Electrochemical Properties Of LiFePO Research Articles

Preparation and electrochemical properties of LiFePO 4/C composite with network structure for lithium ion batteries

The bare LiFePO 4 and LiFePO 4/C composites with network structure were prepared by solid-state reaction. The crystalline structures, morphologies and specific surface areas of the materials were investigated by X-ray difrractometry(XRD), scanning electron microscopy(SEM) and multi-point brunauer emmett and teller(BET) method. The results show that the LiFePO 4/C composite with the best network structure is obtained by adding 10% phenolic resin carbon. Its electronic conductivity increases to 2.86 × 10 −2 S/cm. It possesses the highest specific surface area of 115.65 m 2/g, which exhibits the highest discharge specific capacity of 164.33 mA·h/g at C/10 rate and 149.12 rnA·h/g at 1 C rate. The discharge capacity is completely recovered when C/10 rate is applied again.

High-rate properties of LiFePO 4/carbon composites as cathode materials for lithium-ion batteries

Electrochemical properties of LiFePO 4/carbon composites were investigated to achieve a high-rate lithium electrode performance. LiFePO 4/carbon composites were synthesized by a hydrothermal reaction of a solution of FeSO 4·7H 2O, H 3PO 4, and LiOH·H 2O mixed with carbon powders under nitrogen atmosphere followed by annealing under 1% H 2–99% Ar atmosphere. Particle size of the obtained LiFePO 4/carbon composites observed by scanning electron microscopy was less than 100 nm. At a high current density of 1000 mA g −1, the LiFePO 4/carbon composites showed a high discharge capacity of 113 mA h g −1, and a flat discharge potential plateau was observed around 3.4 V. The discharge capacity at the high current density, 85% of that at a low current density of 30 mA g −1, is a quite high value for LiFePO 4 cathodes. Homogeneous microstructure consisting of small particles contributed to the high-rate properties of the LiFePO 4/carbon composites.

Effects of fluorine-substitution on the electrochemical behavior of LiFePO 4/C cathode materials

The effects of fluorine substitution on the electrochemical properties of LiFePO 4/C cathode materials were studied. Samples with stoichiometric proportion of LiFe(PO 4) 1− x F 3 x /C ( x = 0.025, 0.05, 0.1) were prepared by adding LiF in the starting materials of LiFePO 4/C. XRD and XPS analyses indicate that LiF was completely introduced into bulk LiFePO 4 structure in LiFe(PO 4) 1− x F 3 x /C ( x = 0.025, 0.05) samples, while there was still some excess of LiF in LiFe(PO 4) 0.9F 0.3/C sample. The results of electrochemical measurement show that F-substitution can improve the rate capability of these cathode materials. The LiFe(PO 4) 0.9F 0.3/C sample showed the best high rate performance. Its discharge capacity at 10 C rate was 110 mAh g −1 with a discharge voltage plateau of 3.31–3.0 V versus Li/Li +. The LiFe(PO 4) 0.9F 0.3/C sample also showed obviously better cycling life at high temperature than the other samples.

Influence of Ti 4+ doping on electrochemical properties of LiFePO 4/C cathode material for lithium-ion batteries

To improve the performance of LiFePO 4, single phase Li 1-4 x Ti x FePO 4/C ( x=0, 0.005, 0.010, 0.015) cathodes were synthesized by solid-state method. A certain content of glucose was used as carbon precursor and content of carbon in every final product was about 3.5%. The samples were characterized by X-ray diffraction(XRD), scanning electron microscopy observations(SEM), charge/discharge test, carbon analysis and electrochemical impedance spectroscopy(EIS). The results indicate that the prepared samples have ordered olivine structure and doping of the low concentration Ti 4+ does not affect the structure of the samples. The electrochemical capabilities evaluated by charge-discharge test show that the sample with 1% Ti 4+ (molar fraction) has good electrochemical performance delivering about an initial specific capacity of 146.7 mAΔh/g at 0.3 C rate. Electrochemical impedance spectroscopy measurement results show that the charge transfer resistance of the sample could be decreased greatly by doping an appropriate amount Ti 4+.

Electrochemical properties of LiFePO 4 prepared via hydrothermal route

LiFePO 4 as a cathode material for rechargeable lithium batteries was prepared by hydrothermal process at 170 °C under inert atmosphere. The starting materials were LiOH, FeSO 4, and (NH 4) 2HPO 4. The particle size of the obtained LiFePO 4 was 0.5 μm. The electrochemical properties of LiFePO 4 were characterized in a mixed solvent of ethylene carbonate and diethyl carbonate (1:1 in volume) containing 1.0 mol dm −3 LiClO 4. The hydrothermally synthesized LiFePO 4 exhibited a discharge capacity of 130 mA h g −1, which was smaller than theoretical capacity (170 mA h g −1). The annealing of LiFePO 4 at 400 °C in argon atmosphere was effective in increasing the discharge capacity. The discharge capacity of the annealed LiFePO 4 was 150 mA h g −1.

Electrochemical properties of carbon-coated LiFePO 4 cathode using graphite, carbon black, and acetylene black

Electrochemical properties of LiFePO 4 were investigated by incorporating conductive carbon from three different carbon sources (graphite, carbon black, acetylene black). SEM observations revealed that the carbon-coated LiFePO 4 were smaller than the bare LiFePO 4 particles. The carbon-coated LiFePO 4 showed much better performance in terms of the discharge capacity and cycling stability than the bare LiFePO 4. Among carbon-coated LiFePO 4, the particles coated with graphite exhibited better electrochemical properties than others coated with carbon black or acetylene black.

Synthesis and electrochemical properties of olivine-type LiFePO 4/C composite cathode material prepared from a poly(vinyl alcohol)-containing precursor

Olivine structure LiFePO 4/C composite powders are synthesized as cathode materials for Li-ion batteries via a conventional solid-state reaction. Improvement in electrochemical performance has been achieved by using poly(vinyl alcohol) as the carbon sources for the as-prepared materials. The influence of the heat treatment on the physical and the electrochemical properties of LiFePO 4/C materials is investigated. To examine the effect of added carbon content on the properties of materials, a one-step heat treatment has been employed with control of the PVA content in the precursor. Six samples were prepared with 0, 1, 3, 5, 10 and 30 wt.% PVA added to the raw materials. The particle size of LiFePO 4 decreases as the carbon content increases. Materials with medium carbon contents have a small charge-transfer resistance and thus exhibit superior electrochemical performance. Interestingly, for a LiFePO 4/C composite with a low PVA content, an unusual plateau at 4.3 V is observed. It is considered that this is due to the Fe 3+/Fe 4+ redox reaction of Fe 3+ compounds that are present as an impurity. For samples with a high PVA amount, a thicker carbon coating provides an obstacle to improve the electrochemical properties.

Synthesis and effect of forming Fe 2P phase on the physics and electrochemical properties of LiFePO 4/C materials

Series LiFePO 4/C materials have been prepared by a so-called reformative solid-coordination method, which uses citric acid as the coordination agent and carbon source. A monodenate coordination band of –COO-M was proved to form gradually and that would help to disperse Li + or Fe 2+ among the homogeneous gel during the grinding process. Impure phase Fe 2P was detected out among the LiFePO 4/C composites with increasing annealed temperature. The remnant coating carbon was considered to be the reductive under the pure nitrogen gas. The amounts of carbon, particle size and morphology were investigated in detail and all the results showed to be related to the formation of Fe 2P. The electro-conductive Fe 2P phase among LiFePO 4/C composites acts as important role in increasing electronic conductivity and evidently improves the electrochemical performance of LiFePO 4/C including the less polarization phenomenon, comparatively high reversible capability, stable cycling performance and slight trend of less loss of rate capability.

Electrochemical properties of the carbon-coated LiFePO 4 as a cathode material for lithium-ion secondary batteries

In this study the effect of the carbon coating on the electrochemical properties of LiFePO 4 as a cathode for Li-ion batteries were investigated. The carbon-coated LiFePO 4 particles were synthesized by the mechanochemical process and one-step heat treatment. Microscopic observations using SEM and TEM revealed that the carbon coating reduced the particle size of the LiFePO 4. The carbon-coated LiFePO 4 showed much better performances in terms of the discharge capacity and cycle stability than bare LiFePO 4. It was confirmed that the carbon coating decreased the migration distance of Li-ion and enhanced the charge transfer from CV and ac impedance measurements. The improved electrochemical properties of the carbon-coated LiFePO 4 were, therefore, attributed to the reduced particle size and enhanced electrical contacts by carbon.

Effect of sintering time on the physical and electrochemical properties of LiFePO 4/C composite cathodes

LiFePO 4/C composite materials were synthesized at 700 °C by an in situ solid-state reaction. The effect of the sintering time on its structure, surface morphology and electrochemical performance was investigated by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), Raman spectroscopy analyses, cyclic voltammogram (CV), and galvanostatically charge–discharge techniques. It was found that, all prepared materials for various sintering time show the single olivine structure. The powder morphology change is negligible with extending sintering time from 5 to 40 h. Moreover, the I D/ I G ratio of carbon in Raman shift remains almost invariant (∼0.96) with the increase of sintering time. Electrochemical tests show that the discharge capacity remains at 153 mA h g −1 with medium-rate (0.5 C), while increases from about 120 to 130 mA h g −1 at high-rate (1 C) with increasing sintering time, and the possible reasons are discussed. The LiFePO 4/C composite synthesized at 700 °C for 30 h demonstrates a best electrochemical performance, delivering a discharge capacity of 110 mA h g −1 (1.5 C) after 50 cycles.

Effect of texture on the electrochemical properties of LiFePO 4 thin films

Carbon-free in situ crystallized LiFePO 4 thin films were grown using the Pulsed Laser Deposition (PLD) technique. Adjusting the deposition time enabled the growth of films with different thicknesses. Comparing the properties of these films ((120) preferentially oriented) highlighted a relationship between microstructure and electrochemical activity. However, whatever film thickness (from 12 nm to 600 nm), the capacities recorded were far from the ones expected, since only a small percentage of the film was found to really chemically or electrochemically react. Simple experiments (creation of surface defect, metal electrodeposition, AC/DC conductivity measurements, etc.) carried out on these films gave a new insight into the origin of the limitations. The results presented herein singularly lead to the conclusion that the ionic conductivity is the main limitation for such olivine-type thin films.

Electrochemical properties of LiFePO 4 thin films prepared by pulsed laser deposition

Lithium iron phosphate (LiFePO 4) thin film electrodes were prepared by pulsed laser deposition (PLD). The thin films were annealed at various temperatures under argon gas flow and the influence of annealing temperature on their electrochemical performance was studied. The thin films annealed at 773 and 873 K exhibited a couple of redox peaks at 3.4 V (versus Li/Li +) that are characteristics of the electrochemical lithium insertion/extraction of LiFePO 4. Atomic force microscopy (AFM) observation revealed that the film annealed at 773 K ( 773 K-film ) consisted of small grains with 50 nm in thickness, and the grain size increased with an increase of annealing temperature. Because of its small-sized grains, the 773 K-film showed high rate capability and the discharge capacity at 10 μA maintained 65% of that at 25 nA. However, the discharge capacity of the 773 K-film was ca. 10% smaller than that of the film annealed at 873 K, indicating that annealing at 773 K is slightly insufficient to obtain well-crystallized LiFePO 4. From these results, it was concluded that a point of optimization between high rate capability and capacity would be found between 773 and 873 K.

Physical and electrochemical properties of LiFePO 4/carbon composite synthesized at various pyrolysis periods

Aluminum-doped lithium iron phosphate was synthesized with a modified sol–gel process. The sol–gel derived cathodes show much higher conductivity than those prepared by a solid-state method. The conductivity is 8 × 10 −2 S cm −1 for the Al-doped LiFePO 4/carbon composite powders synthesized at 850 °C for 2 h, as determined using AC impedance spectroscopy. The electrodes consisting of the Al-doped LiFePO 4/carbon composite powders were fabricated for the electrochemical characterization and showed a specific capacity of about 150 mAh g −1 at C/40 rate. Not only the conductivity of the crystal lattice but also the conductivity of the grain boundary is enhanced for the nano-sized Al-doped LiFePO 4/carbon composite powders.

Electrochemical Properties of LiFePO<sub>4</sub> Cathode Thin Film Fabricated by Pulsed Laser Deposition

Electrochemical Properties of LiFePO<sub>4</sub> Cathode Thin Film Fabricated by Pulsed Laser Deposition

Pulsed Laser Deposition and Electrochemical Properties of LiFePO[sub 4] Thin Films

Well-crystallized and homogeneous LiFePO 4 films, of the order of 300 nm thick, have been grown by pulsed laser deposition on Pt-capped Si substrates in a one-step process. Their intrinsic lithium insertion properties have been evaluated both in aqueous and nonaqueous electrolytes. The films show the electrochemical fingerprint characteristic of pure triphylite LiFePO 4 , with, namely, equilibrium voltage at 3.42 V vs. Li + /Li. While carbon-free, the kinetic of the insertion/deinsertion process in such films compared favorably with those of optimized carbon-coated LiFePO 4 powders. Furthermore, we demonstrate sensor responses of these thin-film LiFePO 4 electrodes toward the quantitative detection of Li + ions in aqueous solutions as long as their concentration ranges from 10 - 4 to I M.