Y. Piffard

LiMBO3 (M=Mn, Fe, Co):: synthesis, crystal structure and lithium deinsertion/insertion properties

Abstract The LiMBO3 (M=Mn, Fe, Co) compounds were synthesized by a solid state reaction. LiFeBO3 and h-LiMnBO3 crystal structures were determined from single crystal data. LiFeBO3 exhibits the same structure as that of other already described LiMBO3 compounds (M=Mg, Mn, Co, Zn). The structure of h-LiMnBO3 is isotypic with the hexagonal form of LiCdBO3. The electrochemical study shows that a very small amount of lithium (less than 0.04 Li per formula unit) can be deinserted reversibly from the three compounds. According to the thermodynamic study performed in the case of LiFeBO3, the Fe3+/Fe2+ redox couple lies between 3.1 and 2.9 V/Li, demonstrating an important inductive effect of the BO3 group.

Electrochemically synthesized vanadium oxides as lithium insertion hosts

The electrochemical oxidation of vanadyl cations in aqueous solution leads to a solid deposit on the working electrode, called electrolytic vanadium oxide (e-V2O5). The electrodeposition reaction occurs in two steps including an oxidation into soluble species followed by a precipitation. Electrodeposited compounds are mixed valence, hydrated vanadic acids. Their chemical formula can be written H0.4V2O5.2−δ·nH2O with 0.04<δ<0.2 and 0<n<1.8. These two latter parameters depend on the current density applied during electrodeposition, the duration and the temperature of a subsequent mild thermal treatment in air. e-V2O5 materials are porous, poorly crystallized layered compounds. At 260°C, they become completely anhydrous and undergo a phase transformation into α-V2O5. The electrochemical intercalation of lithium into these compounds shows two main single phase phenomena near 2.6 and 3.1 V/Li. This reduction induces a lengthening of the average vanadium oxygen bond, and a decrease of the lithium diffusion coefficient. e-V2O5 compounds reversibly intercalate 1.4≅Li per formula unit at an average voltage of 2.8≅V/Li, at a rate of C/50 in the 4–2 V range, and this capacity is maintained during several tens of discharge/charge cycles. The electrochemical behavior is slightly dependent on the VIV content and the crystallization state of the compounds.

New amorphous oxides as high capacity negative electrodes for lithium batteries: the LixMVO4 (M = Ni, Co, Cd, Zn; 1 < x ≤ 8) series

Abstract The crystallized precursors LiMVO 4 (M = Co, Ni, Cd, Zn) are irreversibly transformed to lithiated amorphous oxides Li x MVO 4 ( x close to 8) during the first Li insertion in a lithium battery. Under low rate, these amorphous oxides cycle large amounts of Li per formula unit in the 0.02–3 V range (versus Li), with an average voltage in the order of 0.6 V for Li insertion and 1.4 V for Li extraction. In the case of Li x NiVO 4 at first Li extraction, for example, Δ x = 6.6 and Q = 980 Ah/kg (active material alone) or 900 Ah/kg (calculated with respect to the total mass: material + carbon black) or 4230 Ah/l (active material alone), more than 5.5 times the volumic capacity of graphite. The cycling behavior at fast rate ( C /6) was very good with a peculiar increase in capacity with cycle number after an initial decrease. Characterization of lithiated Li x NiVO 4 samples, performed with the use of local techniques such as X-ray absorption spectra (XAS) and electron energy loss spectroscopy (EELS), led to an evaluation of the average oxidation states of V and Ni and of the electronic transfer from Li to V and Ni. Results are compatible with the crystal chemistry of Ni and V oxides. The Li ‘incorporation/extraction’ process in the series Li x MVO 4 is not a destruction/reconstruction mechanism involving Li 2 O and M and V metals. However, it seems to be different from a classical topotactic intercalation reaction.

Structure cristalline du phosphatoantimonate K3Sb3P2O14

Abstract K3Sb3P2O14 crystallizes in the rhombohedral system, space group R 3 m with a = 7.147(1) A, c = 30.936(6) A, Z = 3. The structure was determined from 701 reflections collected on a Nonius CAD4 automatic diffractometer with Mo K α radiation. The final R index and the weighted Rw index are 0.033 and 0.042, respectively. The structure is built up from layers of SbO6 octahedra and PO4 tetrahedra sharing corners. The potassium ions are situated between the (Sb3P2O14)3− covalent layers.

Characterization of perovskite systems derived from Ba2In2O5□: Part I: the oxygen-deficient Ba2In2(1-x)Ti2xO5+x□1-x (0≤x≤1) compounds

Ba2In2(1−x)Ti2xO5+x□1−x (0≤x≤1) compounds have been prepared by solid state reaction. At room temperature (RT), when x increases, the progressive filling of oxygen vacancies, concomitant with the substitution of Ti for In, first induces (for 0<x≤0.075) a disorder in the plane of oxygen vacancies observed in Ba2In2O5□. Then, it suppresses the distortion to orthorhombic symmetry; for 0.075<x≤ 0.15, the symmetry becomes tetragonal and a formation of domains is observed. For 0.15<x<1, all members adopt a disordered cubic perovskite (DCP) structure at RT. Conductivity measurements between 450 and 800 °C show that the change from brownmillerite to tetragonal structure when x increases from 0.075 to 0.1 induces a drastic decrease of the activation energy. The highest oxide-ion conductivity is observed for 0.1≤x≤0.33: ∼0.5×10−2 S cm−1 at 700 °C.

Crystal structure of KSbP2O8

Abstract KSbP 2 O 8 crystallizes in the rhombohedral system, space group R 3 , with a = 4.7623(4) A, c = 25.409(4)A, and Z = 3. The structure was determined from 487 reflexions collected on a NONIUS CAD4 automatic diffractometer with Mo K − α radiation. The final R index and weighted R w index are 0.030 and 0.038, respectively. This structure is built up from layers of SbO 6 octahedra and PO 4 tetrahedra sharing corners. These (SbP 2 O − 8 ) n layers are very similar to the (ZrP 2 O 2− 8 ) n layers in the well-known α-ZrP compound.

Synthesis, structure and lithium-ion conductivity of Li2−2xMg2+x(MoO4)3 and Li3M(MoO4)3(MIII= Cr, Fe)

Lithium magnesium molybdates of the general formula Li2−2xMg2+x(MoO4)3, for 0 ≤ x ≤ 0.3, have been synthesized and their structure and lithium ion conductivity investigated. Determination of crystal structure of one of the members, Li2Mg2(MoO4)3, has revealed a three-dimensional framework consisting of metal–oxygen octahedra and trigonal prisms (where Li and Mg reside) which are interconnected by MoO4 tetrahedra. Although the framework is three-dimensional, lithium-ion conductivity appears to be restricted to the one-dimensional channels formed by interconnected trigonal prisms. Isotypic molybdates, Li3M(MoO4)3 (M = Cr, Fe), where lithium ions occupy exclusively the trigonal prismatic channels, exhibit a higher lithium ion conductivity than Li2−2xMg2+x(MoO4)3, lending support to the idea that the conductivity is one-dimensional in these materials. 7Li NMR spectral data are consistent with this interpretation.

Relative humidity influence on the water content and on the protonic conductivity of the phosphatoantimonic acids HnSbnP2O3n+5, xH2O (n = 1, 3, 5)

The phosphatoantimonic acids HnSbnP2O3n+5, xH2O (n = 1, 3, 5) have been prepared from the corresponding potassium compounds by ion-exchange in acidic medium. For n = 1 and 3 they are layered materials. When n = 5 the covalent framework is three dimensional with large interconnected channels. The title acids are all hydrated and their water content, lattice parameters and protonic conductivity have been studied at 20°C as a function of the relative humidity. When n = 1 a great part of the water content is physisorbed and the electrical behavior is that of a particle hydrate. For n = 3, the compound is a true lattice hydrate and the protonic conductivity is closely related to the water content. This is also the case when n = 5; however the contribution of surface water to the proton diffusion is clearly evidenced.

Characterization of perovskite systems derived from Ba2In2O5□: Part II: The proton compounds Ba2In2(1−x)Ti2xO4+2x(OH)y [0≤x≤1; y≤2(1−x)]

Abstract The proton compounds Ba 2 In 2(1− x ) Ti 2 x O 4+2 x (OH) y [0≤ x ≤1; y ≤2(1− x )] were prepared by reacting Ba 2 In 2(1− x ) Ti 2 x O 5+ x □ 1− x (0≤ x ≤1) phases with water vapor at ∼200 °C. For 0≤ x ≤0.20, the filling of oxygen vacancies is almost complete. For larger x values, it decreases significantly down to ∼30% only for x =0.7. The crystal structure of the end member Ba 2 In 2 O 4 (OH) 2 ( x =0) was reinvestigated by a combination of techniques including 1 H and 2 D NMR and electron, X-ray and neutron diffraction. The actual cell is eight times larger than that previously published. The structure analysis confirms that the sheet consisting of parallel chains of In(2)O 4 tetrahedra and parallel rows of oxygen vacancies in the parent structure of Ba 2 In 2 O 5 □ has been converted into a In(2)O 6 octahedral perovskite-like sheet. It demonstrates that the protons are bonded only to the O atoms around this In(2) site. When x increases, the change in reduced perovskite cell volume, concomitant with the water uptake, remains small for x x values. The proton conductivity was measured between room temperature and 180 °C. The highest conductivity at 180 °C, σ 180 ≈10 −6 S cm −1 , is observed for x ∼0.3.

Influence of the Cr Content on the Li Deinsertion Behavior of the LiCr y Mn2 − y O 4 ( 0 ⩽ y ⩽ 1 ) Compounds: I. Separation of Bulk and Superficial Processes at High Voltage

After a first charge-discharge cycle within the 4.3-5.2 V range, leading to the formation of a passivation layer, Li x Cr y Mn 2-y O 4 materials with y ≤ 0.75 present a good reversiblity contrary to those with y > 0.75. The use of a LiPF 6 -based, rather than a LiClO 4 -based electrolytes enables an easier separation of successive Li deinsertion processes, and strongly decreases the current of electrolyte oxidation above 5.1 V. However, regardless of the electrolyte, the separation of bulk and superficial phenomena on the active material can be done using methods which depend on the evolution of the electrolyte oxidation rate with the voltage. Thanks to these separation methods, the influence of various experimental parameters on the irreversible and cyclable capacities was examined. It is shown that the cyclable capacity does not depend on the scan rate provided that the end-of-charge voltage is high enough to reach the end of the deintercalation process. Furthermore, an optimized composition of the composite electrode is suggested from the variations of both capacities with the mass of active material and the carbon black content.