In this study, a comprehensive experimental in situ analysis of the evolution of the occupied and unoccupied density of states as a function of the charging state of the Lix <= 1CoO2 films has been done by using synchrotron X-ray photoelectron spectroscopy (SXPS), X-ray photoelectron spectroscopy ()CPS), ultraviolet photoelectron spectroscopy (UPS), and 0 K- and Co L-3,L-2-edges XANES. Our experimental data demonstrate the change of the Fermi level position and the Co3d-02p hybridization under the Li+ removal and provide the evidence for the involvement of the oxygen states in the charge compensation. Thus, the rigid band model fails to describe the observed changes of the electronic structure. The Co site is involved in a Co3+ -> Co4+ oxidation at the period of the Li deintercalation (x similar to 0.5), while the electronic configuration at the oxygen site is stable up to 4.2 V. Further lowering of the Fermi level promoted by Li + extraction leads to a deviation of the electronic density of states due to structural distortions, and the top of the 02p bands overlaps the Co3d state which is accompanied by a hole transfer to the 02p states. The intrinsic voltage limit of LiCoO2 has been determined, and the energy band diagram of Lix <= 1CoO2 vs the evolution of the Fermi level has been built. It was concluded that LixCoO(2) cannot be stabilized at the deep Li deintercalation even with chemically compatible solid electrolytes.

The electronic properties of the LiMO2 (M = Ni, Co) thin film cathode materials grown by RF sputtering/co-sputtering are in situ studied by X-ray photoelectron spectroscopy (XPS). Stoichiometric Li1.0Co1.0O2 thin films deposited on a heated substrate at T = 500-550 degrees C reveal the Co3+ (t(2g)(6)e(g)(0)) ground state configuration in the low spin (LS) state. Stoichiometry of the Li-x(Ni,Co)O-2 films and the valence and spin states of the Ni ions depend strongly on the growth conditions. The electronic configuration of stoichiometric Li1.0Ni0.5Co0.5O2 is described as the Ni3+ (t(2g)(6)e(g)(1)) LS and Co3+ (t(2g)(6)e(g)(0)) LS states. The Li-deficient Li-x<1.0(Ni,Co)O-2 exhibits Ni2+ (t(2g)(6)e(g)(2)) in the high spin (HS) and Co3+ (t(2g)(6)e(g)(0)) in LS states. The reduction of the trivalent Ni ions to Ni2+ (t(2g)(6)e(g2)) with a HS state electronic configuration is related to the evaporation of Li2O at elevated substrate temperatures coupled to a loss of O-2 due to an internal oxidation reaction of O2- lattice ions induced by the strongly oxidizing Ni3+ ions. Owing to the stable Co3+ (t(2g)(6)e(g)(0)) with a LS state electronic configuration, Li1.0Co1.0O2 thin films cycled to 4.2 V exhibit a very good electrochemical reversibility. Li1.0Ni0.5Co0.5O2 films annealed at the same temperature as for Li1.0Co1.0O2 manifest a broadening of the oxidation/reduction peaks of the cyclic voltammogram (CV) curves with a strong current drop after the first step of the electrochemical Li-deintercalation. The observed irreversibility of the Li-intercalation/deintercalation process is attributed to instability of the Ni3+ (t(2g)(6)e(g)(1)) ions. Temperatures of the deposition/annealing above 750 degrees C lead to the phase separation of the Li-x(Ni,Co)O-2 films, a strong Li deficiency, the occurrence of Co2+ (t(2g)(5)e(g)(2)) with HS ions and consequently a complete degeneration of the electrochemical cyclability.

Three different experimental routes to in situ characterization of electronic structure and chemical composition of thin film cathode surfaces used in lithium ion batteries are presented. The focus is laid on changes in electronic structure and chemical composition during lithium intercalation and deintercalation studied by photoelectron spectroscopy and related techniques. At first, results are shown obtained from spontaneous intercalation into amorphous or polycrystalline V2O5 thin films after lithium deposition. Although this technique is simple and clean, it is nonreversible and only applicable to the first lithium intercalation cycle into the cathode only to be applied to host materials stable in the delithiated stage. For other cathode materials, as LiCoO2, a real electrochemical setup has to be used. In our second approach, the experiments are performed in a specially designed electrochemical cell directly connected to the vacuum system. First experimental results of RF magnetron sputtered V2O5 and LiCoO2 thin film cathodes are presented. In the third approach, an all solid-state microbattery cell must be prepared inside the vacuum chamber, which allows electrochemical processing and characterization by photoelectron spectroscopy in real time. We will present our status and experimental difficulties in preparing such cells.

Carbon Nano Fibers (CNFs) coated with LiFePO4 particles have been prepared by a non-aqueous sol–gel technique. The functionalization of the CNFs by HNO3 acid treatment has been confirmed by Raman and XPS analyses. The samples pure LiFePO4 and LiFePO4–CNF have been characterized by XRD, SEM, RAMAN, XPS and electrochemical analysis. The LiFePO4–CNF sample shows better electrochemical performance compared to as-prepared LiFePO4. LiFePO4–CNF (10wt.%) delivers a higher specific capacity (∼140mAhg−1) than LiFePO4 with carbon black (25wt.%) added after synthesis (∼120mAhg−1) at 0.1C.

Performance degradation of functional oxide materials and interfaces is – besides structural changes – caused by changes of the chemical composition, the electronic structure and the surface and interface potentials. In‐situ preparation and analysis for LiCoO2 thin films and for ITO/ZnPc interfaces are presented in this work. Sample stoichiometries, electronic structure and surface and interface potentials with photoelectron spectroscopy are analysed under well defined conditions.

The in situ chemical reaction of NiCo2O4 with Li and Na by physical vapor deposition is studied by using high-resolution X-ray photoelectron spectroscopy. The thermal decomposition of the mixed oxalate precursors at 320 °C allows the formation of NiCo2O4 as nanosized domains. The small particle size facilitates the reaction with Li and Na. During the first steps of the reaction of NiCo2O4 with both alkali metals, the reduction of both Ni3+ and Co3+ to the divalent state is demonstrated by XP spectroscopic data. The mechanism of the first steps of the reaction has been unfolded. A first intercalation reaction of the alkali ions in the spinel host structure occurs. In a second step, sodium oxide or lithium oxide is formed, as well as the monoxides.

Synchrotron-induced photoelectron spectroscopy was used to investigate the native-oxide-covered GaAs(100) surface and changes induced by etching with aqueous ammonia solution and by annealing in vacuum. The etching step removes arsenic and gallium oxides from the surface and the surface gets covered by elemental arsenic and tiny amounts of gallium suboxide. The surface oxygen content is reduced by an order of magnitude after etching, whereas the surface carbon content is somewhat increased. Annealing of this surface at 450°C results in the disappearance of elemental arsenic and a considerable decrease in surface carbon and oxygen contents. The valence band spectra exhibit clear features typical for As-terminated GaAs(100) surfaces, as also obtained after As decapping.

Preparation steps of Pt/n-GaAs Schottky contacts as applied in the fabrication process of varactor diode arrays for THz applications are analysed by photoelectron spectroscopy. Pulsed cathodic deposition of Pt onto GaAs (100) wafer surfaces from acidic solution has been studied by core level photoelectron spectroscopy using different excitation energies. A laboratory AlKα source as well as synchrotron radiation of hν=130 and 645 eV at BESSY was used. Chemical analyses and semiquantitative estimates of layer thickness are given for the natural oxide of an untreated wafer surface, a surface conditioning NH3 etching step, and stepwise pulse plating of Pt. The structural arrangement of the detected species and interface potentials are considered.