Michel Ménétrier

The LixV2O5 system: An overview of the structure modifications induced by the lithium intercalation

Abstract Depending on the amount of lithium ( x ) intercalated in V 2 O 5 several structural modifications are observed. For the smallest lithium contents, the α −( x e −(0.35 x 2 O 5 type structure with an increasing puckering of the layers. For the LiV 2 O 5 composition, a gliding of one layer out of two leads to the δ-type structure. All these reactions are fully reversible and the pristine V 2 O 5 phase is recovered upon deintercalation. For intercalation amounts larger than one, the δ-phase is transformed into a γ-one via an irreversible reconstruction mechanism.the γ−Li x V 2 O 5 phase can itself be reversibly cycled in the 0.0≤ x ≤2.0 range while maintaining the γ-type structure. A new metastable variety of V 2 O 5 has been obtained. The intercalation of the third lithium atom in V 2 O 5 leads irreversibly to the formation of an ω-type phase that exhibits a rocksalt type structure. Almost all the lithium can be electrochemically or chemically removed from this material, leading to a unique positive electrode materials for secondary lithium batteries.

On the structure of Li3Ti2(PO4)3

The structure of the Nasicon-type phase Li3Ti2(PO4)3, obtained by chemical lithiation of LiTi2(PO4)3, has been characterised using neutron diffraction for the long range structure and 7Li NMR for more local information. The lithium atoms were precisely located from the neutron diffraction data, using nuclear difference Fourier maps. The lithium ions, which were known to be in the large M2 cavity, occupy two M3 and M′3 subsites (distorted tetrahedra) with occupation factors of 2/3 and 1/3, respectively. From these two intermediate sites, it was shown that the diffusion pathway between two M1 sites in these Nasicon-type structures consists of a set of seven face-sharing tetrahedra. A variable temperature 7Li MAS NMR study showed a set of signals due to a distribution of environments for a given Li+ ion, in terms of occupied or vacant M3/M′3 sites in its vicinity. Elevation of the temperature to 353 K leads to a reversible exchange of these signals, due to fast hopping of Li between the two sites within a given M2 cavity.

Electrochemical and structural characterization of lithium intercalation and deintercalation in the γ-LiV2O5 bronze

Abstract The γ-LiV2O5 bronze has a layer-like structure. Provided that x does not exceed 2, it can insert reversibly lithium without major structural rearrangement but with formation of a new ζ-phase for large x-values. Deintercalation of lithium from γ-LiV2O5 at oxidation potentials larger than 3.5 V leads to formation of a new orthorhombic γ-phase. Complete deintercalation is achieved at a potential of 3.65 V giving rise to a new form of vanadium pentoxide.

On the LixCo1−yMgyO2 system upon deintercalation: electrochemical, electronic properties and 7Li MAS NMR studies

A detailed characterization of the structural modifications and redox processes occurring upon lithium deintercalation from the Lix0Co1−yMgyO2 materials (x0=1.0 and 1.10; y=0.0, 0.03, 0.05 and 0.06) was performed in order to determine the effect of Mg doping on the cycling properties. Using electrochemical tests, X-ray diffraction (XRD), 7Li MAS NMR and electrical properties measurements, we show that the LixCo1−yMgyO2 system exhibits a solid solution existing in the whole deintercalation range studied (0.30≤×≤1.0). These phases exhibit reversible capacities equivalent to that of LiCoO2 upon cycling with a good structural stability. Moreover, the 7Li MAS NMR study shows that the structural defects (O vacancies and intermediate spin Co3+ ions) which are present in the starting Mg-doped phases govern the electronic properties upon lithium deintercalation. Indeed, regardless of the presence of Mg ions in the structure, a behavior similar to that of the LixCoO2 (1

Investigation of the Second Discharge Plateau of the β ( III ) ‐ NiOOH / β ( II ) ‐ Ni ( OH ) 2 System

The galvanostatic reduction of the nickel hydroxide electrode is known to proceed at two successive potentials without this phenomenon being well understood. In this paper the authors prove that this second discharge plateau is unrelated to oxygen reduction and that it can be observed in the absence of the {gamma}-NiOOH hydrated phase. Some earlier studies have connected it to the phase diagram of the {beta}(III)/{beta}(II) system. Using highly precise X-ray measurements, the authors demonstrate that the latter is quite different from the one commonly used. They then interpret the unusual shapes of potential relaxation curves during the lower discharge plateau. Measurements over a wide range of current density (four orders of magnitude) yield experimental clues for an original interpretation of the second discharge plateau based on the dynamics of the discharge process. They suggest that the second plateau is due to the existence of a phase close to Ni(OH){sub 2}, which is not ionically conductive but (poorly) electronically conductive, in the vicinity of the current collector.

Synthesis of Li1.1(Ni0.425Mn0.425Co0,15)0.9O1.8F0.2 Materials by Different Routes : Is There Fluorine Substitution for Oxygen?

A one-step synthesis method was used, with LiF or NiF 2 as fluorine precursor, to prepare Li 1.1 (Ni 0.425 Mn 0.425 Co 0.15 ) 0.9 O 1.8 F 0.2 materials. 7 Li and 19 F magic angle spinning NMR analyses revealed the presence of fluorine as LiF at the surface of the Li(Ni 0.425 Mn 0.425 Co 0.15 )O 2 particles, rejecting the formation of fluorine-substituted Li 1.1 (Ni 0.425 Mn 0.425 Co 0.15 ) 0.9 O 8 F 0.2 materials. These results highlighted that change in cell parameters with increasing fluorine content is not by itself proof for effective fluorine substitution for oxygen in layered oxides and that heterogeneity in the transition metal and fluoride-ion distribution at the crystallite scale can be at the origin of these modifications. LiF was shown to be present as small particles in some grain boundaries but not as a continuous layer covering the particles surface. Improved cycling stability was observed for these LiF-coated materials, showing that effective fluorine substitution for oxygen is not required for improvement of the cyclability of these layered oxides; a surface modification can be sufficient and can also have a huge impact.

Lithium Electrochemical Deintercalation from O 2 ­ LiCoO2 Structure and Physical Properties

Electrochemical deintercalation of Li from the metastable O2-LiCoO 2 phase has been investigated up to the composition Li 0.15 CoO 2 . The single-phase domains that separate the voltage plateaus observed have been characterized by X-ray diffraction. The succession of phases observed upon deintercalation results from reversible sheet gliding or lithium/vacancy ordering, leading to the sequence 02, T#2, T#2, 06, 02, 02. In particular, the T#2 stacking, similar to the T2 phase reported by Dahn and co-workers for the Li 2/3 Ni 1/3 Mn 2/3 O 2 phases, corresponds to oxygen ions not sitting on the three positions of a triangular lattice, hence the # character is used. It exhibits very distorted tetrahedral sites for Li. The 06 stacking exhibits two kinds of CoO 6 octahedra, which might allow Co 3+ /Co 4+ ordering in alternate sheets. The most deintercalated O2-Li 0.15 CoO 2 phase has never been reported before. Electronic properties and 7 Li magic-angle spinning nuclear magnetic resonance show a transition to a metallic state for x< 0.94 (appearance of the T#2 phase with x = 0.72). These stacking changes are proposed to result from the minimization of electrostatic repulsion, except for T#2 (x = 0.50), which is believed to result from a Li/vacancy ordering.

A brief overview on low sodium content silicides: are they mainly clathrates, fullerenes, intercalation compounds or Zintl phases?

Low sodium content silicides discovered by some of us in the sixties are compared to some analogous families of materials. As endofullerenes constituted by the smallest Si 20 ,S i 24 and Si28 clusters, they are polymerized in 3D-structures of face sharing polyhedra, giving rise to clathrate-like structures (similar to those of the gas and liquid hydrates). Several physical properties (conductivity, 23 Na and 29 Si NMR, EPR) show that the electronic transfer from sodium to the silicon host is rather low and appears only gradually with rising Na-content as a consequence of Na 3s and Si 3s-3p orbital mixing which gives rise to an antibonding band. Silicon clathrates differ from the homologous germanium and tin compounds characterized by a large number of defects in the host structure which leads to stronger ionization of the alkali atoms and to the formation of some Ge − anions within Zintl–Klemm-type phases. uf6d9 2002 Editions scientifiques et medicales

Elucidating the origins of phase transformation hysteresis during electrochemical cycling of Li–Sb electrodes

We investigate the origins of phase transformation hysteresis in electrodes of Li-ion batteries, focusing on the alloying reaction of Li with Sb. Electrochemical measurements confirm that the reaction path followed during Li insertion into Sb electrodes differs from that followed upon subsequent Li extraction. Results from first-principles calculations and NMR measurements indicate that Li3Sb is capable of tolerating high Li-vacancy concentrations. An unusually high Li mobility in Li3Sb facilitates over potentials during charging, which leads to a substantially larger driving force for the nucleation of Sb compared to that of Li2Sb. The differences in nucleation driving forces arise from a lever effect that favors phases with large changes in Li concentration over phases that are closer in composition along the equilibrium path. These properties provide an explanation for the observed path hysteresis between charge and discharge in the Li–Sb system and likely also play a role in intercalation compounds and other alloying reactions exhibiting similar phase transformation hysteresis.

New secondary batteries for room temperature applications using a vitreous electrolyte

Abstract In order to obtain room temperature high energy secondary batteries, a B 2 S 3 ue5f8Li 2 Sue5f8LiI vitreous electrolyte has been used. Lithium or a lithium-aluminium alloy have been tested as negative electrode in symmetrical cells and then utilized in four different types of experimental Li (or LiAl) /glass/TiS 2 batteries. The best results have been obtained with a composite TiS 2 -liquid electrolyte positive electrode.