Novel positive electrode architecture for rechargeable lithium/sulfur batteries

International audienceThe lithium/sulfur battery is a very promising technology for high energy applications. Among other advantages, this electrochemical system has a high theoretical specific capacity of 1675 mAh g−1, but suffers from several drawbacks: poor elemental sulfur conductivity, active material dissolution and use of the highly reactive lithium metal electrode. More particularly, the discharge capacity is known to be dictated by the short lithium polysulfide precipitation. These poorly soluble and highly insulating species are produced at the end of discharge, and are responsible for the positive electrode passivation and the early end of discharge. Nevertheless, the discharge capacity can be improved by working on the positive electrode specific surface area and morphology, as well as on the electrolyte composition. In this paper, we focused on the positive electrode issue. To this purpose, various current collector structures have been tested in order to achieve a high positive electrode surface area and a stable morphology during cycling. We demonstrated that the discharge capacity could be increased up to 1400 mAh g−1 thanks to the use of carbon foam. As well, the capacity fading could be dramatically decreased in comparison with the one obtained for conventional sulfur composite electrodes

New insight into the working mechanism of lithium–sulfur batteries: in situ and operando X-ray diffraction characterization

International audienceIn order to improve the electrochemical performances of lithium–sulfur batteries, it is crucial to understand profoundly their working mechanism and the limitation factors. This communication presents synchrotron-based in situ XRD studies of structural modifications occurring inside the cell upon cycling, since the active material changes constantly its form between solid and liquid phases.Graphical abstract: New insight into the working mechanism of lithium–sulfur batteries: in situ and operando X-ray diffraction characterizatio

Polyphased mesozoic rifting from the Atlas to the north-west Africa paleomargin.

24 pagesInternational audienceBased on the interpretation of geological maps, seismic reflection and well data complemented with a bibliographic compilation and field work in the Rif, we investigate the factors that control the rift initiation, its development and the formation of oceanic crust in NW Africa. From SE to NW, we examine the Western Sahara Atlas, the Tendrara, the Guercif, and the Rif basins, to establish their geodynamic evolution in relation with the Mesozoic formation of the Central Atlantic and Maghrebian Tethys oceans, respectively. The Triassic extension was diffuse and developed over Lower Carboniferous horst-and-graben structures formed in the NW passive margin of Gondwana and involved in the subsequent late Carboniferous – early Permian Variscan orogenic system; suggesting that, at the onset of the Triassic rifting, the lithosphere was thermally re-equilibrated and replaced by more fertile lithospheric mantle. Afterwards, extension resumed in the Atlas system during middle to late Pliensbachian and finished during Toarcian. In the Rif and Guercif basins, the extension began later, mainly during the Toarcian, climaxing during Middle Jurassic times with the exhumation along low-angle extensional faults of CAMP gabbroic bodies and the final mantle exhumation during Upper Jurassic in the Rif. The study evidences the prominent role of the Variscan structural and thermal inheritance on the subsequent deformation events. Accordingly, the Paleozoic inverted basins and horsts localized the Triassic extension. From that, the opening of the Central Atlantic and Maghrebian Tethys oceans activated, respectively, the SE (Atlas) and NW (Tethys) rifted segments of the weakened continental crust where the Jurassic extension was gradually distributed. This led to the final formation of an oceanic domain in the NW paleomargin of Africa

Limits in point to point resolution of MOS based pixels detector arrays

International audienceIn high energy physics point-to-point resolution is a key prerequisite for particle detector pixel arrays. Current and future experiments require the development of inner-detectors able to resolve the tracks of particles down to the micron range. Present-day technologies, although not fully implemented in actual detectors, can reach a 5-μm limit, this limit being based on statistical measurements, with a pixel-pitch in the 10 μm range. This paper is devoted to the evaluation of the building blocks for use in pixel arrays enabling accurate tracking of charged particles. Basing us on simulations we will make here a quantitative evaluation of the physical and technological limits in pixel size. Attempts to design small pixels based on SOI technology will be briefly recalled here. A design based on CMOS compatible technologies that allow a reduction of the pixel size below the micrometer is introduced here. Its physical principle relies on a buried carrier-localizing collecting gate. The fabrication process needed by this pixel design can be based on existing process steps used in silicon microelectronics. The pixel characteristics will be discussed as well as the design of pixel arrays. The existing bottlenecks and how to overcome them will be discussed in the light of recent ion implantation and material characterization experiments

Guided tissue regeneration membranes with controlled delivery properties of chlorhexidine by their functionalization with cyclodextrins

In parodontology, guided tissue regeneration (GTR) is a new technique to cure periodontal lesions. Where the association of the GTR with an antimicrobial agent does not yield optimal results, we used the properties of cyclodextrins (CDs) to improve the membrane used in RTG to control the release and to increase the quantity of antimicrobial agent stocked on the membrane. We successed in fixing 14%-wt of cyclodextrin polymer on polyvinylidene difluoride(PVDF) membranes thank to citric acid (CTR) as crosslinking agent. We studied the complexation of chlorhexidine diacetate (CHX), the antiseptic agent used in this study, with CDs in UV-spectrophotometry and ROESY NMR. We observed complexation of CHX by b, c, hydroxypropylated (HP) bCD. We studied the biological properties of the cyclodextrin polymer onto (PVDF) membranes and observed that the CDs-polymer is not harmful for the cells. Moreover it stimulates their growth with native CD. A kinetic of release of the CHX was performed. Raw membranes released all CHX stocked in few hours, whereas grafted membranes released more than tenfold this quantity during 60–80 days