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1.
LiFePO4/C composite cathode materials were synthesized by carbothermal reduction method using inexpensive FePO4 as raw materials and glucose as conductive additive and reducing agent. The precursor of LiFePO4/C was characterized by differential thermal analysis and thermogravimetry. The microstructure and morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and particle size analysis. Cyclic voltammetry (CV) and charge/discharge cycling performance were used to characterize their electrochemical properties. The results showed that the LiFePO4/C composite synthesized at 650 °C for 9 h exhibited the most homogeneous particle size distribution. Residual carbon during processing was coated on LiFePO4, resulting in the enhancement of the material's electronic properties. Electrochemical measurements showed that the discharge capacity first increased and then decreased with the increase of synthesis temperature. The optimal sample synthesized at 650 °C for 9 h exhibited a highest initial discharge capacity of 151.2 mA h g−1 at 0.2 C rate and 144.1 mA h g−1 at 1 C rate with satisfactory capacity retention rate. 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.
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
4.
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
5.
LiFePO4/C composite was synthesized at 600 °C in an Ar atmosphere by a soluble starch sol assisted rheological phase method using home-made amorphous nano-FePO4 as the iron source. XRD, SEM and TEM observations show that the LiFePO4/C composite has good crystallinity, ultrafine sphere-like particles of 100-200 nm size and in situ carbon. The synthesized LiFePO4 could inherit the morphology of FePO4 precursor. The electrochemical performance of the LiFePO4 by galvanostatic cycling studies demonstrates excellent high-rate cycle stability. The Li/LiFePO4 cell displays a high initial discharge capacity of more than 157 mAh g−1 at 0.2C and a little discharge capacity decreases from the first to the 80th cycle (>98.3%). Remarkably, even at a high current density of 30C, the cell still presents good cycle retention. 相似文献
6.
Jie Li Zhi’an Zhang Fanqun Li Xin Hao Xujie Chen Yexiang Liu 《Journal of power sources》2010,195(16):5344-5350
The electrolytes based on lithium oxalyldifluoroborate (LiODFB) and carbonates have been systematically investigated for LiFePO4/artificial graphite (AG) cells, by ionic conductivity test and various electrochemical tests, such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge-discharge test. The conductivity of nine electrolytes as a function of solvent composition and LiODFB salt concentration has been studied. The coulombic efficiency of LiFePO4/Li and AG/Li half cells with these electrolytes have also been compared. The results show that 1 M LiODFB EC/PC/DMC (1:1:3, v/v) electrolyte has a relatively higher conductivity (8.25 mS cm−1) at 25 °C, with high coulombic efficiency, good kinetics characteristics and low interface resistance. With 1 M LiODFB EC/PC/DMC (1:1:3, v/v) electrolyte, LiFePO4/AG cells exhibit excellent capacity retention ∼92% and ∼88% after 100 cycles at 25 °C and at elevated temperatures up to 65 °C, respectively; The LiFePO4/AG cells also have good rate capability, the discharge capacity is 324.8 mAh at 4 C, which is about 89% of the discharge capacity at 0.5 C. However, at −10 °C, the capacity is relatively lower. Compared with 1 M LiPF6 EC/PC/DMC (1:1:3, v/v), LiFePO4/AG cells with 1 M LiODFB EC/PC/DMC (1:1:3, v/v) exhibited better capacity utilization at both room temperature and 65 °C. The capacity retention of the cells with LiODFB-based electrolyte was much higher than that of LiPF6-based electrolyte at 65 °C, while the capacity retention and the rate capacity of the cells is closed to that of LiPF6-based electrolyte at 25 °C. In summary, 1 M LiODFB EC/PC/DMC (1:1:3, v/v) is a promising electrolyte for LiFePO4/AG cells. 相似文献
7.
M.L. TrudeauD. Laul R. VeilletteA.M. Serventi A. MaugerC.M. Julien K. Zaghib 《Journal of power sources》2011,196(18):7383-7394
In situ high-resolution transmission electron microscopy (HRTEM) studies of the structural transformations that occur during the synthesis of carbon-coated LiFePO4 (C-LiFePO4) and heat treatment to elevated temperatures were conducted in two different electron microscopes. Both microscopes have sample holders that are capable of heating up to 1500 °C, with one working under high vacuum and the other capable of operating with the sample surrounded by a low gaseous environment. The C-LiFePO4 samples were prepared using three different compositions of precursor materials with Fe(0), Fe(II) or Fe(III), a Li-containing salt and a polyethylene-block-poly(ethylene glycol)-50% ethylene oxide or lactose. The in situ TEM studies suggest that low-cost Fe(0) and a low-cost carbon-containing compound such as lactose are very attractive precursors for mass production of C-LiFePO4, and that 700 °C is the optimum synthesis temperature. At temperatures higher than 800 °C, LiFePO4 has a tendency to decompose. The same in situ measurements have been made on particles without carbon coat. The results show that the homogeneous deposit of the carbon deposit at 700 °C is the result of the annealing that cures the disorder of the surface layer of bare LiFePO4. Electrochemical tests supported the conclusion that the C-LiFePO4 derived from Fe(0) is the most attractive for mass production. 相似文献
8.
Cycling degradation of an automotive LiFePO4 lithium-ion battery 总被引:2,自引:0,他引:2
Degradation of a high capacity prismatic LiFePO4 cell with deep cycling at elevated temperature of 50 °C is studied by electrochemical impedance spectroscopy as well as capacity and power fading characterization at different test temperatures (45, 25, 0 and −10 °C). Capacity fade after 600 cycles is 14.3% at 45 °C and 25.8% at −10 °C. There is little power fade at 45 °C after 600 cycles, whereas the power fade after 600 cycles is 61.6% and 77.2%, respectively, at 0 and −10 °C. The capacity and power fade evidently becomes more severe at lower temperature. In particular, the power fade at low temperatures (e.g., 0 and −10 °C) rather than capacity loss is a major limitation of the LiFePO4 cell. The primary mechanism for capacity fade is loss of cyclable lithium in the cell resulting from lithium-consuming solid electrolyte interphase (SEI) layer growth and side reactions. The increased interfacial resistance (Rw) due to the catalytic growth of SEI layer on the graphite anode and increased electrolyte resistance are the main sources for power fade. 相似文献
9.
LiFePO4 as a cathode material for rechargeable lithium batteries was prepared by hydrothermal process at 170 °C under inert atmosphere. The starting materials were LiOH, FeSO4, and (NH4)2HPO4. The particle size of the obtained LiFePO4 was 0.5 μm. The electrochemical properties of LiFePO4 were characterized in a mixed solvent of ethylene carbonate and diethyl carbonate (1:1 in volume) containing 1.0 mol dm−3 LiClO4. The hydrothermally synthesized LiFePO4 exhibited a discharge capacity of 130 mA h g−1, which was smaller than theoretical capacity (170 mA h g−1). The annealing of LiFePO4 at 400 °C in argon atmosphere was effective in increasing the discharge capacity. The discharge capacity of the annealed LiFePO4 was 150 mA h g−1. 相似文献
10.
Effects of TiO2 coating on high-temperature cycle performance of LiFePO4-based lithium-ion batteries
Hao-Hsun Chang Chun-Chih Chang Ching-Yi Su Hung-Chun Wu Mo-Hua Yang Nae-Lih Wu 《Journal of power sources》2008
LiFePO4 particles were coated with TiO2 (molar ratio = 3%) via a sol–gel process, and the effects of the coating on cycle performance of LiFePO4 cathode at 55 °C against either a Li or a C (mesocarbon microbead) anode were investigated. It was found that, while the coating reduces capacity fading of the LiFePO4/Li cell, it imposes a deteriorating effect on the LiFePO4/C cell. Analyses on cell impedance and electrode surface morphology and composition showed that the oxide coating reduced Fe dissolution from the LiFePO4 cathode and hence alleviated the impedance increase associated with the erosion process. This leads to reduced capacity fading as observed for the LiFePO4/Li cell. However, the oxide coating itself was eroded upon cycling, and the dissolved Ti ions were subsequently reduced at the anode surface. Ti deposit on the C anode was found to be more active than Fe in catalyzing the formation of the solid-electrolyte interphase (SEI) layer, causing accelerated capacity decay for the LiFePO4/C cell. The results point out the importance of evaluating the effect of cathode coating material on the anode side, which has generally been overlooked in the past studies. 相似文献
11.
Pure LiFePO4 was synthesized by heating an amorphous LiFePO4. The amorphous LiFePO4 obtained through lithiation of FePO4·xH2O by using oxalic acid as a novel reducing agent at room temperature. FePO4·xH2O was prepared through co-precipitation by employing FeSO4·7H2O and H3PO4 as raw materials. X-ray diffraction (XRD), scanning electron microscopy (SEM) observations showed that LiFePO4 composites with fine particle sizes between 100 nm and 200 nm, and with homogenous sizes distribution. The electrochemical performance of LiFePO4 powder synthesized at 500 °C were evaluated using coin cells by galvanostatic charge/discharge. The synthesized LiFePO4 composites showed a high electrochemical capacity of 166 mAh g−1 at the 0.1C rate, and possessed a favorable capacity cycling maintenance at the 0.1C, 0.2C, 0.5C and 1C rate. 相似文献
12.
Muxina Konarova 《Journal of power sources》2010,195(11):3661-3667
A novel preparation technique was developed for synthesizing carbon-coated LiFePO4 nanoparticles through a combination of spray pyrolysis (SP) with wet ball milling (WBM) followed by heat treatment. Using this technique, the preparation of carbon-coated LiFePO4 nanoparticles was investigated for a wide range of process parameters such as ball-milling time and ball-to-powder ratio. The effect of process parameters on the physical and electrochemical properties of the LiFePO4/C composite was then discussed through the results of X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), the Brunauer-Emmet-Teller (BET) method and the use of an electrochemical cell of Li|1 M LiClO4 in EC:DEC = 1:1|LiFePO4. The carbon-coated LiFePO4 nanoparticles were prepared at 500 °C by SP and then milled at a rotating speed of 800 rpm, a ball-to-powder ratio of 40/0.5 and a ball-milling time of 3 h in an Ar atmosphere followed by heat treatment at 600 °C for 4 h in a N2 + 3% H2 atmosphere. SEM observation revealed that the particle size of LiFePO4 was significantly affected by the process parameters. Furthermore, TEM observation revealed that the LiFePO4 nanoparticles with a geometric mean diameter of 146 nm were coated with a thin carbon layer of several nanometers by the present method. Electrochemical measurement demonstrated that cells containing carbon-coated LiFePO4 nanoparticles could deliver markedly improved battery performance in terms of discharge capacity, cycling stability and rate capability. The cells exhibited first discharge capacities of 165 mAh g−1 at 0.1 C, 130 mAh g−1 at 5 C, 105 mAh g−1 at 20 C and 75 mAh g−1 at 60 C with no capacity fading after 100 cycles. 相似文献
13.
Hui-ping Liu Zhi-xing WangXin-hai Li Hua-jun GuoWen-jie Peng Yun-he ZhangQi-yang Hu 《Journal of power sources》2008
LiFePO4/C composite cathode material was prepared by carbothermal reduction method, which uses NH4H2PO4, Li2CO3 and cheap Fe2O3 as starting materials, acetylene black and glucose as carbon sources. The precursor of LiFePO4/C was characterized by differential thermal analysis and thermogravimetry. X-ray diffraction (XRD), scanning electron microscopy (SEM) micrographs showed that the LiFePO4/C is olivine-type phase, and the addition of the carbon reduced the LiFePO4 grain size. The carbon is dispersed between the grains, ensuring a good electronic contact. The products sintered at 700 °C for 8 h with glucose as carbon source possessed excellent electrochemical performance. The synthesized LiFePO4 composites showed a high electrochemical capacity of 159.3 mAh g−1 at 0.1 C rate, and the capacity fading is only 2.2% after 30 cycles. 相似文献
14.
A new water-soluble elastomer from ZEON Corp. was evaluated as binder with LiFePO4 cathode material in Li-ion batteries. The mechanical characteristic of this cathode was compared to that with PVdF-based cathode binder. The elastomer-based cathode shows high flexibility with good adhesion. The electrochemical performance was also evaluated and compared to PVdF-based cathodes at 25 and at 60 °C. A lower irreversible capacity loss was obtained with the elastomer-based cathode, however, aging at 60 °C shows a comparable cycle life to that observed with PVdF-based cathodes. The LiFePO4–WSB at high rate shows a good performance with 120 mAh g−1 at 10C rate at 60 °C. 相似文献
15.
Jun-chao Zheng Zhi-xing Wang De-rong Liu Ling-jun Li Hua-jun Guo 《Journal of power sources》2010,195(9):2935-2938
LiFePO4-Li3V2(PO4)3 composite cathode material is synthesized by aqueous precipitation of FeVO4·xH2O from Fe(NO3)3 and NH4VO3, following chemical reduction and lithiation with oxalic acid as the reducer and carbon source. Samples are characterized by XRD, SEM and TEM. XRD pattern of the compound synthesized at 700 °C indicates olivine-type LiFePO4 and monoclinic Li3V2(PO4)3 are co-existed. TEM image exhibits that LiFePO4-Li3V2(PO4)3 particles are encapsulated with a carbon shell 5-10 nm in thickness. The LiFePO4-Li3V2(PO4)3 compound cathode shows good electrochemical performance, and its discharge capacity is about 139.1 at 0.1 C, 135.5 at 1 C and 116 mA h g−1 at 3 C after 30 cycles. 相似文献
16.
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
17.
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
18.
A new type of LiFePO4/C composite surrounded by a web containing both amorphous and crystalline carbon phases was synthesized by incorporating malonic acid as a carbon source using a high temperature solid-state method. SEM, TEM/SAED/EDS and HRTEM were used to analyze surface morphology and confirmed for the first time that crystalline carbon was present in LiFePO4/C composites. The composite was effective in enhancing the electrochemical properties such as capacity and rate capability, because its active component consists of nanometer-sized particles containing pores with a wide range of sizes. An EDS elemental map showed that carbon was uniformly distributed on the surface of the composite crystalline particles. TEM/EDS results clearly show a dark region that is LiFePO4 with a trace of carbon and a gray region that is carbon only. To evaluate the materials’ electrochemical properties, galvanostatic cycling and conductivity measurements were performed. The best cell performance was delivered by the material coated with 60 wt.% malonic acid, which delivered first cycle discharge capacity of 149 mAh g−1 at a C/5 rate and sustained 222 cycles at 80% of capacity retention. When carboxylic acid was used as a carbon source to produce LiFePO4, overall conductivity increased from 10−5 to 10−4 S cm−1, since particle growth was prevented during the final sintering process. 相似文献
19.
Matthieu DubarryBor Yann Liaw Mao-Sung ChenSain-Syan Chyan Kuo-Chang HanWun-Tong Sie She-Huang Wu 《Journal of power sources》2011,196(7):3420-3425
Large format LiFePO4-based Li-ion batteries are rapidly becoming available from commercial cell manufacturers. In this paper two types of 10 Ah single cells (one prismatic and another cylindrical) from two manufacturers were tested at room temperature and 60 °C. Both cells suffered severe degradation at 60 °C. The results were analyzed using incremental capacity analysis (ICA) along with other electrochemical techniques. Overall the two types of cells were similar in behavior, despite subtle differences in performance. This study shed some light on the degradation process associated with these two large format LiFePO4 cell designs with regard to thermal degradation at elevated temperatures. The analysis illustrates a unique capability of using ICA to differentiate cell performance and material utilization in different cell designs. 相似文献
20.
In this study, a solution method was employed to synthesize LiFePO4-based powders with Li3PO4 and Fe2P additives. The composition, crystalline structure, and morphology of the synthesized powders were investigated by using ICP-OES, XRD, TEM, and SEM, respectively. The electrochemical properties of the powders were investigated with cyclic voltammetric and capacity retention studies. The capacity retention studies were carried out with LiFePO4/Li cells and LiFePO4/MCMB cells comprised LiFePO4-based materials prepared at various temperatures from a stoichiometric precursor. Among all of the synthesized powders, the samples synthesized at 750 and 775 °C demonstrate the most promising cycling performance with C/10, C/5, C/2, and 1C rates. The sample synthesized at 775 °C shows initial discharge capacity of 155 mAh g−1 at 30 °C with C/10 rate. From the results of the cycling performance of LiFePO4/MCMB cells, it is found that 800 °C sample exhibited higher polarization growth rate than 700 °C sample, though it shows lower capacity fading rate than 700 °C sample. For Fe2P containing samples, the diffusion coefficient of Li+ ion increases with increasing amount of Fe2P, however, the sample synthesized at 900 °C shows much lower Li+ ion diffusion coefficient due to the hindrance of Fe2P layer on the surface of LiFePO4 particles. 相似文献