Eco-friendly synthesis of SiO2 nanoparticles confined in hard carbon: A promising material with unexpected mechanism for Li-ion batteries

Times Cited: 3Nita, Cristina Fullenwarth, Julien Monconduit, Laure Le Meins, Jean-Marc Fioux, Philippe Parmentier, Julien Ghimbeu, Camelia MateiGhimbeu, Camelia/N-7855-2015Ghimbeu, Camelia/0000-0003-3600-587731873-3891A fast, simple and environmentally friendly one-pot route to obtain carbon/SiO2 hybrid materials is reported in this work. This consists in simple mixture of carbon and silica precursors, followed by thermal annealing at different temperatures. An interpenetrating hybrid network composed of hard carbon and amorphous SiO2 nanoparticles (2–5 nm) homogeneously distributed was achieved. Increasing the annealing temperature from 600 °C up to 1200 °C, the material porosity and oxygen functional groups are gradually removed, while the amorphous nature of SiO2 is conserved. This allows to diminish the irreversible capacity during the first charge-discharge cycle and to increase the reversible capacity. An excellent cycling capability, with a reversible capacity up to 535 mA h/g at C/5 constant current rate was obtained for C/SiO2 materials used as anodes for Li-ion batteries. An atypical increase of the capacity during the first 50 cycles followed by a stable plateau up to 250 cycles was observed and related to electrolyte wettability limitation through the materials, particularly for those annealed at high temperatures which are more hydrophobic, less porous and the SiO2 nanoparticles less accessible. The SiO2 lithiation mechanism was evaluated by XRD, TEM and XPS post-mortem analyses and revealed the formation of reversible lithium silicate phases

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Le BIOCHAR et la dynamique du Phosphore

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Vanadium nitride/carbon nanotube nanocomposites as electrodes for supercapacitors

International audienceNanostructured vanadium nitride/multiwalled carbon nanotubes (VN/CNTs) composites for pseudo-capacitor applications were obtained via the sol–gel synthesis of organic or inorganic vanadium oxide precursors followed by temperature programmed ammonia reduction. Nitrogen adsorption and impedance spectroscopy measurements showed that the incorporation of CNTs during VN synthesis allows VN/CNTs nanocomposites to be obtained with higher porosity, narrower pore size distribution, better conductivity and improved electrochemical properties compared to VN without CNTs. In particular, cyclic voltammetry using three-electrode cells in KOH shows that the contribution of the redox peaks is increased when VN is associated with the carbon nanotubes. As a consequence, a capacitance increase was measured in the two-electrode system. Another important advantage of using VN/CNTs composites is their high capacitance retention (58%) at high current density (30 A g−1) compared with VN (7%), resulting in an enhancement of the energy density at high power. All these positive aspects were significantly more marked when CNTs were incorporated during VN synthesis compared to a material resulting from the physical mixture of VN with CNTs. TEM, XPS and Raman analyses point out that the enhanced electrochemical performance observed with the VN/CNTs composite could be related to an intimate contact between VN and the CNT network, a homogeneous distribution of VN on CNTs and the presence of an open mesoporous texture favouring the access of the electrolyte to the active material surface

Enhanced performance of KVPO4F0.5O0.5 in potassium batteries by carbon coating interfaces

International audiencePotassium vanadium oxyfluoride phosphate of composition KVPO4F0.5O0.5 was modified by a carbon coating to enhance its electrochemical performance. Two distinct methods were used, first, chemical vapor deposition (CVD) using acetylene gas as a carbon precursor and second, an aqueous route using an abundant, cheap, and green precursor (chitosan) followed by a pyrolysis step. The formation of a 5 to 7 nm-thick carbon coating was confirmed by transmission electron microscopy and it was found to be more homogeneous in the case of CVD using acetylene gas. Indeed, an increase of the specific surface area of one order of magnitude, low content of C sp2, and residual oxygen surface functionalities were observed when the coating was obtained using chitosan. Pristine and carbon-coated materials were compared as positive electrode materials in potassium half-cells cycled at a C/5 (C = 26.5 mA g–1) rate within a potential window of 3 to 5 V vs K+/K. The formation by CVD of a uniform carbon coating with the limited presence of surface functions was shown to improve the initial coulombic efficiency up to 87% for KVPFO4F0.5O0.5-C2H2 and to mitigate electrolyte decomposition. Thus, performance at high C-rates such as 10 C was significantly improved, with ∼50% of the initial capacity maintained after 10 cycles, whereas a fast capacity loss is observed for the pristine material

Stability of Plasma Treated Non-vulcanized Polybutadiene Surfaces: Role of Plasma Parameters and Influence of Additives

International audienceSurface modification studies of non-vulcanized BR elastomers (butadiene rubber) by low-pressure air plasma treatment and the effect on ageing and adhesion performances are presented in this paper. In particular, the influence of discharge power and distance from the glow discharge, and impact of antioxidant molecules in the BR formulation were examined. To characterize the changes to the BR surface, XPS spectroscopy, contact angle measurements, AFM nanoindentation experiments and tack measurements were utilized. Oxidation and crosslinking were the main mechanisms observed on the polymer chains regardless of the plasma conditions used. Beyond a certain threshold of plasma energy (in our case, discharge power of similar to 60 W and exposure time of similar to 30 s), a steady state was reached irrespective of the distance from the glow discharge. The presence of antioxidant molecules considerably reduced crosslinking phenomena while maintaining oxidation processes on polymer chains and increasing the nitrogen content in the near surface region. The mechanisms responsible for these differences have been identified. Interestingly, the COOH/C=O ratio changed according to the balance between oxidation and crosslinking. The hydrophobic recovery rate was mainly driven by temperature-dependent dynamics and varied according to the degree of crosslinking in the surface region. It was found to be lower in air atmosphere in the presence of antioxidant molecules. Finally, the presence of antioxidant molecules in the BR formulation allowed the adhesion performances after plasma exposure to significantly increase

Eco-friendly synthesis of SiO2 nanoparticles confined in hard carbon: A promising material with unexpected mechanism for Li-ion batteries

International audienceA fast, simple and environmentally friendly one-pot route to obtain carbon/SiO 2 hybrid materials is reported in this work. This consists in simple mixture of carbon and silica precursors, followed by thermal annealing at different temperatures. An interpenetrating hybrid network composed of hard carbon and amorphous SiO 2 nanoparticles (2e5 nm) homogeneously distributed was achieved. Increasing the annealing temperature from 600 C up to 1200 C, the material porosity and oxygen functional groups are gradually removed, while the amorphous nature of SiO 2 is conserved. This allows to diminish the irreversible capacity during the first charge-discharge cycle and to increase the reversible capacity. An excellent cycling capability, with a reversible capacity up to 535 mA hg-1 at C/5 constant current rate was obtained for C/SiO 2 materials used as anodes for Li-ion batteries. An atypical increase of the capacity during the first 50 cycles followed by a stable plateau up to 250 cycles was observed and related to electrolyte wettability limitation through the materials, particularly for those annealed at high temperatures which are more hydrophobic, less porous and the SiO 2 nanoparticles less accessible. The SiO 2 lithiation mechanism was evaluated by XRD, TEM and XPS post-mortem analyses and revealed the formation of reversible lithium silicate phases

Synthesis of sulfur-doped porous carbons by soft and hard templating processes for CO2 and H-2 adsorption

International audienceSulfur-doped porous carbons were synthesized by two synthetic approaches, i.e. a direct one (soft-template) and an indirect one (hard-template). In the soft-template approach, a phenolic resin based on phloroglucinol or resorcinol and thiophene carboxaldehyde (TCA) was self-assembled with a triblock copolymer followed by carbonization in inert atmosphere. For the second method, zeolite beta was used as hard-template and infiltrated with carbon by chemical vapor deposition (CVD) process followed by H2S treatment. Mesoporous materials with uniform pore size and moderate apparent specific surface area (up to 635 m(2) g(-1)) were obtained by soft-template route. The hard-template route, coupled with H2S post-treatment, allowed to obtain highly microporous/mesoporous materials having high apparent surface area (1700-2500 m(2) g(-1)) and high total pore volume (1.25-1.95 cm(3) g(-1)). High temperature or amounts of TCA induce a decrease of the microporosity and apparent surface area while the mesoporosity varies distinctly depending on the synthesis method used. The sulfur content could be easily modified by the amount of thiophene carboxaldehyde for the soft-templating route (up to 10.9 wt % at 600 degrees C) or by the H2S heat-treatment temperature for the hard-templating method. In the latter case, with the increase of the temperature up to 900 degrees C, high S-content was reached (up to 14.4 wt %). The influence of the carbon porosity and surface functionality on the H-2 and CO2 adsorption was evaluated. Hard-templated carbons possessing well developed microporosity adsorb the highest amounts of H-2 and CO2. The sulfur and oxygen groups lead to improvement of the hydrogen adsorption capacity and have less significant effect on CO2 storage. (C) 2016 Elsevier Inc. All rights reserved

Poly(allylamine) plasma polymer coatings for an efficient retention of Ni(II) ions by ultrafiltration membranes

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