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1.
Several 1-alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids (alkyl-DMimTFSI) were prepared by changing carbon chain lengths and configuration of the alkyl group, and their electrochemical properties and compatibility with Li/LiFePO4 battery electrodes were investigated in detail. Experiments indicated the type of ionic liquid has a wide electrochemical window (−0.16 to 5.2 V vs. Li+/Li) and are theoretically feasible as an electrolyte for batteries with metallic lithium as anode. Addition of vinylene carbonate (VC) improves the compatibility of alkyl-DMimTFSI-based electrolytes towards lithium anode and LiFePO4 cathode, and enhanced the formation of solid electrolyte interface to protect lithium anodes from corrosion. The electrochemical properties of the ionic liquids obviously depend on carbon chain length and configuration of the alkyl, including ionic conductivity, viscosity, and charge/discharge capacity etc. Among five alkyl-DMimTFSI-LiTFSI-VC electrolytes, Li/LiFePO4 battery with the electrolyte-based on amyl-DMimTFSI shows best charge/discharge capacity and reversibility due to relatively high conductivity and low viscosity, its initial discharge capacity is about 152.6 mAh g−1, which the value is near to theoretical specific capacity (170 mAh g−1). Although the battery with electrolyte-based isooctyl-DMimTFSI has lowest initial discharge capacity (8.1 mAh g−1) due to relatively poor conductivity and high viscosity, the value will be dramatically added to 129.6 mAh g−1 when 10% propylene carbonate was introduced into the ternary electrolyte as diluent. These results clearly indicates this type of ionic liquids have fine application prospect for lithium batteries as highly safety electrolytes in the future. 相似文献
2.
Andrzej Lewandowski Agnieszka ?widerska-Mocek Ilona Acznik 《Electrochimica acta》2010,55(6):1990-10350
LiMn2O4 was examined as a cathode material for lithium-ion batteries, working together with a room temperature ionic liquid electrolyte, obtained by dissolution of solid lithium bis(trifluoromethanesulfonyl)imide (LiNTf2) in liquid N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (MePrPipNTf2), with the formation of a liquid LiNTf2-MePrPipNTf2 system. The Li/LiMn2O4 cell was tested by galvanostatic charging/discharging and by impedance spectroscopy. The LiMn2O4 cathode showed good cyclability and Coulombic efficiency in the presence of 10 wt.% of vinylene carbonate (VC) as an additive to the ionic liquid. The flash point of the LiNTf2-MePrPipNTf2-VC(10%) electrolyte was estimated to be above 300 °C. 相似文献
3.
The capacity loss rate of LiFePO4 in aqueous electrolyte was found to be much faster than it in organic electrolyte. The cycling stability in aqueous electrolyte with various dissolved oxygen content and pH value was extensively studied by cyclic voltammetry. It was found that both high OH− and dissolve O2 content can accelerate the cycling fading of LiFePO4. It has been proved that the capacity fading of LiFePO4 is due to not only chemical instability but also electrochemical instability. Mössbauer spectroscopy demonstrated that the Fe(III)-containing species was formed in the active materials arisen from the irreversible side reaction. The carbon-coated LiFePO4 prepared by chemical vapor decomposition method shows significantly improvement in cycling stability. The carbon coating technology provides an effective approach to enhance cycling performance in aqueous electrolyte as well as proof of proposed fading mechanism. 相似文献
4.
Andrzej Lewandowski Beata Kurc Izabela Stepniak Agnieszka Swiderska-Mocek 《Electrochimica acta》2011,(17):5972
Sulfolane (also referred to as tetramethylene sulfone, TMS) containing LiPF6 and vinylene carbonate (VC) was tested as a non-flammable electrolyte for a graphite |LiFePO4 lithium-ion battery. Charging/discharging capacity of the LiFePO4 electrode was ca. 150 mAh g−1 (VC content 5 wt%). The capacity of the graphite electrode after 10 cycles establishes at the level of ca. 350 mAh g−1 (C/10 rate). In the case of the full graphite |1 M LiPF6 + TMS + VC 10 wt% |LiFePO4 cell, both charging and discharging capacity (referred to cathode mass) stabilized at a value of ca. 120 mAh g−1. Exchange current density for Li+ reduction on metallic lithium, estimated from electrochemical impedance spectroscopy (EIS) experiments, was jo(Li/Li+) = 8.15 × 10−4 A cm−2. Moreover, EIS suggests formation of the solid electrolyte interface (SEI) on lithium, lithiated graphite and LiFePO4 electrodes, protecting them from further corrosion in contact with the liquid electrolyte. Scanning electron microscopy (SEM) images of pristine electrodes and those taken after electrochemical cycling showed changes which may be interpreted as a result of SEI formation. No graphite exfoliation was observed. The main decomposition peak of the LiPF6 + TMS + VC electrolyte (TG/DTA experiment) was present at ca. 275 °C. The LiFePO4(solid) + 1 M LiPF6 + TMS + 10 wt% VC system shows a flash point of ca. 150 °C. This was much higher in comparison to that characteristic of a classical LiFePO4 (solid) + 1 M LiPF6 + 50 wt% EC + 50 wt% DMC system (Tf ≈ 37 °C). 相似文献
5.
In this work, we examined the electrochemical behaviour of lithium ion batteries containing lithium iron phosphate as the positive electrode and systems based on Li-Al or Li-Ti-O as the negative electrode. These two systems differ in their potential versus the redox couple Li+/Li and in their morphological changes upon lithium insertion/deinsertion. Under relatively slow charge/discharge regimes, the lithium-aluminium alloys were found to deliver energies as high as 438 Wh kg−1 but could withstand only a few cycles before crumbling, which precludes their use as negative electrodes. Negative electrodes consisting solely of aluminium performed even worse. However, an electrode made from a material with zero-strain associated to lithium introduction/removal such as a lithium titanate spinel exhibited good performance that was slightly dependent on the current rate used. The Li4Ti5O12/LiFePO4 cell provided capacities as high as 150 mAh g−1 under C-rate in the 100th cycle. 相似文献
6.
Improved electrochemical performance of LiFePO4 by increasing its specific surface area 总被引:1,自引:0,他引:1
Yonggao Xia 《Electrochimica acta》2006,52(1):240-245
Cathode material LiFePO4 with an excellent rate capability has been successfully prepared by a simple solid state reaction method using LiCH3COO·2H2O, FeC2O4·2H2O and (NH4)2HPO4 as the starting materials. We have investigated the effects of the sintering temperature and mixing time of the starting materials on the physical properties and electrochemical performance of LiFePO4. It was found that the rate capability of LiFePO4 is mainly controlled by its specific surface area and it is an effective way to improve the rate capability of the sample by increasing its specific surface area. In the present study, our prepared LiFePO4 with a high specific surface area of 24.1 m2 g−1 has an excellent rate capability and can deliver 115 mAh g−1 of reversible capacity even at the 5 C rate. Moreover, we have prepared lithium ion batteries based on LiFePO4 as the cathode material and MCMB as the anode material, which showed an excellent cycling performance. 相似文献
7.
Yan Cui 《Electrochimica acta》2010,55(3):922-7735
Carbon coated LiFePO4 particles were first synthesized by sol-gel and freeze-drying method. These particles were then coated with La0.7Sr0.3MnO3 nanolayer by a suspension mixing process. The La0.7Sr0.3MnO3 and carbon co-coated LiFePO4 particles were calcined at 400 °C for 2 h in a reducing atmosphere (5% of hydrogen in nitrogen). Nanolayer structured La0.7Sr0.3MnO3 together with the amorphous carbon layer forms an integrate network arranged on the bare surface of LiFePO4 as corroborated by high-resolution transmission electron microscopy. X-ray diffraction results proved that the co-coated composite still retained the structure of the LiFePO4 substrate. The twin coatings can remarkably improve the electrochemical performance at high charge/discharge rates. This improvement may be attributed to the lower charge transfer resistance and higher electronic conductivity resulted from the twin nanolayer coatings compared with the carbon coated LiFePO4. 相似文献
8.
Ho Chul Shin Sung Bin Park Kyung Yoon Chung Chang Sam Kim 《Electrochimica acta》2008,53(27):7946-7951
Structural change of Cr-doped LiFePO4/C during cycling is investigated using conventional and synchrotron-based in situ X-ray diffraction techniques. The carbon-coated and Cr-doped LiFePO4 particles are synthesized by a mechanochemical process followed by a one-step heat treatment. The LiFe0.97Cr0.03PO4/C has shown excellent rate performance, delivering the discharge capacity up to 120 mAh/g at 10 C rate. The results suggest that the improvement of the rate performance is attributed to the chromium doping, which facilitates the phase transformation between triphylite and heterosite during cycling, and conductivity improvement by carbon coating. Structural analysis using the synchrotron source also indicates that the doped Cr replaces Fe and/or Li sites in LiFePO4. 相似文献
9.
LiFePO4/C composite cathode materials with carbon nano-interconnect structures were synthesized by one-step solid state reaction using low-cost asphalt as both carbon source and reducing agent. Based on the thermogravimetry, differential scanning calorimetry, transmission electron microscopy and high-resolution transmission electron microscopy, a growth model was proposed to illustrate the formation of the carbon nano-interconnect between the LiFePO4 grains. The LiFePO4/C composite shows enhanced discharge capacity (150 mAh g−1) with excellent capacity retention compared with the bare LiFePO4 (41 mAh g−1) due to the electronically conductive nanoscale networking provided by the asphalt-based carbon. The results prove that the asphalt is a perfect carbon source and reduction agent for cost-effective production of high performance LiFePO4/C composite. 相似文献
10.
Amorphous hydrated iron (III) phosphate has been synthesized by a coordinate precipitation method from equimolecular Fe(NO3)3 and (NH4)2HPO4 solutions at an elevated temperature. Hydrated iron (III) phosphate samples and the corresponding LiFePO4/C products were characterized by XRD and SEM. The electrochemical behavior was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The LiFePO4/C fabricated from as-synthesized FePO4 delivered discharge capacities of 162.5, 147.3, 133.0, 114.7, 97.2, 91.3 and 88.5 mAh g−1 at rates of 0.1C, 0.2C, 0.5C, 1C, 2C, 3C and 4C with satisfactory capacity retention, respectively. 相似文献
11.
A water quenching (WQ) method was developed to synthesize LiFePO4 and C-LiFePO4. Our results indicate that this synthesis method ensures improved electrochemical activity and small crystal grain size. The synthetic conditions were optimized using orthogonal experiments. The LiFePO4 sample prepared at the optimized condition showed a maximum discharge capacity of 149.8 mAh g−1 at a C/10 rate. C-LiFePO4 with a low carbon content of 0.93% and a high discharge specific capacity of 163.8 mAh g−1 has also been obtained using this method. Water quenching treatment shows outstanding improvement of the electrochemical performance of LiFePO4. 相似文献
12.
Yoshihiro Kadoma 《Electrochimica acta》2010,55(3):1034-10166
LiFePO4 can be used as a positive electrode material for lithium-ion batteries by making composite with electrical conductive carbonaceous materials. In this study, LiFePO4/C (carbon) composite was prepared by a soft chemistry route, in which sucrose was used as a carbon source of a low price. We tried to optimize a Li/(LiFePO4/C) cell performance through changing synthetic conditions and discussed the factors affecting the electrochemical performances of the cell, such as the amount of the carbon source, synthetic temperature, gas flow rate of pyrolysis and the formation of secondary phases. It was found that the connection of the residual carbon and Fe2P to LiFePO4 particles and the amount of these two phases were important factors. In our experimental conditions, LiFePO4/C including 9.72 wt.% of residual carbon, prepared at 800 °C for 12 h showed the highest reversible capacity and the best C rate performance among the synthesized materials; 130 mAh g−1 at 10C rate and 50 °C. 相似文献
13.
Pure, nano-sized LiFePO4 and LiFePO4/C cathode materials are synthesized by spray-drying and post-annealing method. The influence of the sintering temperature and carbon coating on the structure, particle size, morphology and electrochemical performance of LiFePO4 cathode material is investigated. The optimum processing conditions are found to be thermal treatment for 10 h at 600 °C. Compared with LiFePO4, LiFePO4/C particles are smaller in size due to the inhibition of crystal growth to a great extent by the presence of carbon in the reaction mixture. And that the LiFePO4/C composite coated with 3.81 wt.% carbon exhibits the best electrode properties with discharge capacities of 139.4, 137.2, 133.5 and 127.3 mAh g−1 at C/5, 1C, 5C and 10C rates, respectively. In addition, it shows excellent cycle stability at different current densities. Even after 50 cycles at the high current density of 10C, a discharge capacity of 117.7 mAh g−1 is obtained (92.4% of its initial value) with only a low capacity fading of 0.15% per cycle. 相似文献
14.
LiFePO4/carbon composite cathode material was prepared using polyvinyl alcohol (PVA) as carbon source by pelleting and subsequent pyrolysis in N2. The samples were characterized by XRD, SEM and TGA. Their electrochemical performance was investigated in terms of charge–discharge cycling behavior. It consists of a single LiFePO4 phase and amorphous carbon. The special micro-morphology via the process is favorable for electrochemical properties. The discharge capacity of the LiFePO4/C composite was 145 mAh/g, closer to the theoretical specific capacity of 170 mAh/g at 0.1 C low current density. At 3 C modest current density, the specific capacity was about 80 mAh/g, which can satisfy for transportation applications if having a more planar discharge flat. 相似文献
15.
Ho Chul Shin Kyung Wan Nam Won Young Chang Byung Won Cho Won-Sub Yoon Xiao-Qing Yang Kyung Yoon Chung 《Electrochimica acta》2011,(3):1182
The structural changes of LiFePO4 and C-coated LiFePO4 during charging at various C-rates and temperatures are investigated using synchrotron based in situ X-ray diffraction technique. The XRD patterns collected during cycling show the structural evidence of the positive effects of carbon coating on LiFePO4 for the electrochemical performance improvements at different temperatures, especially at low temperatures. At −10 °C, the C-coated LiFePO4 shows comparable capacities with the sample cycled at room temperature when cycled at C/5 rate with a slight shift of the plateau to a higher voltage during charging. The in situ XRD patterns collected simultaneously show a complete phase transformation from triphylite to heterosite. At −20 °C, the C-coated LiFePO4 delivers 55.6% of its theoretical capacities at C/5 rate. However, the plateau in the charging curve becomes sloppy and shifts to a higher voltage. The in situ XRD patterns show that the phase transformation from triphylite to heterosite is not completed when charged to 4.5 V due to the larger polarization when charged at −20 °C. 相似文献
16.
The electroactive LiFePO4/C nano-composite has been synthesized by an emulsion drying method. During burning-out the oily emulsion precipitates in an air-limited atmosphere at 300 °C, amorphous or low crystalline carbon was generated along with releasing carbon oxide gases, and trivalent iron as a cheap starting material was immediately reduced to the divalent one at this stage as confirmed by X-ray photoelectron spectroscopy, leading to a low crystalline LiFePO4/C composite. Heat-treatment of the low crystalline LiFePO4/C in an Ar atmosphere resulted in a well-ordered olivine structure, as refined by Rietveld refinement of the X-ray diffraction pattern. From secondary electron microscopic and scanning transmission electron microscopic observations with the corresponding elemental mapping images of iron and phosphorous, it was found that the LiFePO4 powders are modified by fine carbon. The in situ formation of the nano-sized carbon during crystallization of LiFePO4 brought about two advantages: (i) an optimized particle size of LiFePO4, and (ii) a uniform distribution of fine carbon in the product. These effects of the fine carbon on LiFePO4/C composite led to high capacity retention upon cycling at 25 and 50 °C and high rate capability, resulting from a great enhancement of electric conductivity as high as 10−4 S cm−1. That is, the obtained capacity was higher than 90 mAh (g-phosphate)−1 by applying a higher current density of about 1000 mA g−1 (11 C) at 50 °C. 相似文献
17.
LiFePO4/(Ag + C) composite cathodes with a new type of nano-sized carbon webs were synthesized by two methods of an aqueous co-precipitation and a sol-gel process, respectively. Simultaneous thermogravimetric-differential thermal analysis indicates that the crystallization temperature of LiFePO4 is about 455-466 °C, which is close to the pyrolysis temperature of polypropylene, 460 °C. The silver and carbon co-modifying does not affect the olivine structure of LiFePO4 but improves its kinetics in terms of discharge capacity and rate capability. Discharge capacities were improved from 153.4 mA h g− 1 of LiFePO4/C to 160.5 mA h g− 1and 162.1 mA h g− 1 for LiFePO4/(Ag + C) cathodes synthesized by the co-precipitation and sol-gel methods, respectively. The possible reasons for the small difference in discharge capacity of two LiFePO4/(Ag + C) cathodes were discussed. AC impedance measurements show that the Ag + C co-modification decreases the charge transfer resistance of LiFePO4/(Ag + C) cathodes. 相似文献
18.
Synthesis and characterization of high-density LiFePO4/C composites as cathode materials for lithium-ion batteries 总被引:1,自引:0,他引:1
To achieve a high-energy-density lithium electrode, high-density LiFePO4/C composite cathode material for a lithium-ion battery was synthesized using self-produced high-density FePO4 as a precursor, glucose as a C source, and Li2CO3 as a Li source, in a pipe furnace under an atmosphere of 5% H2-95% N2. The structure of the synthesized material was analyzed and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical properties of the synthesized LiFePO4/carbon composite were investigated by cyclic voltammetry (CV) and the charge/discharge process. The tap-density of the synthesized LiFePO4/carbon composite powder with a carbon content of 7% reached 1.80 g m−3. The charge/discharge tests show that the cathode material has initial charge/discharge capacities of 190.5 and 167.0 mAh g−1, respectively, with a volume capacity of 300.6 mAh cm−3, at a 0.1C rate. At a rate of 5C, the LiFePO4/carbon composite shows a high discharge capacity of 98.3 mAh g−1 and a volume capacity of 176.94 mAh cm−3. 相似文献
19.
Bing Huang 《Electrochimica acta》2010,55(3):1227-391
A micron-sized LiFePO4/C composite with a spherical morphology was reduced carbothermally from precursor particles prepared by ball milling-assisted spray-drying. The specific capacity of the electrode at a 10 C (1700 mA/g) rate was 110 mAh/g and a high voltage plateau was achieved. The high-rate performance of the composite electrode was due to its unique spherical structure, comprising clusters of nano- or sub-micron-sized spherical particles. This morphology increases the effective conductive surface area, reduces the charge-transfer reaction resistance and improves the diffusion of lithium ions. 相似文献
20.
Chi-Lin Li 《Electrochimica acta》2008,53(22):6434-6443
Amorphous LiFe(WO4)2 thin films have been fabricated by radio-frequency (R.F.) sputtering deposition at room temperature. The as-deposited and electrochemically cycled thin films are, respectively, characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectra techniques. An initial discharge capacity of 198 mAh/g in Li/LiFe(WO4)2 cells is obtained, and the electrochemical behavior is mostly preserved in the following cycling. These results identified the electrochemical reactivity of two redox couples, Fe3+/Fe2+ and W6+/Wx+ (x = 4 or 5). The kinetic parameters and chemical diffusion coefficients of Li intercalation/deintercalation are estimated by cyclic voltammetry and alternate-current (AC) impedance measurements. All-solid-state thin film lithium batteries with Li/LiPON/LiFe(WO4)2 layers are fabricated and show high capacity of 104 μAh/cm2 μm in the first discharge. As-deposited LiFe(WO4)2 thin film is expected to be a promising positive electrode material for future rechargeable thin film batteries due to its large volumetric rate capacity, low-temperature fabrication and good electrode/electrolyte interface. 相似文献