Preparación y caracterización de precursores mesoporosos de LiFePO4

II Encuentro sobre nanociencia y nanotecnología de investigadores y tecnólogos de la Universidad de Córdoba. NANOUC

Characterization of LiMxFe1–xPO4 (M = Mg, Zr, Ti) Cathode Materials Prepared by the Sol-Gel Method

A series of LiMxFe12xPO4 (M 5 Mg,Zr,Ti) phosphates were synthesized via a sol-gel method. Transmission electron microscopy observations show that LiMxFe12xPO4 particles consist of nanosize crystals, ranging from 40 to 150 nm. High-resolution TEM analysis reveals that a layer of amorphous carbon was coated on the surface of the LiMxFe12xPO4 particles, which substantially increases the electronic conductivity of LiMxFe12xPO4 electrodes. The doped LiMxFe12xPO4 powders are phase pure. Near full capacity ~170 mAh/g! was achieved at the C/8 rate at room temperature for LiMxFe12xPO4 electrodes. The doped LiMxFe12xPO4 electrodes demonstrated better electrochemical performance than that of undoped LiFePO4 at high rate

Thermodynamic Properties of Block Copolymer Electrolytes Containing Imidazolium and Lithium Salts

We report on the thermal properties, phase behavior, and thermodynamics of a series of polystyrene-block-poly(ethylene oxide) copolymers (SEO) mixed with the ionic species Li[N(SO_(2)CF_3)_2] (LiTFSI), imidazolium TFSI (ImTFSI), and an equimolar mixture of LiTFSI and ImTFSI (Mix). Differential scanning calorimetric scans reveal similar thermal behavior of SEO/LiTFSI and SEO/ImTFSI at the same salt concentrations. Phase behavior and thermodynamics were determined using a combination of small-angle X-ray scattering and birefringence. The thermodynamics of our mixtures can be mapped on to the theory of neat block copolymer phase behavior provided the Flory−Huggins interaction parameter, χ, between the blocks is replaced by an effective χ (χ_(eff)) that increases linearly with salt concentration. The phase behavior and the value of m, the slope of the χ_(eff) versus salt concentration data, were similar for SEO/LiTFSI, SEO/ImTFSI, and SEO/Mix blends. The theory developed by Wang [ J. Phys. Chem. B. 2008, 41, 16205] provides a basis for understanding the fundamental underpinnings of the measured value of m. We compare our experimental results with the predictions of this theory with no adjustable parameters

Graphene-analogues boron nitride nanosheets confining ionic liquids: a high-performance quasi-liquid solid electrolyte

Solid electrolytes are one of the most promising electrolyte systems for safe lithium batteries, but the low ionic conductivity of these electrolytes seriously hinders the development of efficient lithium batteries. Here, a novel class of graphene-analogues boron nitride (g-BN) nanosheets confining an ultrahigh concentration of ionic liquids (ILs) in an interlayer and out-of-layer chamber to give rise to a quasi-liquid solid electrolyte (QLSE) is reported. The electron-insulated g-BN nanosheet host with a large specific surface area can confine ILs as much as 10 times of the host's weight to afford high ionic conductivity (3.85 × 10−3 S cm−1 at 25 °C, even 2.32 × 10−4 S cm−1 at −20 °C), which is close to that of the corresponding bulk IL electrolytes. The high ionic conductivity of QLSE is attributed to the enormous absorption for ILs and the confining effect of g-BN to form the ordered lithium ion transport channels in an interlayer and out-of-layer of g-BN. Furthermore, the electrolyte displays outstanding electrochemical properties and battery performance. In principle, this work enables a wider tunability, further opening up a new field for the fabrication of the next-generation QLSE based on layered nanomaterials in energy conversion devices

Reaction Kinetic Analysis of Syntesized Lifepo4 Using Kissinger Method

The reaction kinetic analyses of synthesized LiFePO4 have been done using Kissinger method. LiFePO4 was prepared by mixing equimolar amount of LiCl, FeCl2.4H2O and H3PO4 in distilled water solution. Solution homogenization was achived by magnetic stirring and heating at 60 ºC. LiFePO4 precursor obtained after heat treatment at 200 ºC for 2 hours. LiFePO4 precursor was then analysized by using Differential Thermal Analysis (DTA) at heating rate of 5, 10, 15 and 20 ºC min-1 respectively. LiFePO4 powder was obtained after heating at 700 ºC for 4 hours, then the X-Ray Diffactometer (XRD) analysis was done to confirm phase purity and crystalline structure, meanwhile morphology observation was done by using Scanning Electron Microscope (SEM). By using Kissinger method, activation energy of LiFePO4 formation reaction was about Ea = 412 kJmol-1, and the frequeny factor A =1,1705 x 103

A detailed study of the lithiation of iron phosphate as well as the development of a novel synthesis of lithium iron silicate as cathode material for lithium-ion batteries

Dans cette thèse nous démontrons le travail fait sur deux matériaux de cathodes pour les piles lithium-ion. Dans la première partie, nous avons préparé du phosphate de fer lithié (LiFePO4) par deux méthodes de lithiation présentées dans la littérature qui utilisent du phosphate de fer (FePO4) amorphe comme précurseur. Pour les deux méthodes, le produit obtenu à chaque étape de la synthèse a été analysé par la spectroscopie Mössbauer ainsi que par diffraction des rayons X (DRX) pour mieux comprendre le mécanisme de la réaction. Les résultats de ces analyses ont été publiés dans Journal of Power Sources. Le deuxième matériau de cathode qui a été étudié est le silicate de fer lithié (Li2FeSiO4). Une nouvelle méthode de synthèse a été développée pour obtenir le silicate de fer lithié en utilisant des produits chimiques peu couteux ainsi que de l’équipement de laboratoire de base. Le matériau a été obtenu par une synthèse à l’état solide. Les performances électrochimiques ont été obtenues après une étape de broyage et un dépôt d’une couche de carbone. Un essai a été fait pour synthétiser une version substituée du silicate de fer lithié dans le but d’augmenter les performances électrochimiques de ce matériau.In this thesis, we demonstrate work on two different cathode materials for lithium-ion batteries. First, the synthesis of lithium iron phosphate (LiFePO4) is reproduced from literature using two lithiation methods starting with amorphous iron phosphate (FePO4). For both reactions, the product at each step of the synthesis was analyzed using Mössbauer Spectroscopy and X-ray diffraction in order to gain further insight of the reaction mechanism. The results of this work were published in Journal of Power Sources. The second cathode material of interest was lithium iron silicate (Li2FeSiO4). A novel synthetic method was developed to produce lithium iron silicate cost effectively starting with low cost precursors and basic laboratory equipment. The material was synthesized using a solid- state synthesis after milling and carbon coating, electrochemical performance was evaluated. An attempt was made to synthesize off-stoichiometric lithium iron silicate in order to increase the electrochemical performance of the material

Composite Electrolytes for Lithium Batteries: Ionic Liquids in APTES Crosslinked Polymers

Solvent free polymer electrolytes were made consisting of Li(+) and pyrrolidinium salts of trifluoromethanesulfonimide added to a series of hyperbranched poly(ethylene oxide)s (PEO). The polymers were connected by triazine linkages and crosslinked by a sol-gel process to provide mechanical strength. The connecting PEO groups were varied to help understand the effects of polymer structure on electrolyte conductivity in the presence of ionic liquids. Polymers were also made that contain poly(dimethylsiloxane) groups, which provide increased flexibility without interacting with lithium ions. When large amounts of ionic liquid are added, there is little dependence of conductivity on the polymer structure. However, when smaller amounts of ionic liquid are added, the inherent conductivity of the polymer becomes a factor. These electrolytes are more conductive than those made with high molecular weight PEO imbibed with ionic liquids at ambient temperatures, due to the amorphous nature of the polymer

Production of carbon nanotubes over Fe-FSM-16 catalytic material: effect of acetylene flow rate and CVD temperature

In this article, a high-yield synthesis of high-quality CNTs using Fe catalysts trapped within channels of Folded Sheet Mesoporous Materials, FSM-16 by Chemical Vapor Deposition CVD using acetylene as a hydrocarbon source is reported. The effect of reaction temperature and acetylene flow rate on the formation of CNTs was investigated. It was found that the yield, diameter and quality of CNTs synthesized strongly depend on reaction temperature during CVD. The resulting materials were characterized by scanning electron microscopy (SEM), Raman spectroscopy, and thermogravimetric analysis (TGA). Our research found that carbon deposition, diameter and quality of the CNTs strongly depend on CVD temperature. However acetylene flow rate did not have any significant effect on diameter distribution. Raman measurement indicated that the synthesized products were MWCNTs. High-resolution transmission electron micrographs of samples reveal the multilayer sidewalls of individual MWCNTs with a diameter of 40 nm, in which hollow and tubal structures were observed