Decoupling segmental relaxation and ionic conductivity for lithium-ion polymer electrolytes

xi+316hlm.;26c

Decoupling segmental relaxation and ionic conductivity for lithium-ion polymer electrolytes

International audienceThe use of polymer electrolytes instead of liquid organic systems is considered key for enhancing the safety of lithium batteries and may, in addition, enable the transition to high-energy lithium metal anodes. An intrinsic limitation, however, is their rather low ionic conductivity at ambient temperature. Nonetheless, it has been suggested that this might be overcome by decoupling the ion transport and the segmental relaxation of the coordinating polymer. Here, we provide an overview of the different approaches to achieve such decoupling, including a brief recapitulation of the segmental-relaxation dependent ion conduction mechanism, exemplarily focusing on the archetype of polymer electrolytes – polyethylene oxide (PEO). In fact, while the understanding of the underlying mechanisms has greatly improved within recent years, it remains rather challenging to outperform PEO-based electrolyte systems. Nonetheless, it is not impossible, as highlighted by several examples mentioned herein, especially in consideration of the extremely rich polymer chemistry and with respect to the substantial progress already achieved in designing tailored molecules with well-defined nanostructures

PEO: An immobile solvent?

Despite used for half a century as host for salt-polymer complexes, PEO is still not a fossil and due to its availability, remains regularly used as a reference in solvent-free polymer electrolytes and related electrochemical cells. Often qualified as macromolecular solvent or immobile solvent, its drawbacks (crystallinity, mechanical strength) are well identified. On the other hand, its electrolyte conductivity maxima are considered as the best possible in absence of molecular solvents or ionic liquids. The comparison of PEO/LiTFSI based on raw PEO and ultrafiltrated one, shows unambiguously the impact of unentangled oligomers not only on ionic transport but also on mechanical behavior. Conductivity, cationic transference numbers and storage modulus data go in the same direction and the cationic conductivity (O/Li = 30) is divided by 2, following PEO purification.Jean-Yves Sanchez acknowledges the CONEX Programme, funding received from Universidad Carlos III de Madrid, the European Union's Seventh Framework Programme for research, technological development and demonstration (Grant agreement nº 600371), Spanish Ministry of Economy and Competitiveness (COFUND2013-40258) and Banco Santander. Amadou Thiam acknowledges ANR for his fellowship. Yannick Molméret acknowledges KICINNO Energy for the granting of his post-doc fellowship, in the frame of the project PENLiB coordinated by Prof. Jean-Yves Sanchez

Production d'hydrogène par reformage à la vapeur et craquage catalytique de bio-huiles sur catalyseurs monolithes

nationa

Synthèse et caractérisation d'oligosiloxanes fonctionnalisés (étude de leur réticulation par voie photochimique)

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

New polysiloxane bearing imidazolium iodide side chain as electrolyte for photoelectrochemical cell

International audienceA series of new polymer electrolytes based on polydimethylsiloxane bearing 1-N-methylimidazolium-pentyl iodide side chains, (PILs) with different ionic functionality have been synthesized and characterized. In order to decrease the PILs viscosity and improve the ionic transport, ILs and organic solvent were added. The physiochemical and electrochemical properties of these PILs and their blends with ILs i.e. 1-methyl-3-propylimidazolium iodide (MPII) or 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (MPI TFSI), including density, glass transition temperature, viscosity, ionic conductivity, ionicity and diffusion coefficient were determined. Furthermore, the effect of ethylene carbonate (EC) on the physicochemical and electrochemical properties of PILs was also evaluated in terms of ionic conductivity and diffusion coefficient

Hydrogen production from crude pyrolysis oil by a sequential catalytic process

International audienceA sequential process aiming at hydrogen production was studied over two Ni-based catalysts, using crude beech-wood oil as the feed. The process alternates cracking/reforming steps, during which a H2 + CO rich stream is produced and carbon is stored on the catalyst, with regeneration steps where the carbon is combusted under oxygen. The two catalysts exhibited good performances for H2 production from bio-oil, the gaseous products stream consisting in 45–50% H2. The regeneration step was found fast and efficient, the coke being readily combusted and the catalyst activity fully recovered. A positive heat balance between the endothermic cracking/reforming reactions and the exothermic coke combustion suggests that an autothermal process could be designed. Comparison of the thermal decomposition of bio-oil (empty reactor) with the catalytic cracking revealed that they are first decomposed into primary light gases (CO, CO2, CH4, C2+) and soots. These compounds are further reformed onto the catalyst by the steam contained in bio-oil, and equilibrated via the WGS reaction. The key roles of the catalyst are therefore (i) to improve the overall bio-oil gasification into syngas, (ii) to promote steam reactions and increase hydrogen production by steam reforming and WGS and (iii) to control and determine the nature of the coke formed during the cracking/reforming step. A Ni/Al2O3 catalyst with large Ni particles was found to promote the formation of carbon filaments, whereas on a Ni–K/La2O3–Al2O3 catalyst, with a lower Ni loading and highly dispersed Ni, the carbon was essentially deposited as an amorphous carbon layer