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Lithium sulphur batteries are promising candidates for upcoming/future energy storage systems due to their theoretical specific energy (2500 Wh kg−1). Poor cycle life and low capacity retention are main issues restraining their commercialization. To achieve high energy density, metallic lithium or concentrated alloy negatives are required wherein both the challenge of high reactivity leading to degradation, and safety issues have to be dealt with. LiNO3 has been reported as an electrolyte additive to produce passivation layer on the metallic lithium anode. However, the passivation layer thickness cannot be controlled. In order to have similar passivation effect with controlled thickness and to avoid undesirable reaction on the surface of the lithium metal, Li3N protective layers has been investigated. This study demonstrates the effect of coating techniques and feasibility of Li3N protective layers for Li metal anodes in Li-S cells using just a standard sulphur/ carbon composite electrode, thereby independent from the effects of binders or any porous cathode architecture. A first approach to study the surface morphology of Li with Li3N layers in Li-S batteries has been made. Improved cycling efficiency and good lithium plating/stripping characteristics were observed with a smooth surface morphology of Li metal. A viable in-situ approach of depositing Li3N layer on the Li metal anode using ([(CH3)3SiN3]) as electrolyte additive is proposed.

The nature of the alkaline electrolyte (based on KOH, NaOH, LiOH), in which Co{sub 3}O{sub 4} spinel type phases are synthesized by electrooxidation of CoO, is shown to play a key role on the composition, the structure and the electronic conductivity of the materials. In the materials, prepared in pure LiOH electrolyte or in mixed ternary electrolyte (KOH, NaOH, LiOH), Co{sup 4+} ions are present in the octahedral framework, which entails electronic delocalization in the cobalt T{sub 2g} band and a high conductivity. The structure of the sample, synthesized in KOH, is on the opposite closer to that of ideal Co{sub 3}O{sub 4}, with only Co{sup 3+} in the octahedral sublattice, which leads to a semi-conducting behavior. Whatever the initial material, a thermal treatment induces an increase of the Co{sup 4+}/Co{sup 3+} ratio in the octahedral network, resulting in a significant increase of the electronic conductivity. - Graphical abstract: In 'Co{sub 3}O{sub 4}' type spinel phases synthesized by eleectrooxidation, the nature of the alkaline electrolyte allows to monitor the amounts of hydrogen and lithium, inserted in spinel framework and therefore the electronic conductivity. Whatever the initial synthesis electrolyte, a moderate thermal treatment of the materials induces a significant increase ofmore » the electronic conductivity, due to a structural reorganization (illustrated by the evolution of the cell parameter) and an increase of the Co{sup 4+}/Co{sup 3+} ratio in the octahedral framework.« less

International audience; A series of “Li1+z/2(Ni0.425Mn0.425Co0.15)1−z/2O2−zFz” materials was prepared by a coprecipitation route and their structure was characterized using X-ray diffraction (XRD), as well as 7Li and 19F Magic Angle Spinning (MAS) NMR spectroscopy. Two hypotheses were considered: (i) formation of layered oxyfluoride materials and (ii) formation of a mixture between the layered material and LiF. Structural parameters were refined by the Rietveld method, using XRD diffraction data. The refinement results did not allow us to choose between these two hypotheses: no significant change in crystallinity and structural parameters was observed irrespective of the fluorine ratio. 7Li and 19F MAS NMR analyses showed signals with isotropic positions characteristic of LiF, but envelopes characteristic of very strong dipolar interactions with the electron spins of the material, demonstrating that LiF was not incorporated into the layered oxide structure but was instead present as a coating.

Mixtures of tin(II) chloride and tin(II)-sodium–potassium chlorides were converted into phosphate salts by reaction with ammonium dihydrogen-phosphate at 400 °C. Element analyses showed that no loss occurred during the treatment, and Mossbauer and wet analyses indicated no change in tin valence. The converted tin phosphate and tin–sodium–potassium phosphates were then dissolved into silicate glasses at 1350 °C without loss. Structural analyses were realized with 31P, 29Si, 119Sn NMR and 119Sn Mossbauer, which revealed a complete dissociation of tin phosphate into the silicates. Phosphate units consisted in ortho- and pyro-phosphates. Tin(II) was partially oxidized into tin(IV), but there was no evidence for a phase separation into SnO2 or SnP2O7, tin being mainly bonded to silicate units. These results are discussed in terms of O2− exchange between phosphate and silicate units during the melting process.

x SnO–(100 – x) P2O5 glasses (0.30 ≤ x ≤ 0.75) were prepared under argon atmosphere. The Sn2+/Sntotal ratio, determined by wet chemical analysis, varies from 90 to 99% depending on glass composition. Glass transition temperatures are very low, and no effect of Sn4+could be detected. Glass structure was characterised with 31P and 119Sn NMR. There is no evidence for a specific Qn site bonded to Sn4+, but taking into account the amount of Sn4+ enabled to obtain Qn distribution close to calculated values for binary site distribution. 119Sn NMR spectra were recorded in static conditions. Chemical shift anisotropy (CSA) of glasses were compared to crystalline reference compounds. Tin(II) local environment in glasses is close to a trigonal pyramid, and Sn4+ NMR parameters are in accordance with a local environment similar to SnP2O7. To cite this article: E. Bekaert et al., C. R. Chimie 7 (2004).