Showing papers by "Dany Carlier published in 2003"

A Combined Computational/Experimental Study on LiNi1/3Co1/3Mn1/3O2

Abstract: A combined computational/experimental study on LiNi1/3Co1/3Mn1/3O2 is presented. Both density functional theory and experiments are used to probe the active redox pairs and changes in electronic structure of LiNi1/3Co1/3Mn1/3O2 during intercalation or deintercalation of Li. The phase stability and voltage curve of this material are also shown in this paper. Both the experimental and computational data show that LiNi1/3Co1/3Mn1/3O2 material is a high-capacity stable electrode for advanced rechargeable lithium ion batteries.

Understanding the NMR shifts in paramagnetic transition metal oxides using density functional theory calculations

Abstract: The ${}^{6,7}\mathrm{Li}$ MAS NMR spectra of lithium ions in paramagnetic host materials are extremely sensitive to number and nature of the paramagnetic cations in the Li local environments and large shifts (Fermi contact shifts) are often observed. The work presented in this paper aims to provide a rational basis for the interpretation of the ${}^{6,7}\mathrm{Li}$ NMR shifts, as a function of the lithium local environment and electronic configuration of the transition metal ions. We focus on the layered rocksalts often found for ${\mathrm{LiMO}}_{2}$ compounds and on materials that are isostructural with the ${\mathrm{K}}_{2}{\mathrm{NiF}}_{4}$ structure. In order to understand the spin-density transfer mechanism from the transition metal ion to the lithium nucleus, which gives rise to the hyperfine shifts observed by NMR, we have performed density functional theory (DFT) calculations in the generalized gradient approximation. For each compound, we calculate the spin densities values on the transition metal, oxygen and lithium ions and map the spin density in the M-O-Li plane. Predictions of the calculations are in good agreement with several experimental results. We show that DFT calculations are a useful tool with which to interpret the observed paramagnetic shifts in layered oxides and to understand the major spin-density transfer processes. This information should help us to predict the magnitudes and signs of the Li hyperfine shifts for different Li local environments and ${t}_{2g}$ vs ${e}_{g}$ electrons in other compounds.

First-Principles Investigation of Phase Stability in the O2-LiCoO2 System

Abstract: A first-principles investigation of the phase stability in the O2-LiCoO2 system is performed to better understand the unusual layered phases obtained upon Li deintercalation (i.e., T#2 and O6). Fir...

Synthesis and electrochemical properties of layered Li0.9Ni0.45Ti0.55O2

Abstract: New Li0.9Ni0.45Ti0.55O2 positive electrode materials were synthesized by means of ion exchange from Na0.9Ni0.45Ti0.55O2. Powder X-ray diffraction (XRD) patterns for these materials indicate that they are isostructural with α-NaFeO2. The degree of cation disordering in the material depends critically on the synthesis conditions. Higher temperatures and longer ion-exchange times induce more cation disordering. Surprisingly, the partially disordered phase shows better capacity retention than the least disordered phase. First-principles calculations indicated the poor capacity retention in the least disordered phase could be attributed to the migration of Ti4+ into the Li layer during the electrochemical testing. The Ti4+ migration seems to depend sensitively on the Ni2+−Ti4+ configuration in the transition metal layer. Density of states (DOS) obtained from first-principles calculations indicate that only Ni participates in the electronic conductivity and that the poor conductivity of this material could be a...

A Combined Computational/Experimental Study on

Abstract: A combined computational/experimental study on LiNi1/3Co1/3Mn1/3O2 is presented. Both density functional theory and experiments are used to probe the active redox pairs and changes in electronic structure of LiNi1/3Co1/3Mn1/3O2 during intercalation or deintercalation of Li. The phase stability and voltage curve of this material are also shown in this paper. Both the experimental and computational data show that LiNi1/3Co1/3Mn1/3O2 material is a high-capacity stable electrode for advanced rechargeable lithium ion batteries.

Lithium and Vacancy Ordering in T#2−LixCoO2 Derived from O2-Type LiCoO2

Abstract: Electron diffraction revealed evidence of commensurate and incommensurate superstructures in an unusual phase, T#2, derived from O2-type layered LiCoO2 upon lithium deintercalation. 2aorth. × 2borth. × 2corth., 2aorth. × borth. × corth., and incommensurate with q = (γ = 0.23 and 0.36) superstructures were found. It is believed that lithium and vacancy ordering is the most probable cause for the presence of these superstructures. Lithium ordering configurations were discussed in detail with respect to the superstructures observed. It is believed that the presence of various lithium and vacancy ordering configurations improves the stability of the T#2 structure over a range of lithium compositions. Nevertheless, it should be mentioned that the nature of superstructures present and possible lithium ordering configurations in T#2−LixCoO2 were complex and further investigations are needed. In addition, it is of significance to point out that a combination of transmission electron microscopy and electron diffra...