Laurent Duda

Charge-compensation in 3d-transition-metal-oxide intercalation cathodes through the generation of localized electron holes on oxygen

During the charging and discharging of lithium-ion-battery cathodes through the de- and reintercalation of lithium ions, electroneutrality is maintained by transition-metal redox chemistry, which limits the charge that can be stored. However, for some transition-metal oxides this limit can be broken and oxygen loss and/or oxygen redox reactions have been proposed to explain the phenomenon. We present operando mass spectrometry of (18)O-labelled Li1.2[Ni0.13(2+)Co0.13(3+)Mn0.54(4+)]O2, which demonstrates that oxygen is extracted from the lattice on charging a Li1.2[Ni0.13(2+)Co0.13(3+)Mn0.54(4+)]O2 cathode, although we detected no O2 evolution. Combined soft X-ray absorption spectroscopy, resonant inelastic X-ray scattering spectroscopy, X-ray absorption near edge structure spectroscopy and Raman spectroscopy demonstrates that, in addition to oxygen loss, Li(+) removal is charge compensated by the formation of localized electron holes on O atoms coordinated by Mn(4+) and Li(+) ions, which serve to promote the localization, and not the formation, of true O2(2-) (peroxide, O-O ~1.45 Å) species. The quantity of charge compensated by oxygen removal and by the formation of electron holes on the O atoms is estimated, and for the case described here the latter dominates.

Anion Redox Chemistry in the Cobalt Free 3d Transition Metal Oxide Intercalation Electrode Li[Li0.2Ni0.2Mn0.6]O2

Conventional intercalation cathodes for lithium batteries store charge in redox reactions associated with the transition metal cations, e.g., Mn(3+/4+) in LiMn2O4, and this limits the energy storage of Li-ion batteries. Compounds such as Li[Li0.2Ni0.2Mn0.6]O2 exhibit a capacity to store charge in excess of the transition metal redox reactions. The additional capacity occurs at and above 4.5 V versus Li(+)/Li. The capacity at 4.5 V is dominated by oxidation of the O(2-) anions accounting for ∼0.43 e(-)/formula unit, with an additional 0.06 e(-)/formula unit being associated with O loss from the lattice. In contrast, the capacity above 4.5 V is mainly O loss, ∼0.08 e(-)/formula. The O redox reaction involves the formation of localized hole states on O during charge, which are located on O coordinated by (Mn(4+)/Li(+)). The results have been obtained by combining operando electrochemical mass spec on (18)O labeled Li[Li0.2Ni0.2Mn0.6]O2 with XANES, soft X-ray spectroscopy, resonant inelastic X-ray spectroscopy, and Raman spectroscopy. Finally the general features of O redox are described with discussion about the role of comparatively ionic (less covalent) 3d metal-oxygen interaction on anion redox in lithium rich cathode materials.

Local Electronic Structure of Functional Groups in Glycine As Anion, Zwitterion, and Cation in Aqueous Solution

Nitrogen and oxygen K emission spectra of glycine in the form of anions, zwitterions, and cations in aqueous solution are presented. It is shown that protonation has a dramatic influence on the local electronic structure and that the functional groups give a distinct spectral fingerprint.

Symmetry Selection in Polarized Resonant X-Ray Emission Spectroscopy in La2CuO4.

Experimental and theoretical investigations are made for the polarization dependence in the resonant X-ray emission spectra due to the Cu 3 d →2 p electronic transition under the Cu 2 p →3 d resonant excitation (Cu 2 p -RXES) in La 2 CuO 4 . It is shown that the polarization dependence of the Cu 2 p -RXES can be deduced from the spectra obtained under the various geometrical configurations of the crystal axis, the polarization direction of the incident beam, and the direction of the detector. The calculated results are in fairly good agreement with the experimental results.

End station for polarization and excitation energy selective soft x‐ray fluorescence spectroscopy

An end station for soft x‐ray fluorescence spectroscopy has been constructed, which includes an experiment chamber, rotatable 90° under ultrahigh vacuum conditions around the incoming synchrotron radiation beam, which is provided with a high‐resolution soft x‐ray spectrometer. A manipulator allowing three axes of rotation, three directions of translation, as well as LN2 cooling and resistive heating is mounted to the chamber and serves as the sample holder. Samples can be transferred under vacuum between the experiment chamber and two other chambers, one for sample preparation and another for introducing new samples and for sample storage. The end station has been used at two different synchrotron radiation laboratories (beamline BW3) at HASYLAB in Hamburg and at ALS (beamline 7.0) in Berkeley. Polarization‐dependent and angular resolved, selectively excited x‐ray emission studies have been made on ordered as well as nonordered systems, e.g., high‐Tc superconducting systems, diamond, fullerenes, and molec...

Resonant Soft X-Ray Emission Spectroscopy and X-Ray Absorption Spectroscopy on the Cathode Material LiNi0.65Co0.25Mn0.1O2

The topic of this thesis is redox reactions in two technologically important contexts: firstly, in Li-ion battery electrodes during cycling, and secondly, in copper corrosion in oxygen-free ground water containing sulfide. In an attempt to expand the understanding of the charge uptake process in battery electrodes and the chemical reactions on copper surfaces upon sulfide exposure, soft X-ray spectroscopy has been used to study the electronic structure of these systems. To ascertain the changes in electron density at different atomic sites in a battery electrode material, both X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) have been applied to different electrode materials. This thesis explains in detail the assembling procedure, cycling, and situ sample preparation of the battery materials. Furthermore, two different designs used in in situ experiments for study of batteries during cycling are also discussed. The main result from the Li-ion battery materials is the justification to abandon the view of valences as integers. This is true for all battery electrodes examined in this thesis. Generally, oxygen plays a more important role in the charge uptake than commonly assumed, but also the transition metals and other species apart from expected behavior. In LiMnPO4, even the notion of Li as strictly Li+ must be questioned. Copper is intended to act as a corrosion barrier in a nuclear waste repository. In the corrosion experiments presented in this thesis, different copper oxides were exposed to the conditions present at the planned repository site, with exception for the concentration of sulfide, which was greatly increased. The conclusion from these experiments is that sulfide effectively reduces Cu(II) oxide to Cu(I) compounds and possibly forms a compound containing both oxygen and sulfur. Also, the thickness and inhomogeneity of the copper oxide surface layers are of great importance for the corrosion mechanisms, including passivation.

Electronic structure of water molecules confined in a micelle lattice

Oxygen K absorption and emission spectra of water molecules confined in dodecyltrimethyl ammonium chloride micelle structures are presented. The local electronic structure of the water molecules is found to be dramatically different from the electronic structure of water molecules in the gas-phase as well as in liquid water. Hybridization with states of the ions in the surrounding ions is directly observed, and evidence for stabilization of the water molecules relative to molecules in bulk water is found.

The electronic structure and lithiation of electrodes based on vanadium-oxide nanotubes

The effect of lithium insertion (lithiation) in electrodes of vanadium oxide nanotubes has been studied using resonant soft-x-ray emission spectroscopy (RSXES) and soft x-ray absorption spectroscopy (SXAS). Spectra at the V L edges were recorded ex-situ on a series of cycled electrodes that had been discharged to different potentials (3.0, 2.5, 2.0, and 1.8 V). Different chemical states upon discharge effectively correspond to different doping levels: the lower the cell potential, the higher the lithiation. The RSXES and SXAS spectra reflect the occupied and unoccupied electronic states, respectively. Spectral changes are observed as a function of the reduction process of vanadium by the electrochemical process. Lithiation induces a gradual enhancement of features attributed to occupied V 3d states in the RSXES spectra, indicating that the intercalated charges occupy bands of V 3d. Both SXAS and RSXES results suggest a partial reduction to V3+ at potentials below 2.0 V and the presence of a mixture of thr...

Observation of multiple Zhang-Rice excitations in a correlated solid: Resonant inelastic X-ray scattering study of Li2CuO2

Multiple Zhang-Rice type spectral features have been observed in resonant inelastic X-ray scattering (RIXS) from the quasi–one-dimensional cuprate charge transfer insulator Li2CuO2. The first feature appears at constant emission energy, and is associated with a Zhang-Rice singlet final state. The second is an interplaquette charge transfer excitation that results in a novel triplet Zhang-Rice–type final state. It is accompanied by the presence of a O 2p nonbonding to upper Hubbard band excitation at an energy close to that of a calculated triplet charge transfer Zhang-Rice–type excitation. The site selectivity and polarization rules associated with RIXS allows these two excitations to be distinguished.

Direct observation of temperature-dependent Fermi surface nesting vectors in a quasi-one-dimensional conductor

We present the first direct observation of temperature-dependent Fermi wave vectors in the quasi-one-dimensional conductor K0.3 MoO3 . By monitoring the position of these vectors through the Peierls transition using angle-resolved photoemission spectroscopy, we demonstrate that the temperature dependence of the charge-density-wave vector observed in earlier experiments is actually that of the Fermi wave vectors.