fe2P exhibited a considerable capacity loss at the 1st cycle and a gradual increase in discharge capacity upon cycling. Moreover, it exhibited an excellent high-rate capacity of 104 mAh g−1 at 3 C in spite of the large particle size. The optimum synthesis conditions for LiFePO4 were ball-milling for 24 h and heat-treatment at 600 °C for 3 h. LiFePO4/Li cells showed an enhanced cycling performance and a high discharge capacity of 160 mAh g−1 at 0.1 C. 相似文献
2.
Jae-Kwang Kim Gouri Cheruvally Jae-Won Choi Jong-Uk Kim Jou-Hyeon Ahn Gyu-Bong Cho Ki-Won Kim Hyo-Jun Ahn 《Journal of power sources》2007
Pure, nano-sized LiFePO4 and carbon-coated LiFePO4 (LiFePO4/C) positive electrode (cathode) materials are synthesized by a mechanical activation process that consists of high-energy ball milling and firing steps. The influence of the processing parameters such as firing temperature, firing time and ball-milling time on the structure, particle size, morphology and electrochemical performance of the active material is investigated. An increase in firing temperature causes a pronounced growth in particle size, especially above 600 °C. A firing time longer than 10 h at 600 °C results in particle agglomeration; whereas, a ball milling time longer than 15 h does not further reduce the particle size. The electrochemical properties also vary considerably depending on these parameters and the highest initial discharge capacity is obtained with a LiFePO4/C sample prepared by ball milling for 15 h and firing for 10 h at 600 °C. Comparison of the cyclic voltammograms of LiFePO4 and LiFePO4/C shows enhanced reaction kinetics and reversibility for the carbon-coated sample. Good cycle performance is exhibited by LiFePO4/C in lithium batteries cycled at room temperature. At the high current density of 2C, an initial discharge capacity of 125 mAh g−1 (73.5% of theoretical capacity) is obtained with a low capacity fading of 0.18% per cycle over 55 cycles. 相似文献
3.
Jiangfeng Ni Masanori Morishita Masaharu Watada Tetsuo Sakai 《Journal of power sources》2010,195(9):2877-2882
Well-crystallized LiFePO4 nanoparticles have been directly synthesized in a short time via hydrothermal process in the presence of organic acid, e.g. citric acid or ascorbic acid. These acid-mediated LiFePO4 products exhibit a phase-pure and nanocrystal nature with size about 50-100 nm. Two critical roles that the organic acid mediator plays in hydrothermal process are recognized and a rational mechanism is explored. After a post carbon-coating treatment at 600 °C for 1 h, these mediated LiFePO4 materials show a high electrochemical activity in terms of reversible capacity, cycling stability and rate capability. Particularly, LiFePO4 mediated by ascorbic acid can deliver a capacity of 162 mAh g−1 at 0.1 C, 154 mAh g−1 at 1 C, and 122 mAh g−1 at 5 C. The crystalline structure, particle morphology, and surface microstructure were characterized by high-energy synchrotron X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and Raman spectroscopy, respectively. And the electrochemical properties were thoroughly investigated by galvanostatic test and electrochemical impedance spectroscopy (EIS). 相似文献
4.
Phospho-olivine LiFePO4 cathode materials were prepared by hydrothermal reaction at 150 °C. Carbon black was added to enhance the electrical conductivity of LiFePO4. LiFePO4-C powders (0, 3, 5 and 10 wt.%) were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). LiFePO4-C/solid polymer electrolyte (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+, cyclic voltammetry (CV) and ac impedance spectroscopy. The results showed that initial discharge capacity of LiFePO4 was 104 mAh g−1. The discharge capacity of LiFePO4-C/SPE/Li cell with 5 wt.% carbon black was 128 mAh g−1 at the first cycle and 127 mAh g−1 after 30 cycles, respectively. It was demonstrated that cycling performance of LiFePO4-C/SPE/Li cells was better than that of LiFePO4/SPE/Li cells. 相似文献
5.
The Nam Long DoanIzumi Taniguchi 《Journal of power sources》2011,196(3):1399-1408
LiMnPO4/C nanocomposites could be prepared by a combination of spray pyrolysis and wet ball-milling followed by heat treatment in the range of spray pyrolysis temperature from 200 to 500 °C. The ordered LiMnPO4 olivine structure without any impurity phase could be identified by X-ray diffraction analysis for all samples. It could be also confirmed from scanning electron microscopy and transmission electron microscopy observations that the final samples were the LiMnPO4/C nanocomposites with approximately 100 nm in primary particles size. The LiMnPO4/C nanocomposite samples were used as cathode active materials for lithium batteries, and the electrochemical tests were carried out for the cell Li|1 M LiPF6 in EC:DMC = 1:1|LiMnPO4/C at various charge/discharge rates in three charge modes. As a result, the final sample which was synthesized at 300 °C by spray pyrolysis showed the best electrochemical performance due to the largest specific surface area, the smallest primary particle size and a well distribution of carbon. At galvanostatic charge/discharge rates of 0.05 C, the cell delivered first discharge capacities of 123 and 165 mAh g−1 in correspondence to charge cutoff voltages of 4.4 and 5.0 V, respectively. Furthermore, in a constant current-constant voltage charge mode at 4.4 V, the cells also exhibited initial discharge capacities of 147 mAh g−1 at 0.05 C, 145 mAh g−1 at 0.1 C, 123 mAh g−1 at 1 C and 65 mAh g−1 at 10 C. Moreover, the cells showed fair good cycleability over 100 cycles. 相似文献
6.
Min-Sang Song Yong-Mook Kang Jin-Ho Kim Hyun-Seok Kim Dong-Yung Kim Hyuk-Sang Kwon Jai-Young Lee 《Journal of power sources》2007
A very simple and rapid method for synthesizing LiFePO4-C composite has been developed by vibrant type ball-milling for 30 min and microwave heating for 2–4 min. X-ray diffraction and Mössbauer spectroscopy verify that well-crystallized LiFePO4 without Fe3+ impurities is obtained. From laser particle size analysis and transmission electron microscopy, it is confirmed that a LiFePO4-C composite with fine and uniform particle size (mean particle size ≤0.640 μm, D75 in volume distribution ≤0.592 μm) and with extremely uniform carbon distribution is prepared by vibrant type ball-milling and microwave heating. The LiFePO4-C delivers a high initial discharge capacity of 161 mAh g−1 at C/10 and shows very stable cycling behaviour. 相似文献
7.
Qiang Wang Weixin Zhang Zeheng Yang Shaoying Weng Zhuojie Jin 《Journal of power sources》2011,196(23):10176-10182
Hierarchical LiFePO4 microflowers have been successfully synthesized via a solvothermal reaction in ethanol solvent with the self-prepared ammonium iron phosphate rectangular nanoplates as a precursor, which is obtained by a simple water evaporation method beforehand. The hierarchical LiFePO4 microflowers are self-assemblies of a number of stacked rectangular nanoplates with length of 6-8 μm, width of 1-2 μm and thickness of around 50 nm. When ethanol is replaced with the water-ethanol mixed solvent in the solvothermal reaction, LiFePO4 micro-octahedrons instead of hierarchical microflowers can be prepared. Then both of them are respectively modified with carbon coating through a post-heat treatment and their morphologies are retained. As a cathode material for rechargeable lithium ion batteries, the carbon-coated hierarchical LiFePO4 microflowers deliver high initial discharge capacity (162 mAh g−1 at 0.1 C), excellent high-rate discharge capability (101 mAh g−1 at 10 C), and cycling stability, which exhibits better electrochemical performances than carbon-coated LiFePO4 micro-octahedrons. These enhanced electrochemical properties can be attributed to the hierarchical micro/nanostructures, which can take advantage of structure stability of micromaterials for long-term cycling. Furthermore the rectangular nanoplates as the building blocks can improve the electrochemical reaction kinetics and finally promote the rate performance. 相似文献
8.
Physical and electrochemical properties of LiFePO4 nanoparticles synthesized by a combination of spray pyrolysis with wet ball-milling 总被引:1,自引:0,他引:1
A novel preparation technique was developed to synthesize LiFePO4 nanoparticles through a combination of spray pyrolysis (SP) with wet ball-milling (WBM). Using this technique, the preparation of LiFePO4 nanoparticles was investigated for a wide range of process parameters such as ball-milling time and sintering temperature. The effect of process parameters on the physical and electrochemical properties of LiFePO4 was then discussed through analysis using by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), the Brunauer–Emmet–Teller (BET) method, Raman spectroscopy and using an electrochemical cell of Li|1 M LiClO4 in EC:DEC = 1:1|LiFePO4. LiFePO4 nanoparticles with a geometric mean diameter of 58 nm were prepared at a rotating speed of 800 rpm and a ball-milling time of 12 h in an Ar atmosphere followed by heat treatment at 500 °C for 4 h in a N2 + 3% H2 atmosphere. The sample delivered first discharge capacities of 164 and 100 mAh g−1 at charge–discharge rates of 0.1 and 10 C in the test cells, respectively. The electrochemical properties of LiFePO4 nanoparticles were strongly affected by the formation of Fe2P, Fe3P and α-Fe2O3 at higher charge–discharge rates. 相似文献
9.
LiFePO4/carbon composite electrode was prepared and applied to the dry polymer electrolyte. Enhanced low-temperature performance of LiFePO4 was achieved by modifying the interface between LiFePO4 and polymer electrolyte. The molecular weight of the polymer and the salt concentration as the Li/O ratio were optimized at 3 × 105 and 1/10, respectively. Impedance analysis revealed that a small resistive component occurred in the frequency range of the charge transfer process. The reversible capacity of the laminate cell was 140 mAh g−1 (C/20) and 110 mAh g−1 (C/2) at 40 °C, which is comparable to the performance in the liquid electrolyte system. 相似文献
10.
W.L. LiuJ.P. Tu Y.Q. QiaoJ.P. Zhou S.J. ShiX.L. Wang C.D. Gu 《Journal of power sources》2011,196(18):7728-7735
A nanosized LiFePO4/C composite with a complete and thin carbon-shell is synthesized via a ball-milling route followed by solid-state reaction using poly(vinvl alcohol) as carbon source. The LiFePO4/C nanocomposite delivers discharge capacities of 159, 141, 124 and 112 mAh g−1 at 1 C, 5 C, 15 C and 20 C, respectively. Even at a charge-discharge rate of 30 C, there is still a high discharge capacity of 107 mAh g−1 and almost no capacity fading after 1000 cycles. Based on the analysis of cyclic voltammograms, the apparent diffusion coefficients of Li ions in the composite are in the region of 2.42 × 10−11 cm2 s−1 and 2.80 × 10−11 cm2 s−1. Electrochemical impedance spectroscopy and galvanostatic intermittent titration technique are also used to calculate the diffusion coefficients of Li ions in the LiFePO4/C electrode, they are in the range of 10−11-10−14 cm2 s−1. In addition, at −20 °C, it can still deliver a discharge capacity of 122 mAh g−1, 90 mAh g−1 and 80 mAh g−1 at the charge-discharge rates of 0.1 C, 0.5 C and 1 C, respectively. 相似文献
11.
Two types of carbon source and precursor mixing pellets were employed simultaneously to prepare the LiFePO4/C composite materials: Type I using the LiFePO4 precursor with 20 wt.% polystyrene (PS) as a primary carbon source, and Type II using the LiFePO4 precursor with 50 wt.% malonic acid as a secondary carbon vapor source. During final sintering, a Type I pellet was placed down-stream and Type II precursor pellet(s) was(were) placed upstream next to a Type I precursor pellet in a quartz-tube furnace. The carbon-coated product of the sintered Type I precursor pellet was obtained by using both PS and malonic acid as carbon sources. When two Type II pellets were used as a carbon vapor source (defined as Product-2), a more uniform film between 4 and 8 nm was formed, as shown in the TEM images. In the absence of a secondary carbon source (defined as Product-0), the discharge capacity of Product-0 was 137 mAh g−1 with 100 cycles at a 0.2C-rate, but Product-2 demonstrated a high capacity of 151 mAh g−1 with 400 cycles. Our results indicate that electrochemical properties of LiFePO4 are correlated to the amount of carbon and its coating thickness and uniformity. 相似文献
12.
C.S. Sun 《Journal of power sources》2010,195(11):3680-8838
Cl-doped LiFePO4/C cathode materials were synthesized through a carbothermal reduction route, and the microstructure and electrochemical performances were systematically studied. Cl-doped LiFePO4/C cathode materials presented a high discharge capacity of ∼90 mAh g−1 at the rate of 20 C (3400 mA g−1) at room temperature. Electrochemical impedance spectroscopy and cyclic voltamperometry indicated the optimized electrochemical reaction and Li+ diffusion in the bulk of LiFePO4 due to Cl-doping. The improved Li+ diffusion capability is attributed to the microstructure modification of LiFePO4 via Cl-doping. 相似文献
13.
Carbon Nano Fibers (CNFs) coated with LiFePO4 particles have been prepared by a non-aqueous sol–gel technique. The functionalization of the CNFs by HNO3 acid treatment has been confirmed by Raman and XPS analyses. The samples pure LiFePO4 and LiFePO4–CNF have been characterized by XRD, SEM, RAMAN, XPS and electrochemical analysis. The LiFePO4–CNF sample shows better electrochemical performance compared to as-prepared LiFePO4. LiFePO4–CNF (10 wt.%) delivers a higher specific capacity (∼140 mAh g−1) than LiFePO4 with carbon black (25 wt.%) added after synthesis (∼120 mAh g−1) at 0.1C. 相似文献
14.
V-doped LiFePO4/C cathode materials were prepared through a carbothermal reduction route. The microstructure was characterized by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The electrochemical Li+ intercalation performances of V-doped LiFePO4/C were compared with those of undoped one through galvanostatic intermittent titration technique, cyclic voltamperometry, and electrochemical impedance spectrum. V-doped LiFePO4/C showed a high discharge capacity of ∼70 mAh g−1 at the rate of 20 C (3400 mA g−1) at room temperature. The significantly improved high-rate charge/discharge capacity is attributed to the increase of Li+ ion “effective” diffusion capability. 相似文献
15.
An order olivine structure LiFePO4 was synthesized with a simple rheological phase reaction (RPR) of LiOH·H2O and FePO4·4H2O in the presence of PEG as a reductive agent and carbon source. A required amount of water was added to the starting materials to form the rheological precursor and decomposed at 700 °C to form the crystalline phase LiFePO4 directly, without ball-milling, preparation of intermediates, pre-sintering and post-deposition treatment. Fine particles with an average particle size about 216 nm are examined by scanning electron microscopy (SEM) and optical particle size analyzer. An initial discharge capacity of 157 mAh g−1 was achieved for the as-prepared LiFePO4 material with a rate of 0.1C (17 mA g−1), what's more, this material shows excellent specific capacity, charge–discharge efficiency and cycle efficiency at high current rates, almost no capacity loss can be observed up to 40 cycles with the rate of 1, 2 and 3C at room temperature. The simple, cheap process as well as the excellent high-rate performance makes this RPR method feasible commercially. 相似文献
16.
Tomoyuki Shiratsuchi Shigeto Okada Jun-ichi Yamaki Shohei Yamashita Tetsuaki Nishida 《Journal of power sources》2007
Chemical lithiation with LiI in acetonitrile was performed for amorphous FePO4 synthesized from an equimolar aqueous suspension of iron powder and an aqueous solution of P2O5. An orthorhombic LiFePO4 olivine structure was obtained by annealing a chemically lithiated sample at 550 °C for 5 h in Ar atmosphere. The average particle size remained at approximately 250 nm even after annealing. The lithium content in the sample was quantitatively confirmed by Li atomic absorption analysis and 57Fe Mössbauer spectroscopy. While an amorphous FePO4/carbon composite cathode has a monotonously decreasing charge–discharge profile with a reversible capacity of more than 140 mAh g−1, the crystallized LiFePO4/carbon composite shows a 3.4 V plateau corresponding to a two-phase reaction. This means that the lithium in the chemically lithiated sample is electrochemically active. Both amorphous FePO4 and the chemically lithiated and annealed crystalline LiFePO4 cathode materials showed good cyclability (more than 140 mAh g−1 at the 40th cycle) and good discharge rate capability (more than 100 mAh g−1 at 5.0 mA cm−2). In addition, the fast-charge performance was found to be comparable to that with LiCoO2. 相似文献
17.
A carbon-coated nanocrystalline LiFePO4 cathode material was synthesized by pyrolysis of polyacrylate precursor containing Li+, Fe3+ and PO4−. The powder X-ray diffraction (XRD) and high-resolution TEM micrographs revealed that the LiFePO4/C composite as prepared has a core-shell structure with pure olivine LiFePO4 crystallites as cores and intimate carbon coating as a shell layer. Between the composite particulates, there exists a carbon matrix binding the nanocrystallites together into micrometer particles. The electrochemical measurements demonstrated that the LiFePO4/C composite with an appropriate carbon content can deliver a very high discharge capacity of 157 mAh g−1 (>92% of the theoretical capacity of LiFePO4) with 95% of its initial capacity after 30 cycles. Since this preparation method uses less costly materials and operates in mild synthetic conditions, it may provide a feasible way for industrial production of the LiFePO4/C cathode materials for the lithium-ion batteries. 相似文献
18.
LiFePO4 cathode materials with distinct particle sizes were prepared by a planetary ball-milling method. The effects of particle size on the morphology, thermal stability and electrochemical performance of LiFePO4 cathode materials were investigated. The ball-milling method decreased particle size, thereby reducing the length of diffusion and improving the reversibility of the lithium ion intercalation/deintercalation. It is worth noting that the small particle sample prepared using malonic acid as a carbon source achieved a high capacity of 161 mAh g−1 at a 0.1 C rate and had a very flat capacity curve during the early 50 cycles. However, the big particle samples (∼400 nm) decayed more dramatically in capacity than the small particle size samples (∼200 nm) at high current densities. The improvement in electrode performance was mainly due to the fine particles, the small size distribution, and the increase in electronic conductivity as a result of carbon coating. The structure and morphology of the ground LiFePO4 samples were characterized with XRD, FE-SEM, TEM, EDS, and DSC techniques. 相似文献
19.
Porous nanostructured LiFePO4 powder with a narrow particle size distribution (100–300 nm) for high rate lithium-ion battery cathode application was obtained using an ethanol based sol–gel route employing lauric acid as a surfactant. The synthesized LiFePO4 powders comprised of agglomerates of crystallites <65 nm in diameter exhibiting a specific surface area ranging from 8 m2 g−1 to 36 m2 g−1 depending on the absence or presence of the surfactant. The LiFePO4 obtained using lauric acid resulted in a specific capacity of 123 mAh g−1 and 157 mAh g−1 at discharge rates of 10C and 1C with less than 0.08% fade per cycle, respectively. Structural and microstructural characterization were performed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) with energy dispersive X-ray (EDX) analysis while electronic conductivity and specific surface area were determined using four-point probe and N2 adsorption techniques. 相似文献
20.
Y. Kobayashi S. Seki Y. Mita Y. Ohno H. Miyashiro P. Charest A. Guerfi K. Zaghib 《Journal of power sources》2008
The combination of graphite or silicon monoxide (SiO)/graphite = 1/1 mixture with a solvent-free solid polymer electrolyte (SPE) was fabricated using a new preparation process, involving precoating the electrode with vapor-grown carbon fiber (VGCF) and binders (polyvinyl difluoride: PVdF or polyimide: PI), followed by the overcoating of the SPE. The reversible capacity of [graphite | SPE | Li] and [SiO/graphite | SPE | Li] cells were >360 and >1000 mAh g−1 with 78% and 77% for the 1st Coulombic efficiency, respectively. The reversible capacities were 75% at the 250th cycle for [graphite | SPE | Li] and 72% at the 100th cycle for [SiO/graphite | SPE | Li]. The electrode used was compatible with that of the conventional liquid electrolyte system, and the SPE film could be formed on the electrode by the continuous overcoating process, which will lead to a low-cost electrodes and low-cost battery production. The solid-state lithium-ion polymer battery (SSLiPB) developed in this study, which consisted of [LiFePO4 | SPE | graphite], showed the reversible capacity of 128 mAh g−1 (based on the LiFePO4 capacity) with favorable cycle performance. 相似文献