Bimodal mesoporous titanium dioxide anatase films templated by a block polymer and an ionic liquid: influence of the porosity on the permeability

In the present paper, we report the synthesis of bimodal mesoporous anatase TiO2 films by the EISA (Evaporation-Induced Self-Assembly) method using sol-gel chemistry combining two porogen agents, a low molecular weight ionic template and a neutral block copolymer. The surfactant template (C(16)mimCl) generates non-oriented worm-like pores (8 to 10 nm) which connect the regularly packed ellipsoidal mesopores (15 to 20 nm diameter) formed by an amphiphilic block copolymer of the type poly(isobutylene)-b-poly(ethylene oxide) (PIB-PEO). The surfactant template can also significantly influence the size and packing of the ellipsoidal mesopores. The mesostructural organization and mesoporosity of the films are studied by Environmental Ellipsometry-Porosimetry (EEP), Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) and electron microscopy techniques. Electrochemical characterization is performed to study the permeability of the films to liquid solutions, using two types of probe moieties (K3FeIII(CN)(6) and Ru(bpy)(3)(2+)) by the wall-jet technique. An optimum ratio of C(16)mimCl/PIB-PEO provides anatase films with a continuous bimodal mesopore structure, possessing a permeability up to two times higher than that of the mesoporous films templated by PIB-PEO only (with partially isolated mesopores). When C(16)mimCl is used in large quantities, up to 20% weight vs. PIB-PEO, large overall porous volume and surface area are obtained, but the mesostructure is increasingly disrupted, leading to a severe loss of permeability of the bimodal films. A dye-sensitized solar cell set-up is used with anatase films as the photoelectrode. The photosensitizer loading and the total energy conversion efficiency of the solar cells using the mesoporous films templated by an optimal ratio of the two porogen agents C(16)mimCl and PIB-PEO can be substantially increased in comparison with the solar cells using mesoporous films templated by PIB-PEO only.DFG/SM 199/6-1DFG/OE 420/5-1BMBF/SOHyb/03X3525

Etudes électrochimiques de cinétiques de polycondensation sol-gel et de la fractalité des xérogels

6-triethoxysilane-1-hexyl-ferrocene is stable, able to connect irreversibly with growing polysiloxanes, and has electrochemical properties ; all of this allows using this molecule as a redox probe. Electrochemical studies (cyclic voltammetry, chronoamperometry) confirm the influence of nature of the catalyst in the diffusion coefficients evolution of growing polysiloxanes (gel time and structures of polymers in solution). First results with modified electrodes seem like to link the nature of the catalyst to the last structure of silica xerogels (fractal, isotropic) and their electrochemical properties. For ormosils matrix hybrid sol-gels and titanium/phosphonate hybrid sol-gels, the use of well redox probes allow us to study the evolution of such complex system and show the influence of each of the parameters when this materials are formed.Le 6-triéthoxysilyl-1-hexyl-ferrocène est une molécule stable, pouvant se lier de manière irréversible aux polysiloxanes en croissance, et possédant des propriétés électrochimiques, pour pouvoir l'utiliser comme une nouvelle sonde rédox. Les études électrochimiques (voltammétrie cyclique, chronoampérométrie) confirment l'influence du type de catalyseur dans l'évolution des coefficients de diffusions des polysiloxanes en croissance (détermination du temps de gel et des structures des polymères en solutions). Les résultats préliminaires sur des électrodes modifiées semblent lier la nature du catalyseur à l'organisation des xérogels de silice (fractals, isotrope) et leurs propriétés électrochimiques. Pour les sols-gels hybrides à matrice ormosils et les sol-gels de titane/phosphonate, l'utilisation de sondes rédox appropriées permet de suivre l'évolution de ces systèmes complexes et montrent l'influence des différents paramètres lors de la formation de ces matériaux

Improved electrochemical performances of Li-rich nickel cobalt manganese oxide by partial substitution of Li+ by Mg2+

International audienceLi-rich nickel cobalt manganese oxide (NCM) materials with partial substitution of lithium by magnesium is synthesized by the Pechini process. Different synthesized Li100-2xMgx-NCM materials (x = 0, 1, 2.5, 5, and 10) are investigated by X-ray diffraction (XRD), neutron diffraction, and scanning electron microscopy to determine the role of Mg in the structure and its impact on the morphology and electrochemical properties. The chemical composition, crystal structure, and particle morphology are compared with those of the reference (x = 0) material. Mg substitution has a significant impact on the electrochemical properties. In comparison with the reference sample, the x = 1 sample exhibits a mitigation of the voltage drop owing to more stable structure during cycling, leading to a specific discharge of 210 mAh g−1 after 100 cycles at C/10 rate. However, compositions with x ≥ 2.5 exhibit larger voltage drop in discharge, due to the faster formation of a spinel-like structure during cycling

Cr-Doped Li-Rich Nickel Cobalt Manganese Oxide as a Positive Electrode Material in Li-Ion Batteries to Enhance Cycling Stability

International audienceLi-rich nickel cobalt manganese oxide materials with Cr doping were designed in order to improve the cycling stability of Li-rich cathode materials. Several samples with the chemical formula Li1.171(Ni0.191Co0.099Mn0.539)O2, Li1.148Cr0.008(Ni0.191Co0.099Mn0.539)O2, Li1.112Cr0.019(Ni0.191Co0.099Mn0.539)O2, and Li1.171Cr0.039(Ni0.191Co0.099Mn0.539)O2 labeled, respectively, HE-NCM, Li100–3xCrx-NCM (x = 0.67 and 1.67), and Li100Cr3.33-NCM were synthesized by the Pechini method. The materials were characterized by X-ray and neutron diffraction as well as with scanning electron microscopy (SEM). The Li100Cr3.33-NCM material displays the best mitigation of the potential drop after 100 cycles. After 100 cycles, Li98Cr0.67-NCM, Li95Cr3.33-NCM, and Li100Cr3.33-NCM deliver a stable specific charge higher than 200 mA h/g with high-loaded electrodes. While the Li100–3xCrx-NCM samples still display a significant fading of their average discharge potential, the average discharge potential of Li100Cr3.33-NCM material is better stabilized at a value offering a specific energy superior to 700 W h/kg, thus confirming the advantages of Cr doping

Fe and Co methylene diphosphonates as conversion materials for Li-ion batteries

International audienceOrganic-inorganic hybrid materials can introduce more flexibility in the choice of Li-ion battery materials due to the versatility of organic ligands. As an alternative to carboxylate-based ligands, Fe and Co methylene diphosphonate were successfully synthesised and tested as model diphosphonate-based negative electrode materials for Li-ion batteries, showing specific charges of 250 mAh g−1 and 395 mAh g−1 after 100 cycles at 50 mAh g−1, respectively. Operando X-ray diffraction and ex situ X-ray absorption spectroscopy confirmed the expected conversion reaction mechanism involving amorphisation of the pristine materials and extrusion of transition metal particles upon reduction. Ex situ X-ray absorption spectra indicated that Fe methylene diphosphonate undergoes reversible Fe cycling between Fe(II) and Fe(0) metal particles

Electrogenerated chemiluminescence in an electrodeposited redox hydrogel

We report the electrodeposition, under physiological conditions, of an electrochemiluminescent (ECL)Ru2+/3+ complex-containing redox hydrogel. The ECl-hydrogels were formed by potential cycling of a solution of [poly(4-vinylpyridine)Ru(2,2' -bypyridine)2CL-]+/2+, its un-coordinated backbone pyridines partially quaternized with bromoethylamine for solubility in water and for swelling to a hydrogel after crosslinking. The polymer was electrosorbed on plasma-oxidized graphite in the cathodic half cycle. The ECL resulted of the chemical reaction of electro-oxidatively produced tri-n-propylamine-radical with the hydrogel's Ru2+ centers. The emission spectra of the photo-excited films and their ECL spectra were identical. The ECL-emission increased one thousand-fold, linearly with the tri-n-propylamine (TPrA) concentration, between 100nM and 0.1 mM

Multiple redox couples cathode material for Li-ion battery: Lithium chromium phosphate

International audienceCarbon coated Li3Cr2(PO4)3/C model materials were synthesized by a sol-gel route and a solid state route with calcination at 800 °C under an inert atmosphere. The model materials were characterized by X-ray diffraction (XRD), neutron powder diffraction (NPD), scanning electron microscopy (SEM), laser diffraction analysis (granulometry) and thermogravimetric analysis (TGA). The electrochemical signatures obtained for the solid state (carbon coated) route synthesized compounds revealed the presence of two redox couples, Cr3+/Cr2+ and Cr4+/Cr3+, between 1.5–2.5 V and 4.0‐4.9 V vs. Li+/Li, respectively. The model materials show an initial specific charge (for lithiation) of 131 mAh g−1 (sol-gel, carbon coated) and 119 mAh g−1 (solid state, carbon coated), which decreases to 90 mAh g−1 and 46 mAh g−1, respectively, after 100 cycles. Operando XRD measurements revealed reversible structural changes in the crystal structure upon cycling, leading to the conclusion of an insertion reaction mechanism

A Cylindrical Cell for Operando Neutron Diffraction of Li-Ion Battery Electrode Materials

Neutron diffraction is a powerful technique to localize and quantify lithium in battery electrode materials. However, obtaining high-quality operando neutron diffraction data is challenging because it requires achieving good electrochemical performance while cycling a large amount of active material to ensure optimal signal-to-noise ratio. We have developed a cylindrical cell specifically suited for operando neutron diffraction studies, and used it to investigate the structural changes in the Ni-rich LiNi0.6Co0.2Mn0.2O2 cathode material during cycling between 2.5 and 4.3 V vs. Li+/Li. The cell demonstrates reliable electrochemical performance, even after long-term cycling, and the important crystal structure parameters of the active material, including Li occupancy, could be successfully refined with the Rietveld method using neutron diffraction data collected in operando after appropriate background subtraction

Lithium Iron Methylenediphosphonate: a Model Material for New Organic-Inorganic Hybrid Positive Electrode Materials for Li Ion Batteries.

To increase the energy density of lithium ion batteries, new electrode materials with superior performance are ceaselessly being searched for. To combine the advantages of organic and inorganic materials, the creation of organic–inorganic hybrid materials is a promising option for the future. In this work, we introduce hydrothermally synthesized lithium iron methylenediphosphonate (Li_1.4­Fe_6.8­[CH₂­(PO₃)₂]₃­[CH₂­(PO₃)­(PO₃H)]·4H₂O) as a model material for a new class of organic–inorganic hybrid materials for Li ion battery positive electrodes. Hereby, we validate the concept of using diphosphonate ligands for hybrid Li ion battery materials. Structure determination based on neutron and X-ray powder diffraction data indicates a monoclinic phase containing three different Fe positions, which is confirmed by Mössbauer spectroscopy. The material achieves a specific charge of 128 (mA h)/g upon galvanostatic cycling after 200 cycles at a theoretical value of 168 (mA h)/g. Operando X-ray absorption near-edge spectroscopy results confirm the reversible cycling of Fe ions between Fe­(II) and Fe­(III), and ex situ superconducting quantum interference device measurements indicate an exchange of 0.6 electron per Fe atom in the first cycle, in agreement with the specific charge obtained for the first reduction. This proves the applicability of transition-metal diphosphonates as positive electrode materials for Li ion batteries