Unveiling Interfacial Li-Ion Dynamics in Li7La3Zr2O12/PEO(LiTFSI) Composite Polymer-Ceramic Solid Electrolytes for All-Solid-State Lithium Batteries

Unlocking the full potential of solid-state electrolytes (SSEs) is key to enabling safer and more-energy dense technologies than today’s Li-ion batteries. In particular, composite materials comprising a conductive, flexible polymer matrix embedding ceramic filler particles are emerging as a good strategy to provide the combination of conductivity and mechanical and chemical stability demanded from SSEs. However, the electrochemical activity of these materials strongly depends on their polymer/ceramic interfacial Li-ion dynamics at the molecular scale, whose fundamental understanding remains elusive. While this interface has been explored for nonconductive ceramic fillers, atomistic modeling of interfaces involving a potentially more promising conductive ceramic filler is still lacking. We address this shortfall by employing molecular dynamics and enhanced Monte Carlo techniques to gain unprecedented insights into the interfacial Li-ion dynamics in a composite polymer-ceramic electrolyte, which integrates polyethylene oxide plus LiN(CF3SO2)2 lithium imide salt (LiTFSI), and Li-ion conductive cubic Li7La3Zr2O12 (LLZO) inclusions. Our simulations automatically produce the interfacial Li-ion distribution assumed in space-charge models and, for the first time, a long-range impact of the garnet surface on the Li-ion diffusivity is unveiled. Based on our calculations and experimental measurements of tensile strength and ionic conductivity, we are able to explain a previously reported drop in conductivity at a critical filler fraction well below the theoretical percolation threshold. Our results pave the way for the computational modeling of other conductive filler/polymer combinations and the rational design of composite SSEs.-Juan de la Cierva grant IJC2018-037214-I, -PID2019-106519RB-I00, as -HPC-Europa3 grant HPC17ERWTO -AI in BCAM, EXP. 2019/004

Les modifications des milieux aquatiques de Camargue au cours des 30 dernières années

Les auteurs, s'appuyant sur les observations faites par de nombreux chercheurs depuis 1935 et sur leurs propres travaux commencés en 1953, décrivent de façon succinte les modifications de quelques étangs ou marais camarguais pris comme exemples. Selon la localisation du milieu aquatique, les (variations sont dues à l'influence de l'homme (salines et rizières) ou à celle du climat (précipitations atmosphériques). La flore et la faune aquatique subissent des changements qui se reproduisent identiques à eux-mêmes lorsque les conditions de milieu se modifient de la même façon. Ainsi, pour tel cycle annuel de salinité et pour une eau temporaire, la flore et la faune seront composés de telles espèces. Pour tel autre cycle de salinité et pour une eau permanente, les composantes faunistiques et floristiques seront différentes, mais, si les facteurs du milieu sont à nouveau ce qu'ils étaient lors du premier cycle, on retrouve les plantes et les animaux qui le caractérisaient. L'augmentation de la concentration en sel provoque une diminution du nombre des espèces, mais il y a une prolifération du nombre des individus. La diminution de la concentration, jointe à la permanence du milieu, entraîne une augmentation du nombre des espèces, mais avec relativement peu d'individus. La productivité primaire est cependant considérablement accrue. Les espèces qui donnent à la Camargue son originalité ne se trouvent qu'en eaux saumâtres. Dans les eaux adoucies, on ne rencontre que des espèces banales. Toutes les modifications observées apparaissent aux auteurs comme réversibles : il serait néanmoins urgent de préparer un aménagement du delta sur des bases scientifiques, qui lui conserverait son originalité sans nuire aux intérêts des riziculteurs ou des industries salinières

Xanthate-mediated copolymerization of vinyl monomers for amphiphilic and double-hydrophilic block copolymers with poly(ethylene glycol)

Two xanthate end-functional poly(ethylene glycol)s (PEGs) were tested as macromolecular chain-transfer agents (macroCTA) in the reversible addition-fragmentation transfer-mediated polymerization of vinyl acetate (VAc) and N-vinylpyrrolidone. The macroCTA leaving group played a determining role in the preparation of the block copolymers. PEG-b-PVAc and PEG-b-PVP diblock copolymers were obtained when the macroCTA had a propionyl ester leaving group, whereas under the same experimental conditions the macroCTA with a phenylacetyl ester leaving group inhibited the polymerization. In situ 1H NMR spectroscopy polymerizations were performed with low molecular weight xanthate analogues to investigate the cause of inhibition. Block copolymers were prepared with the macroCTA which did not inhibit the polymerization and were characterized via size exclusion chromatography, high-performance liquid chromatography, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The ability to produce narrowly distributed (PDI <1.4) block copolymers end capped with a xanthate moiety with little to no homopolymer contaminant is presented

Xanthate-mediated copolymerization of vinyl monomers for amphiphilic and double-hydrophilic block copolymers with poly(ethylene glycol)

Two xanthate end-functional poly(ethylene glycol)s (PEGs) were tested as macromolecular chain-transfer agents (macroCTA) in the reversible addition-fragmentation transfer-mediated polymerization of vinyl acetate (VAc) and N-vinylpyrrolidone. The macroCTA leaving group played a determining role in the preparation of the block copolymers. PEG-b-PVAc and PEG-è-PVP diblock copolymers were obtained when the macroCTA had a propionyl ester leaving group, whereas under the same experimental conditions the macroCTA with a phenylacetyl ester leaving group inhibited the polymerization. In situ 1H NMR spectroscopy polymerizations were performed with low molecular weight xanthate analogues to investigate the cause of inhibition. Block copolymers were prepared with the macroCTA which did not inhibit the polymerization and were characterized via size exclusion chromatography, high-performance liquid chromatography, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The ability to produce narrowly distributed (PDI < 1.4) block copolymers end capped with a xanthate moiety with little to no homopolymer contaminant is presented. © 2007 American Chemical Society.Articl

Xanthate-mediated copolymerization of vinyl monomers for amphiphilic and double-hydrophilic block copolymers with poly(ethylene glycol)

Two xanthate end-functional poly(ethylene glycol)s (PEGs) were tested as macromolecular chain-transfer agents (macroCTA) in the reversible addition-fragmentation transfer-mediated polymerization of vinyl acetate (VAc) and N-vinylpyrrolidone. The macroCTA leaving group played a determining role in the preparation of the block copolymers. PEG-b-PVAc and PEG-b-PVP diblock copolymers were obtained when the macroCTA had a propionyl ester leaving group, whereas under the same experimental conditions the macroCTA with a phenylacetyl ester leaving group inhibited the polymerization. In situ 1H NMR spectroscopy polymerizations were performed with low molecular weight xanthate analogues to investigate the cause of inhibition. Block copolymers were prepared with the macroCTA which did not inhibit the polymerization and were characterized via size exclusion chromatography, high-performance liquid chromatography, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The ability to produce narrowly distributed (PDI &lt;1.4) block copolymers end capped with a xanthate moiety with little to no homopolymer contaminant is presented

Investigating the dendritic growth during full cell cycling of garnet electrolyte in direct contact with Li metal.

All-solid-state batteries including a garnet ceramic as electrolyte are potential candidates to replace the currently used Li-ion technology, as they offer safer operation and higher energy storage performances. However, the development of ceramic electrolyte batteries faces several challenges at the electrode/electrolyte interfaces, which need to withstand high current densities to enable competing C-rates. In this work, we investigate the limits of the anode/electrolyte interface in a full cell that includes a Li-metal anode, LiFePO4 cathode, and garnet ceramic electrolyte. The addition of a liquid interfacial layer between the cathode and the ceramic electrolyte is found to be a prerequisite to achieve low interfacial resistance and to enable full use of the active material contained in the porous electrode. Reproducible and constant discharge capacities are extracted from the cathode active material during the first 20 cycles, revealing high efficiency of the garnet as electrolyte and the interfaces, but prolonged cycling leads to abrupt cell failure. By using a combination of structural and chemical characterization techniques, such as SEM and solid-state NMR, as well as electrochemical and impedance spectroscopy, it is demonstrated that a sudden impedance drop occurs in the cell due to the formation of metallic Li and its propagation within the ceramic electrolyte. This degradation process is originated at the interface between the Li-metal anode and the ceramic electrolyte layer and leads to electromechanical failure and cell short-circuit. Improvement of the performances is observed when cycling the full cell at 55 °C, as the Li-metal softening favors the interfacial contact. Various degradation mechanisms are proposed to explain this behavior