Olivier Mentré

Ethoxycarbonyl-based organic electrode for Li-batteries.

Currently, batteries are being both considered and utilized in a variety of large-scale applications. Materials sustainability stands as a key issue for future generations of batteries. One alternative to the use of a finite supply of mined materials is the use of renewable organic materials. However, before addressing issues regarding the sustainability of a given organic electrode, fundamental questions relating to the structure-function relationships between organic components and battery performance must first be explored. Herein we report the synthesis, characterization, and device performance of an organic salt, lithium 2,6-bis(ethoxycarbonyl)-3,7-dioxo-3,7-dihydro-s-indacene-1,5-bis(olate), capable of reversibly intercalating with minimal polarization 1.8 Li per unit formula over two main voltage plateaus located at approximately 1.96 and approximately 1.67 V (vs. Li/Li(+)), leading to an overall capacity of 125 mAh/g. Proton NMR and in situ XRD analyses of battery cycling versus Li at room temperature reveal that the insertion-deinsertion process is fully reversible with the dips in the voltage-composition traces, which are associated with changes in the 3D structural packing of the electrochemically active molecules.

Anion-centered tetrahedra in inorganic compounds.

Sergey V. Krivovichev,*,†,‡ Olivier Mentre,́ Oleg I. Siidra,† Marie Colmont, and Stanislav K. Filatov† †St. Petersburg State University, Department of Crystallography, University Emb. 7/9, 199034 St. Petersburg, Russia ‡Institute of Silicate Chemistry, Russian Academy of Sciences, Makarova Emb. 6, 199034 St. Petersburg, Russia UCCS, Equipe de Chimie du Solide, UMR CNRS 8181, ENSC LilleUST Lille, BP 90108, 59652 Villeneuve d’Ascq Cedex, France

α-Na3M2(PO4)3 (M = Ti, Fe): Absolute Cationic Ordering in NASICON-Type Phases

The structure of the fully ordered α-Na(3)Ti(2)(PO(4))(3) NASICON compound was elucidated using high-quality single-crystal data. The cation/vacancy distribution forms a homogeneous 3D arrangement and could represent the absolute cationic ordering available in the full Na(3)M(2)(PO(4))(3) series, as verified for M = Fe. For M = Ti, the reversible α → γ transition was observed at 85 °C, leading to the standard disordered R ̅3c γ model. Through JPDF analysis, the most probable Na(+) zigzag M(2)-M(1) diffusion scheme was directly deduced using our accurate crystallographic data.

High-Potential Reversible Li Deintercalation in a Substituted Tetrahydroxy-p-benzoquinone Dilithium Salt: An Experimental and Theoretical Study

Efficient organic Li-ion batteries require air-stable lithiated organic structures that can reversibly deintercalate Li at sufficiently high potentials. To date, most of the cathode materials reported in the literature are typically synthesized in their fully oxidized form, which restricts the operating potential of such materials and requires use of an anode material in its lithiated state. Reduced forms of quinonic structures could represent examples of lithiated organic-based cathodes that can deintercalate Li(+) at potentials higher than 3 V thanks to substituent effects. Having previously recognized the unique electrochemical properties of the C(6)O(6)-type ring, we have now designed and then elaborated, through a simple three-step method, lithiated 3,6-dihydroxy-2,5-dimethoxy-p-benzoquinone, a new redox amphoteric system derived from the tetralithium salt of tetrahydroxy-p-benzoquinone. Electrochemical investigations revealed that such an air-stable salt can reversibly deintercalate one Li(+) ion on charging with a practical capacity of about 100 mAh g(-1) at about 3 V, albeit with a polarization effect. Better capacity retention was obtained by simply adding an adsorbing additive. A tetrahydrated form of the studied salt was also characterized by XRD and first-principles calculations. Various levels of theory were probed, including DFT with classical functionals (LDA, GGA, PBEsol, revPBE) and models for dispersion corrections to DFT. One of the modified dispersion-corrected DFT schemes, related to a rescaling of both van der Waals radii and s(6) parameter, provides significant improvements to the description of this kind of crystal over other treatments. We then applied this optimized approach to the screening of hypothetical frameworks for the delithiated phases and to search for the anhydrous structure.

Electrochemical Reactivity of Lithium Chloranilate vs Li and Crystal Structures of the Hydrated Phases

Li-ion batteries based on active organic electrode materials may present an alternative route to the current battery technology, particularly in terms of recycling cost. Here, we report preliminary data regarding the electrochemical behavior of Li 2 C 6 O 4 Cl 2 obtained by dehydration of the dilithium chloranilate monohydrate, which is formed by spontaneous dehydration of the Li 2 C 6 O 4 Cl 2 .∼6H 2 O phase. Electrochemically tested vs Li, the anhydrous chloranilate displays a reversible capacity of 200 mAh g -1 at an average potential of 2.3 V, which slightly decays upon cycling as opposed to Li 2 C 6 O 4 Cl 2 ·H 2 O. Moreover, thermal recycling of chloranilate phases leads to the LiCl formation, which is a benign salt.

A genuine two-dimensional Ising ferromagnet with magnetically driven re-entrant transition.

Inorganic compounds made up of low-dimensional ferromagnetic (FM) units display fascinating properties and provide a rich opportunity to investigate FM ground states, fieldinduced transitions, and magnetization steps. Even the spin-valve effect, realized in multilayer thin films, is found in the magnetic metal Ca3Ru2O7 [5] and its Cr-doped analogue in which FM double-perovskite layers are antiferromagnetically coupled. The inorganic compound Cr2Si2Te6, also consisting of FM layers, turns out to be a unique example of a bulk 2D FM Ising system. It is a great synthetic challenge to discover new magnetic transition-metal oxides made up of FM layers. In searching for such materials, a rational approach rather than by a blind exploration of chemical systems should be used. In general, a transition-metal cation at a coordinate site with three-fold or higher rotational symmetry can lead to uniaxial magnetism if its d electron count and spin state are such that there occurs an unevenly-filled degenerate level, as found for high-spin Fe ions at linear-coordinate sites and high-spin Co and Co ions at trigonal-prismatic sites. In principle, high-spin FeO6 octahedra can support uniaxial magnetism as long as they possess three-fold rotational symmetry. It can be imagined that isolated FM layers form from such FeO6 octahedra by edge-sharing because the Fe-O-Fe angle will be close to 908 so that the nearest-neighbor spin exchange would be FM. Our guided search for such a magnetic system led to the synthesis of BaFe2(PO4)2 that turns out to be the first oxide 2D Ising ferromagnet. It consists of FM honeycomb layers of edge-sharing FeO6 octahedra containing high-spin Fe 2+ ions. Such FeO6 octahedra showing uniaxial magnetism are expected to be susceptible to Jahn–Teller (JT) instability. Indeed, on cooling, BaFe2(PO4)2 undergoes a rare re-entrant structural transition owing to the competition between uniaxial magnetism and the JT distortion.

Unprecedented robust antiferromagnetism in fluorinated hexagonal perovskites.

The diversification of antiferromagnetic (AFM) oxides with high Néel temperature is of fundamental as well as technical interest if one considers the need for robust AFM in the field of spin-tronics (exchange bias, multiferroics, etc.). Within the broad series of so-called hexagonal perovskites (HP), the existence of face-sharing octahedral units drastically lowers the strength of magnetic exchanges as compared to corner-sharing octahedral edifices. Here, we show that the partial introduction of F(-) in several Fe-based HP types leads to a drastic increase of the AFM ordering close to the highest values reported in iron oxides (T(N) ≈ 700 K). Our experimental results are supported by ab initio calculations. The T(N) increase is explained by the structural effect of the aliovalent F(-) for O(2-) substitution occurring in preferred anionic positions: it leads to local changes of the Fe-O-Fe connectivity and to chemical reduction into predominant Fe(3+), both responsible for drastic magnetic changes.

Channel structure in the new BiCoPO5. Comparison with BiNiPO5. Crystal structure, lone pair localisation and infrared characterisation

Abstract The new compound BiCoPO 5 , monoclinic, P2 1 /n, a = 7.2470(1) A, b = 11.2851(2) A, c = 5.2260(1) A and β = 107.843(1) °, Z = 4, was synthesised and structurally characterised by powder X- ray diffraction and infrared spectroscopy. It is isostructural with bismuth nickel oxyphosphate BiNiOPO 4 . The crystal structure is built from a complex tridimensional assembly of (Co/Ni) 2 O 10 dimers linked by PO 4 groups. This forms large tunnels running along c which host Bi 3+ cations. Smaller tunnels running along a and crossing the latter were also evidenced. It is noteworthy that the original BiNiPO 5 lattice is appreciably increased with Co 2+ cations as the transition metal. This feature is essentially pointed out by the Co-O longer distances. The Bi 3+ cation is surrounded by a strongly distorted oxygen octahedron. Reducing the Bi O bonds to the three shortest, Bi environment can be considered as tetrahedral considering the BiO 3 Lp polyhedron, Lp = 6s 2 lone pair (Lp). The lone pair localisation was performed from electrostatic interactions and revealed Lp - Bi distance of 0.68 A and 0.58 A, for Co 2+ and Ni 2+ compounds respectively. The infrared spectra of the two compounds are essentially the same and only show slight shifts of the significant bands.

From the mixed valent 6H-Ba3Ru5.5+2NaO9 to the 6H-Ba3(Ru1.69C0.31)(Na0.95Ru0.05)O8.69 oxycarbonate compound

Abstract Ba3Ru2NaO9 single crystals have been prepared by electrosynthesis in molten NaOH. It adopts a 6H perovskite crystal structure, a=5.8645(6) A, c=14.440(2) A, space group P63/mmc, Z=2, R1=1.84%, wR2=3.91%. The mean ruthenium valence is 5.5+ for a unique Ru crystallographic site suggesting itinerant electrons within Ru2O9 dimers. Previously to our study, a Ru(V)/Ru(VI) charge ordering has been evidenced at 210 K by both single crystal XRD and susceptibility measurements. The resistivity measurement versus temperature performed in the current work shows a brutal R increase at this temperature. Below this temperature, a residual magnetic moment is observed on magnetization plots but has not been observed at 2 K. An additional anomaly is also evidenced on the R versus T plot, at T2=50 K. It is related to a magnetic transition of questionable origin appearing around the same temperature. Attempts to prepare the title compound by solid state reaction lead to a new related-phase. In fact, combined X-ray and neutron diffraction data unambiguously show the presence of CO2−3 anions in the material. Thus, part of the Ru2O9 dimers are replaced by one RuO5 square pyramid and one CO3 group leading to the nominal Ba3(Ru1.69C0.31)(Na0.95Ru0.05)O8.69 formula. The carbonates typical vibration bands have been observed by infrared spectroscopy and clearly distinguished from possible BaCO3 impurity bands. Compared to the ideal 6H-Ba3Ru5.5+2NaO9, the oxycarbonate main characteristic is the ruthenium +5.28 mean valence. Numerically, such a valence can be obtained considering all the dimeric ruthenium with a +5 oxidation number and the RuO5 and (Na/Ru)O6 corner sharing octahedra to be +6. The structure has also been refined by Rietveld analysis of powder neutron diffraction data recorded at 20 K. No structural difference is observed at low temperature. The Ba/Na/Ru oxycarbonate shows sensitive modifications of its physical properties as compared to Ba3Ru2NaO9. Its conductivity obeys an Arrhenius law and no transitions is observed on cooling. The magnetic susceptibility shows a Curie–Weiss behavior until 120 K, afterward, a weak magnetic moment appears and may be due to the RuO5 magnetic interaction with the other magnetic moieties. Electron diffraction patterns show a superstructure phenomenon in the (a,b) plane for Ba3Ru2NaO9 while diffuse lines parallel to c ∗ are observed for the oxycarbonate. The HREM contrast has been satisfactorily simulated and explained on the basis of Ba contrast towards lighter species within the 6H blocks but does not allow to distinguish between both compounds.

Across the Structural Re-Entrant Transition in BaFe2(PO4)2: Influence of the Two-Dimensional Ferromagnetism

BaFe2(PO4)2 was recently prepared by hydrothermal synthesis and identified as the first two-dimensional (2D) Ising ferromagnetic oxide, in which honeycomb layers made up of edge-sharing FeO6 octahedra containing high-spin Fe(2+) ions (S = 2) are isolated by PO4 groups and Ba(2+) cations. BaFe2(PO4)2 has a trigonal R-3 structure at room temperature but adopts a triclinic P-1 structure below 140 K due to the Jahn-Teller (JT) instability arising from the (t2g)(4)(eg)(2) configuration. The triclinic crystal structure was refined to find significantly distorted Fe(2+)O6 octahedra in the honeycomb layers while the distortion amplitude QJT was estimated to 0.019 Å. The JT stabilization energy is estimated to be ∼7 meV per formula unit by DFT calculations. Below ∼70 K, very close to the ferromagnetic transition temperature Tc = 65.5 K, the structure of BaFe2(PO4)2 returns to a trigonal R-3 structure in the presence of significant ferromagnetic domains. This rare re-entrant structural transition is accompanied by a discontinuous change in the quadrupolar splitting of Fe(2+), as determined by Mössbauer spectroscopy. EPR measurements show the presence of magnetic domains well above Tc , as expected for a ferromagnetic 2D Ising system, and support that the magnetism of BaFe2(PO4)2 is uniaxial (g⊥ = 0).