LiFePO4 Powders Research Articles

Enhanced Electrochemical Properties of LiFePO<sub>4</sub> as Positive Electrode of Li-Ion Batteries for HEV Application

LiFePO4 materials synthesized using FePO4(H2O)2 and Li2CO3 blend were optimized in view of their use as positive electrodes in Li-ion batteries for hybrid electric vehicles. A strict control of the structural properties was made by the combination of X-ray diffraction, FT-infrared spectroscopy and magnetometry. The impact of the ferromagnetic clus-ters (γ-Fe2O3 or Fe2P) on the electrochemical response was examined. The electrochemical performances of the opti-mized LiFePO4 powders investigated at 60℃ are excellent in terms of capacity retention (153 mAh·g-1 at 2C) as well as in terms of cycling life. No iron dissolution was observed after 200 charge-discharge cycles at 60℃ for cells containing Li foil, Li4Ti5O12, or graphite as negative electrodes.

Hydrothermally synthesized LiFePO4 crystals with enhanced electrochemical properties: simultaneous suppression of crystal growth along [010] and antisite defect formation

Improving electrochemical properties of hydrothermally synthesized LiFePO(4) powders is of immense technological significance and has been a subject of much scientific inquiry for many years. As reported previously, reversing the feeding sequence of starting materials and/or introducing ethylene glycol (EG) could significantly improve the electrochemical performance of hydrothermally synthesized LiFePO(4). However, the mechanism remains unclear. Here, we report a systematic study to understand the mechanism from viewpoints of crystal growth and defect concentration control. Combining the results of experimental and theoretical investigations, the improvement in electrochemical performance is attributed to simultaneous suppression of crystal growth along the [010] direction and reduced defect concentration of the antisite. The reduction in antisite defects is readily monitored by significant red shift of the infrared (IR) absorption band around 1000 cm(-1) which is assigned to the symmetric stretching P-O vibration of the PO(4) tetrahedron, as indicated by theoretical calculation. With this knowledge in mind, an output as high as 450 g L(-1) (autoclave volume), and an enhanced specific discharge capacity of 165 A h kg(-1) (close to the theoretical unity of 170 A h kg(-1)) at 0.1 C are achieved.

Rapid crystallization of LiFePO4 particles by facile emulsion-mediated solvothermal synthesis

Lithium iron phosphate powders were obtained by solvothermal treatments of quaternary emulsions Triton X-100/cyclohexane/n-hexanol/water at low temperature (180°C), with or without stirring. Such synthesis conditions allowed for fast crystallization of pure olivine-type LiFePO4 powder, evidenced by the X-ray powder diffraction measurements and energy dispersive spectroscopy. It has been found that stirring drastically changes the morphology of LiFePO4 particles, causing a preferential crystal orientation. Also, a great difference in the morphology was demonstrated by field emission scanning electron microscopy. The powder obtained after only half an hour of the dynamic solvothermal treatment, without additional post annealing, and without carbon coating, was electrochemically active, showing the discharge capacity of 115mAhg−1.

Nanostructured high specific capacity C-LiFePO4 cathode material for lithium-ion batteries

Abstract

ChemInform Abstract: Fabrication and Electrochemical Characteristics of LiFePO4 Powders for Lithium‐Ion Batteries

AbstractReview: 154 refs.

Electrochemical properties of Nano-LiFePO4 prepared by hydrothermal reaction

LiFePO4 nanorods were facilely synthesized under hydrothermal condition. The crystalline structure and particle morphology of LiFePO4 powders were characterized by X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). The electrochemical properties of LiFePO4/Li cells were investigated by galvanostatic test and cyclic voltammetry (CV). The XRD result demonstrated LiFePO4 powder had an orthorhombic structure with a space group of Pnma. The synthesized LiFePO4 nanorods exhibited a first discharge capacity of 155 mAh·g−1 (91% of theorectical capacity) close to the theorectical capacity of LiFePO4 (170 mAh · g−1) at 0.1 C.

A Simple and Facile Preparation of LiFePO4 by a One-step Microwave Hydrothermal Method

A novel method was used to synthesize LiFePO4, using inorganic salts as raw materials, and PEG-4000 as the surfactant. The results show that LiFePO4 powders with various morphologies were prepared by microwave hydrothermal method, and it is very important to synthesize the LiFePO4 powders with well-defined shape and size controlling experimental conditions, such as the solution pH and surfactant. The modified preparation of LiFePO4 was built. The coating carbon on LiFePO4 powders as a core–shell structure was carried out by annealing in 3%H2/97%N2 at 700 °C for 2 h. As a result, the diffusion coefficient of lithium ions can be increased, and the reversibility of lithium intercalation and deintercalation can be improved markedly. In addition, LiMn0.08Fe0.92PO4 powders were synthesized, which were observed in an ordered olivine structure, but great changes occurred in morphology. Doping Mn2+ does not destroy the lattice structure and enlarges the lattice volume. Consequently, the conductivity can be enhanced, and the lithium ion diffusion coefficient can be boosted. Initial discharge capacity is improved obviously, and increases to 99.6 mA h g−1 and 93.8 mA h g−1 respectively. The microwave assisted hydrothermal approach presented here opens a potential avenue to explore the synthesis of LiFePO4 powders.

Effect of slurry preparation and dispersion on electrochemical performances of LiFePO4 composite electrode

A study is attempted on how the dispersion of solid ingredients in solvent affects the electrochemical performance of LiFePO4 composite electrode. The slurries comprising LiFePO4 powder, carbon black and polymeric binder in solvent NMP (N-methyl-2-pyrrolidone) are prepared by two different processes, and results in different dispersion qualities. With better dispersion, the surfactant (Triton-100) is added into slurry as dispersing agent, whereas no dispersing agent in the other sample. The former process leads to more uniform dispersion of solid ingredients as compared to the latter. In the composite electrode prepared from the former process, the LiFePO4 and carbon black particles are homogeneously distributed without obviously reunion. Indebted to this favourable feature, this electrode exhibits a better high C-rate electrochemical performance for cycling and capacity than those without the surfactant.

Electrochemically assisted growth of LiFePO4 in ionic liquid media

Electrodeposition techniques in aqueous media have so far been widely used in the field of battery research to make either nano-architectured current collectors or electrode materials. Deviating from such an approach we have explored ionic liquid media as electrolytic bath. Here we report the electrochemically-assisted synthesis of LiFePO4 in the 1-ethyl-3-methylimidazolium bis(TriFluoromethaneSulfonyl)imide ([EMIm]TFSI) ionic liquid medium. Electrochemically active LiFePO4 powders with particles size of 500nm were obtained from the electrolytic ionic liquid bath containing FeCl3 and Li3PO4 by conducting chronoamperometry at 275°C. Moreover, LiFePO4 thick deposits have also been successfully prepared on a Li3PO4-loaded substrate.

Synthesis of the LiFePO4 by a solid-state reaction using organic acids as a reducing agent

Olivine LiFePO4 using organic acid as a reducing agent has been synthesized utilizing a solid-state method. Samples were characterized by an X-ray diffraction and a scanning electron microscope. The single-phase LiFePO4 and small grain size of the crystallite were obtained without the use of a carbon-coating process. In such LiFePO4 powder, the initial specific capacity was 142 mAhg−1 at a current rate of 0.1 C. After the 50th cycle test, the reversible specific capacity was 132 mAhg−1 at a 2 C rate, showing a retention ratio to the initial capacity as 98.4%.

Synthesis of LiFePO<sub>4</sub> Cathode Materials by a Chemical Method

The olivine-type LiFePO4 powder was prepared by a chemical method using the synthesized FePO4⋅2H2O, LiOH and glucose as raw materials. The synthesized FePO4⋅2H2O powder was obtained by co-precipitation method. FePO4⋅2H2O and LiFePO4 powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed the synthesized FePO4⋅2H2O powder at pH of 2.05 was in a single phase and nearly spherical in shape. Using the synthesized powders to prepared LiFePO4 at 600 °C in vacuum for 2 h was nearly spherical in shape and whose size was in the range of 0.1-0.5μm.

Structure and Electrochemical Characteristics of LiFePO4 as Cathode Material for Lithium-Ion Batteries

To prepare cathode material for lithium batteries, LiFePO4 powder was sputtered using an RF magnetron. Thin LiFePO4 films were obtained on different ~1000 nm thick substrates. The compositional and morphological examination of these films by SEM has shown that on a silicon substrate the annealed nano-crystalline thin film of LiFePO4 material condenses in larger monocrystals (with thin film disappearance), while such a film on the stainless steel substrate coalesces in a uniform nano-structured layer after annealing. As shown by the energy-dispersive X-ray analysis, the annealed film consists of phosphorus, iron, and oxygen in the ratio corresponding to the stoichiometric LiFePO4. Cyclic voltammograms of the LiFePO4 thin layer were obtained with typical red-ox reaction peaks characterizing the electrochemical lithium insertion/extraction reactions in LiFePO4. The obtained thin films have a relatively high charge capacity of 127 mAh g-1.

Al Current Collectors for Li-Ion Batteries Made via an Oxidation Process in Ionic Liquids

Efficient electrical wiring of electrodes is a key issue in the design of Li-ion batteries using insulating compounds. Approaches acting at the material level are being pursued by combining techniques to decrease the particles size and to coat them with carbon. Here, we report the texturation of the Al current collector as an additional mean to improve electrode kinetics. Bulk aluminum substrates were oxidized from EMIm TFSI/AlCl3 electrolytic baths using cyclic voltammetry techniques. A needlelike morphology was obtained after oxidation. Electrodes using this substrate and LiFePO4 powders as the active material were shown to display excellent capacity retention and high rate capability. © 2010 The Electrochemical Society. DOI: 10.1149/1.3511717 All rights reserved.

Synthesis and electrochemical properties of LiFePO4/C composite cathode material prepared by a new route using supercritical carbon dioxide as a solvent

From the viewpoint of energy efficiency and cost, an intensive search for less energy demanding synthesis methods for LiFePO4 appears quite attractive and is still in full swing. Here, we report that carbon coated LiFePO4 (LiFePO4/C) powders can be successfully synthesized by a new route using supercritical carbon dioxide as a solvent. The obtained high-purity LiFePO4/C powders are uniform in shape and 0.5 µm to 1 µm in size. As for the electrochemical performance, at the current density of 0.1 C, the electrode exhibits a discharge capacity of 158 mA h g−1 as well as good cycling stability—there is no obvious capacity fading after 100 cycles. When the synthesis reaction temperature increases from 50 to 200 °C, the primary particle size grows from approximately 0.5 to 2 µm, and the initial discharge capacity decreases from 158 to 41 mA h g−1, which shows that 50 °C is the optimum temperature to synthesize LiFePO4 in supercritical carbon dioxide. Needless to say, such a new approach, which is not specific to LiFePO4, offers great opportunities for the synthesis of new electrode materials.

Effect of Carbon Sources on the Battery Properties of LiFePO4/C Cathode Materials Prepared by Spray Pyrolysis

LiFePO4/C cathode materials were prepared by spray pyrolysis, and the effect of carbon source and calcination condition on powder characteristics and battery properties of the materials were studied. Homogeneous olivine LiFePO4 powders were formed from all carbon sources, and carbon contents of LiFePO4/C particles prepared from fructose or sucrose were high due to their high pyrolysis temperature. Particle morphology was changed according to carbon source, and crystal growth was promoted by increasing calcination temperature. Carbon layers were observed on the surface of LiFePO4/C particles. Battery properties were improved by increasing carbon content of LiFePO4/C particles, but the properties also depended largely on their particle size. So it revealed that the discharged capacity of LiFePO4/C cathode was maximized when both their carbon content and particle size showed optimum value. The discharged capacity of LiFePO4/C cathode prepared from sucrose exhibited 153 mAh/g at 1 C when it was calcined at 750°C for 3 hr.

Influence of Carbon Nanotubes on the Performances of LiFePO<sub>4</sub>

To improve the performances of LiFePO4, a positive material in lithium battery, research on the influence of doping amount and doping form of carbon nanotubes (CNTS) on electrical resistivity, specific capacity, specific surface area and particle size distribution of LiFePO4 powder was conducted. The results indicated that, addition of CNTS significantly reduced the electrical resistivity no matter in pure LiFePO4 or LiFe0.98Mg0.02PO4; with same usage, coating of CNTS as carbon source performed better than mechanical grinding and mixing with LiFePO4. With the increase of CNTS content, a rising trend of both specific surface area (BET) and particle size (D50) in LiFePO4 powder was observed, but seeing a slight drop in discharge capacity under the rates of 0.2C and 0.5C. When the content of CNTS reached 3% (by mass) respectively through mechanical mixing and being added as carbon source, electrical resistivity of pure LiFePO4 dropped from over 105Ω•cm to 1868Ω•cm and 27Ω•cm accordingly, and that of LiFe0.98Mg0.02PO4 dropped from over 105Ω•cm to 4800Ω•cm.

Studies on Preparation and Properties of LiFePO<sub>4</sub> Cathode Material Modified by Polyacenic Semiconductor Materials for Lithium Ion Batteries

The composite materials of LiFePO4 powder coated with polyacenic semiconductor materials (PAS) were successful prepared. Effects of the preparation conditions, such as precursor material, annealing temperature et al., on the structure and electrochemical properties of LiFePO4 were studied. SEM images and TG thermogravimetric analysis of the obtained carbon coating microspheres suggest that LiFePO4 powder was successfully encased within the carbon gel microspheres. The electrical conductivity of the composite materials could get to 10-2 S•cm-1. It was found that the composite LiFePO4 material exhibits excellent capability with initial discharge capacity more than 210 mAhg–1. The discharge capacity goes up to 340 mAh/g after ten times of cycle.

Improvement of the Electrochemical Properties in Nano-Sized Al<sub>2</sub>O<sub>3</sub> and AlF<sub>3</sub>-Coated LiFePO<sub>4</sub> Cathode Materials

The surface conditions of LiFePO4 powder were modified by adding AlF3 and Al2O3 by using the sol-gel process to improve its electrochemical properties. The surface of LiFePO4 powders was partially covered with nano-sized AlF3 and Al2O3, which is confirmed by using a transmission electron microscope image. The states of coated Al materials were examined by using X-ray photoelectron spectrometer results. The nano-sized AlF3- and Al2O3-coated LiFePO4 powders showed no difference in the bulk structure compared with the pristine one. However, the AlF3- and Al2O3-coating on LiFePO4 powders improved the overall electrochemical properties such as the discharge capacity, the cyclability, and the rate capability compared with those of a pure LiFePO4. Such enhancements were attributed to the presence of a stable AlF3 and Al2O3 layer which acts as an interfacial stabilizer on the surface of LiFePO4 powders.

Evaluation of Surface Acid and Base Properties of LiFePO4in Aqueous Medium with pH and Its Electrochemical Properties

Changes in the surface chemistry of LiFePO4 cathodes in an aqueous medium for lithium ion battery are investigated based on a quantitative evaluation of surface functional groups of LiFePO4 as a function of pH. It is found that, while the dissolution of Li ions from LiFePO4 increases the number of acidic surface groups, the dissolution of Fe ions reduces the number of basic surface groups. The pKa values for various processing conditions are calculated. Interestingly, none of the investigated processing conditions changes the characteristic acid moieties on the particles (pKa ∼ 2.8). However, the processing condition strongly impacts the chemistry of the basic surface groups showing three distinct basic surface groups with pKb values of 0.1, 0.9, and 1.5, respectively. Correlation is made between dissolution behavior, surface groups, dispersion properties, and electrochemical properties. It is found that Li-and Fe-ion depleted LiFePO4 powder increases the viscosity in N-methylpyrrolidone pastes 5-fold and...

Fabrication and Electrochemical Characteristics of LiFePO<sub>4</sub> Powders for Lithium-Ion Batteries

Novel powder fabrication technologies provide opportunities to develop high-performance, low-cost cathode materials for rechargeable lithium-ion batteries. Among various energy storage technologies, rechargeable lithium-ion batteries have been considered as effective solution to the increasing need for high-energy density electrochemical power sources. Rechargeable lithium-ion batteries offer energy densities 2–3 times and power densities 5–6 times higher than conventional Ni-Cd and Ni-MH batteries, and as a result, they weigh less and take less space for a given energy delivery. However, the use of lithium-ion batteries in many large applications such as electric vehicles and storage devices for future power grids is hindered by the poor thermal stability, relatively high toxicity, and high cost of lithium cobalt oxide (LiCoO2) powders, which are currently used as the cathode material in commercial lithium-ion batteries. Recently, lithium iron phosphate (LiFePO4) powders have become a favorable cathode material for lithium-ion batteries because of their low cost, high discharge potential (around 3.4 V versus Li/Li+), large specific capacity (170 mAh/g), good thermal stability, and high abundance with the environmentally benign and safe nature. As a result, there is a huge demand for the production of high-performance LiFePO4 powders. However, LiFePO4 also has its own limitation such as low conductivity (∼10−9 S/cm), which results in poor rate capability. This can be addressed by modifying the powder structure using novel fabrication technologies. This paper presents an overview of recent advances in the fabrication of high-performance LiFePO4 powders for lithium-ion batteries. The LiFePO4 powder fabrication methods covered include: solid-state synthesis, mechanochemical activation, carbothermal reduction, microwave heating, hydrothermal synthesis, sol-gel synthesis, spray pyrolysis, co-precipitation, microemulsion drying, and others. The impacts of these fabrication methods on the structure and performance of LiFePO4 powders are discussed. In addition, the improvement of the conductivity of LiFePO4 powders through novel powder technologies is addressed.