Daria Mikhailova

XPS investigations of electrolyte/electrode interactions for various Li-ion battery materials

AbstractFor future Li-ion battery applications the search for both new design concepts and materials is necessary. The electrodes of the batteries are always in contact with electrolytes, which are responsible for the transport of Li ions during the charging and discharging process. A broad range of materials is considered for both electrolytes and electrodes so that very different chemical interactions between them can occur, while good cycling behavior can only be obtained for stable solid-electrolyte interfaces. X-ray photoelectron spectroscopy (XPS) was used to study the most relevant interactions between various electrode materials in contact with different electrolyte solutions. It is shown how XPS can provide useful information on reactivities and thus preselect suitable electrode/electrolyte combinations, prior to electrochemical performance tests. FigureCharacteristic changes of the Li1s XP-spectra at Li2O2 powder after storage in LiPF6 for various time point to a LiF formation

Magnetism and spin-orbit coupling in Ir-based double perovskites La_{2−x}Sr_{x}CoIrO_{6}

We have studied Ir spin and orbital magnetic moments in the double perovskites La2−xSrxCoIrO6 by x-ray magnetic circular dichroism. In La2CoIrO6, Ir4+ couples antiferromagnetically to the weak ferromagnetic moment of the canted Co2+ sublattice and shows an unusually large negative total magnetic moment (−0.38 μB/f.u.) combined with strong spin-orbit interaction. In contrast, in Sr2CoIrO6, Ir5+ has a paramagnetic moment with almost no orbital contribution. A simple kinetic-energy-driven mechanism including spin-orbit coupling explains why Ir is susceptible to the induction of substantial magnetic moments in the double perovskite structure.

The role of oxygen stoichiometry on phase stability, structure, and magnetic properties of Sr2CoIrO(6-δ).

The phase stability, crystal structure, and magnetic properties of perovskite-like nonstoichiometric Sr(2)CoIrO(6-δ) were studied. Oxygen deficiency can be well controlled and reversibly varied up to δ = 0.33. A single phase exists at least for partial oxygen pressures between 10(-5) and 1 bar at 1273 K, followed by phase decomposition at higher temperature with the elimination of metallic Ir and the formation of a new phase with approximately Sr(3)CoIrO(6) composition crystallizing in K(4)CdCl(6) structure type. The structural features of Sr(2)CoIrO(6-δ) are dependent on both temperature and oxygen content and were determined by synchrotron and neutron powder diffraction. Both the increasing amount of oxygen vacancies at constant temperature and increasing temperature at constant oxygen content result in the same higher crystal symmetry of Sr(2)CoIrO(6-δ): (1) The oxygen-stoichiometric phase Sr(2)CoIrO(6.00) is monoclinic (I2/m or P2(1)/n) at room temperature but cubic (Fm-3m) for Sr(2)CoIrO(5.67). (2) A sequence of phase transitions [Formula: see text] was observed for Sr(2)CoIrO(6.00) in air. All Sr(2)CoIrO(6-δ) compositions show weak ferromagnetism at low temperature with a canted but predominantly antiferromagnetic ground state. The magnetic ordering temperature decreases monotonously with increasing oxygen deficiency, while pronounced extrema are observed for the paramagnetic moment and the Curie-Weiss temperature at an oxygen deficiency δ ≈ 0.10, which corresponds to the P2(1)/n ↔ I2/m phase transformation.

Phase transitions in jalpaite, Ag3CuS2

Ag3CuS2 is comprehensively studied by applying synchrotron and neutron powder diffraction as well as thermal analysis in the range from 2 K up to the melting point around 960 K. The unique sequence of the reversible phase transitions P- was detected prior to the samples melting. The transitions at 110, 387 and 483–549 K are found to be of first order, whereas the transition at 250 K is a second-order one. The major change in the structure of jalpaite resulting from the phase transition is a modification in the coordination geometry of the silver atoms. A large degree of structural disorder is stated for - and -structured Ag3CuS2, which correlates with the high ionic conductivity within both cubic polymorphs. The thermal expansion of jalpaite shows some unusual features, i.e. a negative expansion along the c-direction in the I41/amd phase, a nonlinear expansion within the polymorph and an expansion increase upon entering the mixed region. Low-temperature specific heat data confirm first- and second-order anomalies at 110 and 250 K, respectively, and illustrate a pronounced non-Debye-like behaviour of jalpaite.

Thermal stability of Li1−ΔM0.5Mn1.5O4 (M = Fe, Co, Ni) cathodes in different states of delithiation Δ

The thermal stability of sol–gel synthesized Li1−ΔM0.5Mn1.5O4 (M = Fe, Co, Ni) electrodes with different degrees of delithiation were analyzed with TG-DSC and in situ synchrotron diffraction under an Ar atmosphere and compared. The onset temperatures for structural degradation are dependent on the amount of lithium 1−Δ in the sample. The Li1−ΔFe0.5Mn1.5O4 electrode exhibited the highest thermal stability among the three materials with different dopant M. The reason for this difference is discussed with respect to the oxidation states of the transition metals. The mechanism of degradation for M = Fe, Co was found to be through gas evolution, mainly CO2 and O2, and the carbon conductive additive was found to play a major role in the thermal degradation process. For delithiated Li1−ΔNi0.5Mn1.5O4 the temperature induced degradation includes phase separation into Mn3O4 with spinel structure and LixNi1−xO with rock-salt structure together with oxygen and carbon dioxide release.

Layered-to-Tunnel Structure Transformation and Oxygen Redox Chemistry in LiRhO2 upon Li Extraction and Insertion

Layered Li(M,Li)O2 (where M is a transition metal) ordered rock-salt-type structures are used in advanced metal-ion batteries as one of the best hosts for the reversible intercalation of Li ions. Besides the conventional redox reaction involving oxidation/reduction of the M cation upon Li extraction/insertion, creating oxygen-located holes because of the partial oxygen oxidation increases capacity while maintaining the oxidized oxygen species in the lattice through high covalency of the M-O bonding. Typical degradation mechanism of the Li(M,Li)O2 electrodes involves partially irreversible M cation migration toward the Li positions, resulting in gradual capacity/voltage fade. Here, using LiRhO2 as a model system (isostructural and isoelectronic to LiCoO2), for the first time, we demonstrate an intimate coupling between the oxygen redox and M cation migration. A formation of the oxidized oxygen species upon electrochemical Li extraction coincides with transformation of the layered Li1-xRhO2 structure into the γ-MnO2-type rutile-ramsdellite intergrowth LiyRh3O6 structure with rutile-like [1 × 1] channels along with bigger ramsdellite-like [2 × 1] tunnels through massive and concerted Rh migration toward the empty positions in the Li layers. The oxidized oxygen dimers with the O-O distances as short as 2.26 Å are stabilized in this structure via the local Rh-O configuration reminiscent to that in the μ-peroxo-μ-hydroxo Rh complexes. The LiyRh3O6 structure is remarkably stable upon electrochemical cycling illustrating that proper structural implementation of the oxidized oxygen species can open a pathway toward deliberate employment of the anion redox chemistry in high-capacity/high-voltage positive electrodes for metal-ion batteries.

Coordination of the Mn4+-Center in Layered Li[Co0.98Mn0.02]O2 Cathode Materials for Lithium-Ion Batteries

Abstract The local coordination of the manganese in Li[Co0.98Mn0.02]O2 cathode materials for lithium-ion batteries has been investigated by means of a joint XRD and multi-frequency electron paramagnetic resonance (EPR) characterization approach. EPR showed the manganese being in a tetravalent high-spin Mn4+-oxidation state with S=32.

New lithium copper borates with BO3 triangles: Li6CuB4O10, Li3CuB3O7, Li8Cu7B14O32, and Li2Cu9B12O28.

S = {3 \over 2}.

Synthesis and crystal structure of a new rhenium scandium oxide, Sc 6 ReO 12

The set of spin-Hamiltonian parameters obtained from the multi-frequency EPR analysis with Larmor frequencies ranging between 9.4 and 406 GHz is transformed into structural information by means of the recently introduced Monte-Carlo Newman-superposition modeling. Based on this analysis, the Mn4+ are shown being incorporated for the Co3+-sites, i.e. acting as donor-type functional centers MnCo•

Intricacies of the Co3+ spin state in Sr2Co0.5Ir0.5O4: An x-ray absorption and magnetic circular dichroism study

{\rm{Mn}}_{{\rm{Co}}}^ \bullet