Nicolas Emery

The peculiar structural behaviour of β-Na0.33V2O5 upon electrochemical lithium insertion

The structural behaviour of the β-Na0.33V2O5 active material in a composite electrode is determined during discharge in the 3.8/2.2 V potential range (0 ≤ x < 1.66 in LixNa0.33V2O5) using X-ray diffraction combined with Raman microspectrometry. In spite of the existence of three well defined voltage plateaus, we provide evidence here for very weak structural changes throughout the lithium intercalation process, both at the long range order and local scale, involving mainly minor unit cell parameter variations. This result contrasts with the sharp phase transitions with one-phase and large two-phase regions usually observed for Li intercalation compounds exhibiting successive voltage plateaux separated by potential drops. The present findings demonstrate the reliability of a lithium filling scheme in the β-Na0.33V2O5 3D host lattice involving no phase transition in a remarkably wide Li composition range. Furthermore, new kinetic data for the electrochemical Li insertion reaction into β-Na0.33V2O5 are reported using AC impedance spectroscopy, which are discussed in relation with the specific structural response. This peculiar behaviour highlights the interest of such rigid tunnel framework to minimize the structural stress induced by lithium insertion.

A comparative insight of potassium vanadates as positive electrode materials for Li batteries: influence of the long-range and local structure.

Potassium vanadates with ratio K/V = 1:3, 1:4, and 1:8, prepared by a fast and facile synthesis route, were investigated as positive electrode materials in lithium batteries. KV3O8 and K0.5V2O5 have layered structures, while K0.25V2O5 exhibits a tunnel framework isomorphic to that of β-Na0.33V2O5. The Raman spectra of KV3O8, K0.5V2O5, and K0.25V2O5 compounds are reported here for the first time, and a detailed comparative analysis distinguishes spectral patterns specific to each structural arrangement. The electrochemical performances of these potassium vanadates toward lithium insertion were investigated. The potassium-richer compound KV3O8 shows a good rechargeability in spite of a low discharge capacity of 70 mAh g(-1), while the potassium-poorer bronze K0.25V2O5 exhibits the highest specific capacity of 230 mAh g(-1) but a slow and continuous capacity fade with cycling. We demonstrate that the K0.5V2O5 compound, with its double-sheet V2O5 layered framework characterized by a large interlayer spacing of 7.7 Å, is the best candidate as positive electrode for lithium battery among the potassium-vanadium bronzes and oxides. A remarkable specific capacity of 210 mAh g(-1), combined with excellent capacity retention, is achieved.

Phonon dispersion and low-energy anomaly in CaC6 from inelastic neutron and x-ray scattering experiments

We report measurements of phonon dispersion in CaC

Li2.0Ni0.67N, a Promising Negative Electrode Material for Li-Ion Batteries with a Soft Structural Response

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Electronic and magnetic properties of Nd1-xSrxMnAsO oxyarsenides

using inelastic X-ray and neutron scattering. We find good overall agreement, particularly in the 50 meV energy region, between experimental data and first-principles density-functional-theory calculations. However, on the longitudinal dispersion along the

Structural study and crystal chemistry of the first stage calcium graphite intercalation compound

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New kinetical and thermodynamical data concerning the intercalation of lithium and calcium into graphite

axis of the rhombohedral representation, we find an unexpected anti-crossing with an additional longitudinal mode, at about 11 meV. At a comparable energy, we observe also unexpected intensity on the in-plane direction. These results resolve the previous incorrect assignment of a longitudinal phonon mode to a transverse mode in the same energy range. By calculating the electron susceptibility from first principles we show that this longitudinal excitation is unlikely to be due to a plasmon and consequently can probably be due to defects or vacancies present in the sample.

K0.5V2O5: A novel Li intercalation compound as positive electrode material for rechargeable lithium batteries

The layered lithium nitridonickelate Li2.0(1)Ni0.67(2)N has been investigated as a negative electrode in the 0.02-1.25 V vs Li+/Li potential window. Its structural and electrochemical properties are reported. Operando XRD experiments upon three successive cycles clearly demonstrate a single-phase behavior in line with the discharge-charge profiles. The reversible breathing of the hexagonal structure, implying a supercell, is fully explained. The Ni2+/Ni+ redox couple is involved, and the electron transfer is combined with the reversible accommodation of Li+ ions in the cationic vacancies. The structural response is fully reversible and minimal, with a maximum volume variation of 2%. As a consequence, a high capacity of 200 mAh g-1 at C/10 is obtained with an excellent capacity retention, close to 100% even after 100 cycles, which makes Li2.0(1)Ni0.67(2)N a promising negative electrode material for Li-ion batteries.

Superconductivity in Li3Ca2C6 intercalated graphite

The oxypnictides Nd1-xSrxMnAsO have been successfully synthesised with x up to 0.1. A synchrotron X-ray diffraction study demonstrates that there is no change in crystal symmetry upon doping with Sr. An expansion of the inter-layer distance between Nd-O-Nd and As-Mn-As blocks is observed with increasing x. Results from variable temperature neutron diffraction and resistivity measurements show that the local moment antiferromagnetic order of the Mn spins is preserved as the [MnAs]- layers are hole doped and the materials are driven metallic for x > 0.05. A sizeable positive magnetoresistance is observed at low temperature which demonstrates that multiple MR mechanisms are possible in LnMnAsO oxypnictides.