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1.
以活化的天然石墨为碳源,采用固相辅助回流法成功合成了双相碳改性的Li2FeSiO4复合材料。采用XRD、SEM、HRTEM和Raman光谱分析了Li2FeSiO4/(C+G)复合材料的物相、形貌及其微观结构;并研究了活化石墨用量对Li2FeSiO4/(C+G)复合材料的电化学性能的影响。结果表明:活化石墨以石墨微晶和无定形碳的形态共存于Li2FeSiO4/(C+G)材料中,活化石墨用量为5%时所得样品的首次放电容量较高(170.3mAh·g-1),循环50次后其容量保持率为88.7%,表现出了良好的电化学性能。  相似文献   

2.
以活化的天然石墨为碳源,采用固相辅助回流法成功合成了双相碳改性的Li2FeSiO4复合材料。采用XRD、SEM、HRTEM和Raman光谱分析了Li2FeSiO4/(C+G)复合材料的物相、形貌及其微观结构;并研究了活化石墨用量对Li2FeSiO4/(C+G)复合材料的电化学性能的影响。结果表明:活化石墨以石墨微晶和无定形碳的形态共存于Li2FeSiO4/(C+G)材料中,活化石墨用量为5%时所得样品的首次放电容量较高(170.3 mAh·g-1),循环50次后其容量保持率为88.7%,表现出了良好的电化学性能。  相似文献   

3.
Li2FeSiO4/C cathode materials have been prepared using the conventional solid-state method by varying the sintering temperature (650 °C, 700 °C and 750 °C), and the structure and electrochemical performance of Li2FeSiO4/C materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests, respectively. The results show that Li2FeSiO4 nano-crystals with a diameter of about 6–8 nm are inbedded in the amorphous carbon, and the Li2FeSiO4/C material obtained at 700 °C exhibits an initial discharge capacity of 195 mA?h g?1 at 1/16 C in the potential range of 1.5–4.8 V. The excellent electrochemical performance of Li2FeSiO4/C attributes to the improvement of conductivity and reduction of impurity by the optimization of the sintering temperature.  相似文献   

4.
The key parameters related to cathode materials for commercial use are a high specific capacity, good cycling stability, capacity retention at high current rates, as well as the simplicity of the synthesis process. This study presents a facile synthesis of a composite cathode material, Li2FeSiO4 with carbon, under extreme conditions: rapid heating, short dwell at 750 °C and subsequent quenching. The water-soluble polymer methylcellulose was used both as an excellent dispersing agent and a carbon source that pyrolytically degrades to carbon, thereby enabling the homogeneous deployment of the precursor compounds and the control of the Li2FeSiO4 particle growth from the earliest stage of processing. X-ray powder diffraction reveals the formation of Li2FeSiO4 nanocrystallites with a monoclinic structure in the P21/n space group (#14). The composite’s electrochemical performance as a cathode material in Li-ion batteries was examined. The influence of the amount of methylcellulose on the microstructural, morphological, conductive, and electrochemical properties of the obtained powders has been discussed. It has been shown that the overall electrochemical performance is improved with an increase of carbon content, through both the decrease of the mean particle diameter and the increase of electrical conductivity.  相似文献   

5.
First principles calculations are used to anticipate the electrochemistry of polyoxoanionic materials consisting of XO4 − yAy (A = F, N) groups. As an illustrative case, this work focuses on the effect of either N or F for O substitution upon the electrochemical properties of Li2FeSiO4. Within the Pmn21–Li2FeSiO4 structure, virtual models of Li2Fe22.5+SiO3.5N0.5 and Li1.5Fe2+SiO3.5F0.5 have been analyzed. We predict that the lithium deinsertion voltage associated to the Fe3+/Fe4+ redox couple is decreased by both substituents. The high theoretical specific capacity of Li2FeSiO4 (330 mAh/g) could be retained in N-substituted silicates thanks to the oxidation of N3− anions, whilst Li1.5Fe2+SiO3.5F0.5 has a lower specific capacity inherent to the F substitution. Substitution of N/F for O will respectively improve/worsen the electrode characteristics of Li2FeSiO4.  相似文献   

6.
Dou  Junqing  Kang  Xueya  Wumaier  Tuerdi  Hua  Ning  Han  Ying  Xu  Guoqing 《Journal of Solid State Electrochemistry》2012,16(5):1925-1931
LiFePO4/C composite is synthesized by oxalic acid-assisted rheological phase method. Fe2O3 and LiH2PO4 are chosen as the starting materials, sucrose as carbon sources, and oxalic acid as the additive. The crystalline structure and morphology of the products are characterized by X-ray diffraction and field emission scanning electron microscopy. The charge–discharge kinetics of LiFePO4 electrode is investigated using cyclic voltammetry and electrochemical impedance spectroscopy. It is found that the introduction of appropriate amount of oxalic acid leads to smaller particle sizes, more homogeneous size distribution, and some Fe2P produced in the final products, resulting in reduced polarization, impedance, and improved Li+ ion diffusion coefficient. The best cell performance is delivered by the sample with R = 1.5 (R of the molar ratio of oxalic acid to LiH2PO4). Its discharge capacity is 154 mAh g−1 at 0.2 C rate and 120 mAh g−1 at 5.0 C rate. At the same time, it exhibits an excellent cycling stability; no obvious decrease even after 1,000 cycles at 1.0 C rate.  相似文献   

7.
The macroporous Li3V2(PO4)3/C composite was synthesized by oxalic acid-assisted carbon thermal reaction, and the common Li3V2(PO4)3/C composite was also prepared for comparison. These samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and electrochemical performance tests. Based on XRD and SEM results, the sample has monoclinic structure and macroporous morphology when oxalic acid is introduced. Electrochemical tests show that the macroporous Li3V2(PO4)3/C sample has a high initial discharge capacity (130 mAh g−1 at 0.1 C) and a reversible discharge capacity of 124.9 mAh g−1 over 20 cycles. Moreover, the discharge capacity of the sample is still 91.5 mAh g−1, even at a high rate of 2 C, which is better than that of the sample with common morphology. The improvement in electrochemical performance should be attributed to its improved lithium ion diffusion coefficient for the macroporous morphology, which was verfied by cyclic voltammetry and electrochemical impedance spectroscopy.  相似文献   

8.
采用湿法球磨和原位热解碳包覆相结合的方法, 分别以硬脂酸、柠檬酸、聚乙二醇-6000 (PEG-6000)、β-环糊精为碳源, 制备了不同结构的Na2MnPO4F/C 复合材料, 并研究了它们作为锂离子电池正极材料的电化学行为. 通过X射线衍射(XRD)、扫描电镜(SEM)、BET比表面积测试、恒流充放电等表征手段, 比较和分析了产物的结构、形貌及电化学性能. 研究结果表明, 由不同碳源制备的材料在形貌和颗粒尺寸上有明显差异, 进而对它们的电化学性能造成很大影响. 影响电化学性能的关键因素在于材料一次颗粒的大小. 其中, 以柠檬酸为碳源制备的样品呈现出典型的微纳结构和最小的一次颗粒(10-40 nm). 并给出最佳的电化学性能: 在1.5-4.8 V电压范围内, 以5 mA·g-1充放电电流获得的首次放电比容量约为80 mAh·g-1, 且循环稳定性良好.  相似文献   

9.
Natural graphite treated by mechanical activation can be directly applied to the preparation of Li3V2(PO4)3. The carbon-coated Li3V2(PO4)3 with monoclinic structure was successfully synthesized by using natural graphite as carbon source and reducing agent. The amount of activated graphite is optimized by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectrum, galvanostatic charge/discharge measurements, cyclic voltammetry, and electrochemical impedance spectroscopy tests. Our results show that Li3V2(PO4)3 (LVP)-10G exhibits the highest initial discharge capacity of 189 mAh g?1 at 0.1 C and 162.9 mAh g?1 at 1 C in the voltage range of 3.0–4.8 V. Therefore, natural graphite is a promising carbon source for LVP cathode material in lithium ion batteries.  相似文献   

10.
The flake-like Li3V2(PO4)3/C has been successfully synthesized by rheological phase method using polyvinyl alcohol (PVA) as template; the Li3V2(PO4)3/C without PVA assistance has been prepared for comparison. X-ray diffraction analysis shows that the two samples are well crystallized, and no impurity phases are detected. The scanning electron microscopy results reveal that there is a significant difference in morphologies between PVA-assisted sample and sample without PVA; the former shows a flake-like morphology, while the latter presents regular granular shape with some agglomeration. Transmission electron microscopy images reveal that Li3V2(PO4)3 particles are coated with a uniform surface carbon layer. The lattice fringes with a spacing of 0.428 nm can be clearly seen from the high-resolution transmission electron microscopy image. The PVA-assisted sample shows a discharge capacity of 120, 110, and 96 mAh g?1 at 1 C, 20 C, and 50 C, respectively; however, the sample without PVA exhibits a lower discharge capacity. Based on the analysis of electrochemical impedance spectroscopy, the lithium ion diffusion coefficients of Li3V2(PO4)3/C and PVA-assisted Li3V2(PO4)3/C are 4.19?×?10?9 and 4.99?×?10?8 cm2 s?1, respectively. In summary, it is demonstrated that using PVA as a template can obtain flake-like morphology and significantly improve the comprehensive electrochemical performances of Li3V2(PO4)3/C cathode material.  相似文献   

11.
As a kind of lithium-ion battery cathode material, monoclinic lithium vanadium phosphate/carbon Li3V2(PO4)3/C was synthesized by adopting phenolic resin as carbon source, both for reducing agent and coating material. The crystal structure and morphology of the samples were characterized through X-ray diffraction (XRD) and scanning electron microscope (SEM). Galvanostatic charge-discharging experiments and electrochemical impedance spectrum (EIS) were utilized to determine the electrochemical insertion properties of the samples. XRD data revealed that phenolic resin does not change the crystal structure of Li3V2(PO4)3/C. Furthermore, the morphology of grains and the electronic conductivity of Li3V2(PO4)3/C were improved. Galvanostatic charge-discharging and EIS results showed that the optimal electrochemical properties and the minimum charge-transfer resistance of Li3V2(PO4)3/C can be reached when added by 5 wt.% of redundant carbon (except the carbon needed to reduce V5+ to V3+). The initial discharge capacity is 128.4 mAh g?1 at 0.2 C rate and 101.2 mAh g?1 at 5 C in the voltage range of 3.0~4.3 V.  相似文献   

12.
LiFePO4/C composites are prepared by using two types of carbon source: one using polymer (PAALi) and the other using sucrose. The physical characteristics of LiFePO4/C composites are investigated by X-ray diffraction), scanning electron microscopy, BET, laser particle analyzer, and Raman spectroscopy. Their electrochemical properties are characterized by cyclic voltammograms, constant current charge–discharge, and electrochemical impedance spectra. These analyses indicate that the carbon source and carbon content have a great effect on the physical and electrochemical performances of LiFePO4/C composites. An ideal carbon source and appropriate carbon content can effectively increase the lithium-ion diffusion coefficient and exchange current density, decrease the charge transfer resistance (R ct), and enhance the electrochemical performances of LiFePO4/C composite. The results show that PAALi is a better carbon source for the synthesis of LiFePO4/C composites. When the carbon content is 4.11 wt.% (the molar ratio of PAALi/Li2C2O4 was 2:1), as-prepared LiFePO4/C composite shows the best combination between electrochemical performances and tap density.  相似文献   

13.
以月桂酸为碳源和表面活性剂,氢氧化锂、碳酸锂和醋酸锂为锂源,采用流变相法制备LiFePO4/C复合材料。运用X射线衍射(XRD)、扫描电子显微镜(SEM)、粒度分析、恒流充放电测试、循环伏安以及交流阻抗测试等方法对复合材料进行表征。结果表明,不同的锂源对LiFePO4/C复合材料的结构和电化学性能均有很大影响,以氢氧化锂为锂源合成的LiFePO4/C材料展示出最佳的循环性能和倍率性能。该材料在0.1C下放电比容量为153.4 mAh.g-1,在大倍率10 C下,容量保持率仍可达76%,甚至10C下循环800次后,容量衰减率仅有4%,SEM结果显示该材料具有较小的粒径(~200 nm),且分布集中,有效提高了电子迁移速率,从而改进了LiFePO4/C的倍率性能。  相似文献   

14.
Different approaches to synthesis of Li2FeSiO4-based electrode materials for lithium intercalation, using low-cost and abundant Li-, Si-, and Fe-containing parent substances, are discussed. XRD, SEM, and a laser-diffraction analyzer of particle size were used for structure and morphology characterization of the composite electrode materials. Li2FeSiO4 was shown to be the main lithium-accumulating crystalline phase; minor LiFeO2 and Li2SiO3 admixtures are also present. The material microparticles’ average size was shown to vary from tenths of micrometer to 1 μm. Larger objects sized ca. 2–4 μm are the microparticles’ agglomerates. The material electrochemical properties were studied by dc chronopotentiometry (galvanostatic charging–discharging) and cyclic voltammetry with potential linear sweeping. The initial reversible cycled capacity of the best samples is 170 mA h/g. The anodic and cathodic processes manifest obvious hysteresis caused by the presence of several different lithium ion energy states in the material; the transition between the states is kinetically hindered. The dependences of the specific capacity and its stability under cycling on the current load and the conductive carbon component content in the composite were elucidated.  相似文献   

15.
以V2O5、NH4H2PO4、LiOH、柠檬酸、三嵌段聚合物表面活性剂P123为原料, 用流变相(RPR)法制备了Li3V2(PO4)3/C正极材料. 用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)等方法表征, 结果表明: 材料为单一纯相的单斜晶体结构, 颗粒均匀并呈现珊瑚结构; 恒流充放电, 循环伏安(CV)及电化学交流阻抗(EIS)等电化学性能测试表明, 采用P123 辅助合成材料电化学性能明显优于未采用P123 辅助合成材料. 3.0-4.3 V放电区间, 0.1C充放电下P123 辅助合成Li3V2(PO4)3/C材料首次放电比容量为129.8 mAh·g-1, 经过50 次循环后容量只衰减0.9%; 倍率性能及循环性能优异, 1C、10C、25C的首次放电比容量分别为128.2、121.3、109.1 mAh·g-1, 50次循环后容量保持率分别为99.1%, 96.9%, 90.7%. 这归因于三嵌段聚合物P123 作为分散剂的同时也作为有机碳源在颗粒表面及间隙形成碳网络, 有利于材料导电率的改善, 降低了其电荷转移阻抗, 减小了电极充放电过程的极化现象.  相似文献   

16.
A series of Li3V2(PO4)3/C composites with different amounts of carbon are synthesized by a combustion method. The physical and electrochemical properties of the Li3V2(PO4)3/C composites are investigated by X-ray diffraction, element analysis, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and electrochemical measurements. The effects of carbon content of Li3V2(PO4)3/C composites on its electrochemical properties are conducted with cyclic voltammetry and electrochemical impedance. The experiment results clearly show that the optimal carbon content is 4.3 wt %, and more or less amount of carbon would be unfavorable to electrochemical properties of the Li3V2(PO4)3/C electrode materials. The results would provide some basis for further improvement on the Li3V2(PO4)3 electrode materials.  相似文献   

17.
Li2ZnTi3O8/C nanocomposite has been synthesized using phenolic resin as carbon source in this work. The structure, morphology, and electrochemical properties of the as-prepared Li2ZnTi3O8 samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), Raman spectroscopy (RS), galvanostatic charge–discharge, and AC impedance spectroscopy. SEM images show that Li2ZnTi3O8/C was agglomerated with a primary particle size of ca. 40 nm. TEM images reveal that a homogeneous carbon layer (ca. 5 nm) formed on the surface of Li2ZnTi3O8 particles which is favorable to improve the electronic conductivity and inhibit the growth of Li2ZnTi3O8 during annealing process. The as-prepared Li2ZnTi3O8/C composite with 6.0 wt.% carbon exhibited a high initial discharge capacity of 425 and 159 mAh g?1 at 0.05 and 5 A g?1, respectively. At a high current density of 1 A g?1, 95.5 % of its initial value is obtained after 100 cycles.  相似文献   

18.
LiFePO4 samples have been synthesized by mixing stoichiometric amounts of (NH4)2HPO4, FeC2O4·2H2O, and LiF. During synthesis, carbon gel was used as the carbon source. Single-phase LiFePO4 can be formed when the heating temperature ranges from 650 to 800 °C and it is decomposed into Li4P2O7, Li3PO4, Fe2P, and Li3P7 when the temperature comes to 850 °C. We find that the ratio of the lattice parameter (a/c) decreases with the increasing temperature, thereby increasing the Li+ diffusion channel length. Both the decrease of a/c and the abrupt crystal growth are expected to contribute to the monotonic decrease of the initial capacity of the samples. The sample heated at 650 °C with a smaller uniform particle size and relative higher specific surface area (8.2 m2/g) shows an excellent electrochemical performance. The initial specific capacity of 156.7(3) mAh/g is obtained at the rate of C/10.  相似文献   

19.
Spinel Li4Mn5O12 nanoparticles are successfully prepared by water-in-oil microemulsion method and characterized by X-ray diffraction and scanning electron microscopy. The Li4Mn5O12 nanoparticles have sphere-like morphology with particle size less than 50 nm. The Li4Mn5O12 and activated carbon (AC) were used as electrodes of Li4Mn5O12/AC supercapacitor, respectively. The electrochemical capacitance performance of the supercapacitor was investigated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The results showed that the single electrode was able to deliver specific capacitance 252 F g?1 within potential range 0–1.4 V at a scan rate of 5 mV s?1 in 1 mol L?1 Li2SO4 solution, and it also showed high coulombic efficiency close to 100%. This material exhibited a good cycling performance.  相似文献   

20.
使用Nb2O5和Nb(OC6H5)5为铌源对LiFePO4/C中的锂位和铁位分别掺杂,采用碳热还原法合成掺杂Nb的磷酸铁锂系列材料。运用X射线衍射仪、扫描电镜、循环伏安、交流阻抗谱和恒电流充放电测试等对材料进行表征。结果表明:相比掺杂位置,铌源对材料的颗粒形貌和粒径分布影响更大,而颗粒大小对材料的电化学性能,尤其是大倍率性能的提高有重要作用;掺杂在Li位的Nb元素比在Fe位能更好的稳定晶体结构,从而有利于提高循环性能。  相似文献   

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