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Na2Mn1.5Fe1.5(PO4)3 (NMFP) dandelion sphere-like particles were successfully synthesized via a hydrothermal route without addition of any templates or surfactants (laboratory and pilot scales). The hydrothermal reactor (pilot scale) is equipped with stirrer for continuous agitation of reagents during the reaction. The obtained materials were characterized by X-ray diffraction, Mossbauer spectroscopy and Scanning electron microscopy. Results show that Na2Mn1.5Fe1.5(PO4)3 samples obtained from the reaction performed at laboratory scale have hierarchical dandelion sphere-like morphology and the dandelions consist of micro-/nano-rods. On the other hand, we obtained the self-assembly nano-rods morphology for the particles prepared using hydrothermal reactor. On the basis of the experimental results, a growth mechanism of Na2Mn1.5Fe1.5(PO4)3 self-assembly and dandelion sphere-like particles was proposed. Temperature and time of hydrothermal reaction are found to be crucial parameters in controlling the growth of Na2Mn1.5Fe1.5(PO4)3 particles. In addition, investigation of the effect of continuous stirring during the hydrothermal reaction shows that the reaction time can be optimized to obtain Na2Mn1.5Fe1.5(PO4)3 with small particles size. The influence of stirring on the NMFP morphology has been clearly evidenced. Indeed, the stirring leads to homogeneous particles. Cycling studies have shown that the synthesized Na2Mn1.5Fe1.5(PO4)3 dandelions materials exhibit specific discharge capacities of about 62 and 57 mAh g− 1 equivalent to about 1.2 and 1.05 lithium ions de-intercalated at C/15 and C/10 current density respectively.

In this report, we successfully demonstrate a novel SiF 4 treatment on lithium manganese iron phosphate cathode (LMFP) that can significantly improve its hydrophobic property. The effect of SiF 4 treatment on the structure and hydrophobicity of LMFP powder was studied by X-ray diffraction, Fourier transform infra-red spectroscopy, scanning transmission electron microscopy–energy dispersive X-ray spectroscopy, Karl Fisher titration, and thermo-microbalance gravimetric studies. The SiF 4 treated LMFP cathode shows a substantial decrease in moisture adsorption by up to half of the untreated LMFP under ambient conditions. The SiF 4 -treated LMFP also shows excellent cycle life when cycled in lithium-ion full cells, even after exposing the electrodes to ambient conditions for one day, while the untreated LMFP showed a decrease in cycle life after the same exposure.

Three materials based on sodium iron phosphate with a Maricite structure were synthesized by hydrothermal method and solid-state synthesis. The materials have been characterized by X-ray diffraction, thermal analysis, and surface analysis. The materials were used for the fabrication of electrodes and their electrochemical performance were evaluated in lithium batteries. The material with the highest reversible capacity was then characterized in sodium batteries. Both the capacity exhibited at low discharge rate as well as the capacity as a function of the discharge rate and cycle number were evaluated. The obtained values were used for the determination of the specific energy as a function of the specific discharge power. At the lower discharge rate (C/20), the material was able to deliver 52.0 mAh g- 1 with an average charge voltage of 2.5 V corresponding to a specific energy of 130 Wh kg- 1. The specific capacity recorded at the lowest discharge rate gradually increased with the number of cycles and reached a value of 63 mAh g- 1 at the 150th cycle. © 2014 Elsevier B.V.

International audience; This paper describes the preparation, characterization and electrochemical study of various iron and lithium iron phosphates. The pristine iron phosphate samples obtained were amorphous materials with various textural properties, in terms of average pore size, pore order and specific surface area. Some solids were mesoporous, featuring high surface area, narrow pore size distribution and high pore volume. Lithium iron phosphates were obtained by chemical lithiation of these iron phosphates, using LiI dissolved in acetonitrile. These materials were amorphous and electrochemically inactive against lithium. Following heating at 550 °C, the materials crystallized and showed disparate electrochemical performance in lithium half-cells. This can be ascribed not only to the presence in the samples of impurities of different nature (and inherent to the synthesis method), but also to different textural and morphological properties. In fact, the best electrochemical performance was that of crystallized LiFePO4 obtained from the mesoporous iron phosphate and consisting of rounded nanoparticles with high surface area and adequate porosity. As a result, a better electrolyte impregnation in the porous structures is highly expected. Furthermore, enhancement of the lithium ion diffusion inside the network is observed. This justifies the potential use of carbon-free mesoporous precursors of LiFePO4. However, introduction of a conductive carbon coating onto the phosphate particles and/or removal of the impurities prove necessary for good capacity retention upon cycling.

International audience; A new iron phosphate, KMgFe(PO4)2 has been synthesized and investigated by X-ray diffraction, Mössbauer spectroscopy and ionic conductivity. This compound crystallizes in the monoclinic space group C2/c with the parameters a = 18.529(7) Å, b = 5.402(3) Å, c = 9.374(9) Å, β = 120.64(5)° and Z = 4. Its original structure can be described as the stacking along the [101] direction of [MgFe(PO4)−2]∞ layers of corner-sharing MO4 (M = 0.5 Fe + 0.5 Mg) and PO4 tetrahedra. The K+ ions are occupying the inter-layer space. The Mössbauer spectroscopy confirms the occurrence of only tetrahedral Fe3+ ions and gives a definitive proof of the disordered character of their distribution. Ionic conductivity results obtained by the impedance spectroscopy technique show that this material is a two-dimensional ionic conductor, with low activation energy, 0.51 eV, that is interpreted on the basis of two-dimensional pathways.

Well-crystallized Li3Fe2(PO4)3 with an orthorhombic β-Fe2(SO4)3-type structure was able to be synthesized by using two synthetic routes, where hydrothermal reaction and successive heat treatment with relatively low temperatures were employed. The samples prepared were found to show orthorhombic symmetry, contrary to the fact that a conventional solid state synthesis heating at temperatures higher than 1000 °C usually gives monoclinic symmetry. The sample showed two plateau potentials of 2.8 and 2.7 V vs. Li/Li+ upon discharge, and the total discharge capacity of the sample exhibited more than 80 mA h g−1 under 0.5 mA cm−2.