Ionic liquids to monitor the nano-structuration and the surface functionalization of material electrodes: a proof of concept applied to cobalt oxyhydroxide.

This paper reports on an innovative and efficient approach based on the use of ionic liquids to govern the nano-structuration of HCoO2, in order to optimize the porosity and enhance the ionic diffusion through the electrode materials. In this work, we show that (1-pentyl-3-methyl-imidazolium bromide (PMIMBr) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4)) ionic liquids (ILs) used as templates during the synthesis orientate the nanoparticle aggregation which leads to increase of the porosity and the average pore size of the electrode material. It is also demonstrated that the ILs are strongly bonded to the HCoO2 surface, leading to surface functionalized HCoO2 materials, also called nanohybrids. This surface tailoring stabilizes the material upon cycling and shifts the oxidation potential linked to the Co(iii)/Co(iv) redox couple to lower voltage in an alkaline 5 M KOH electrolyte. The surface and porosity optimizations facilitate the ionic diffusion through the material, improve the electron transfer ability within the electrode and lead to greatly enhanced specific capacity in both alkaline 5 M-KOH and neutral 0.5 M-K2SO4 aqueous electrolytes (66.7 mA h g-1 and 47.5 mA h g-1 respectively for HCoO2-PMIMBr and HCoO2-EMIMBF4 compared to 18.1 mA h g-1 for bare HCoO2 in 5 M-KOH at 1 A g-1).

P2-Na(x)Mn(1/2)Fe(1/2)O2 phase used as positive electrode in Na batteries: structural changes induced by the electrochemical (de)intercalation process.

The electrochemical properties of the P2-type NaxMn1/2Fe1/2O2 (x = 0.62) phase used as a positive electrode in Na batteries were tested in various voltage ranges at C/20. We show that, even if the highest capacity is obtained for the first cycles between 1.5 and 4.3 V, the best capacity after 50 cycles is obtained while cycling between 1.5 and 4.0 V (120 mAh g(-1)). The structural changes occurring in the material during the (de)intercalation were studied by operando in situ X-ray powder diffraction (XRPD) and ex situ synchrotron XRPD. We show that a phase with an orthorhombic P'2-type structure is formed for x ≈ 1, due to the cooperative Jahn-Teller effect of the Mn(3+) ions. P2 structure type stacking is observed for 0.35 < x < 0.82, while above 4.0 V, a new phase appears. A full indexation of the XRPD pattern of this latter phase was not possible because of the broadening of the diffraction peaks. However, a much shorter interslab distance was found that may imply a gliding of the MO2 slab occurring at high voltage. Raman spectroscopy was used as a local probe and showed that in this new phase the MO2 layers are maintained, but the phase exhibits a strong degree of disorder.

Iron(III) phosphates obtained by thermal treatment of the Tavorite-type FePO4·H2O material: structures and electrochemical properties in lithium batteries.

Thermal treatment of the Tavorite-type material FePO(4)·H(2)O leads to the formation of two crystallized iron phosphates, very similar in structure. Their structural description is proposed taking into account results obtained from complementary characterization tools (thermal analyses, diffraction, and spectroscopy). These structures are similar to that of the pristine material FePO(4)·H(2)O: iron atoms are distributed between the chains of corner-sharing FeO(6) octahedra observed in FePO(4)·H(2)O and the octahedra from the tunnels previously empty, in good agreement with the formation of a Fe(4/3)PO(4)(OH)-type phase. The formation of an extra disordered phase was also proposed. These samples obtained by thermal-treatment of FePO(4)·H(2)O also intercalate lithium ions through the reduction of Fe(3+) to Fe(2+) at an average voltage of ~2.6 V (vs Li(+)/Li), with a good cyclability and a reversible capacity around 120 mA h g(-1) (>160 mA h g(-1) during the first discharge).

Interactions in self-organized nanoporous organic crystals.

This Letter reports on the structural analysis of a self-assembly material, the prototype host-guest urea-alkane nanoporous crystal. Different spectroscopic techniques, under hydrostatic pressure, reveal a totally unexpected ordered phase where ordering does not require any apparent deformation of the host. This fundamental observation raises the question of the actual interactions in other similar supramolecular or biological tubular systems.

First one-dimensional stress-strain experiments inside an aperiodic inclusion compound: evidence of depinning effects.

This Letter reports on the first observation of depinning under hydrostatic pressure of the guest and host sublattices inside the aperiodic nonadecane-urea inclusion compound. This leads to a unique way for a direct determination of the one-dimensional interguest interaction (1 N/m for nonadecane).