The stability of the valence state of the 3d transition metal ions and the stoichiometry of LiMO(2) (M = Co, Ni, Mn) layered oxides at the surface-electrolyte interface plays a crucial role in energy storage applications. The surface oxidation/reduction of the cations caused by the contact of the solids to air or to the electrolyte results in the blocking of the Li-transport through the interface that leads to the fast batteries deterioration. The influence of the end-of-charge voltage on the chemical composition and the oxidation state of 3d transition metal ions, as well as the stability of the solid-electrolyte interface formed during the electrochemical Li-deintercalation/intercalation of the LiCoO(2) and Li(Ni,Mn,Co)O(2), have been investigated by X-ray photoelectron spectroscopy. While the chemical composition of the solid-electrolyte interface is similar for both layered oxide surfaces, the electrochemical cycling to some critical voltage values leads to the disappearance of the interface. By the analysis of the shape of the 2p and 3s photoelectron emissions we show that the formation of the solid-electrolyte interface layer correlates with the partial reduction of the trivalent Co ions at the electrolyte-LiCoO(2) interface and the amount of the Co(2+) ions is increased as the solid-electrolyte interface vanishes. In contrast, the Mn(4+), Co(3+) and Ni(2+) ions of the Li(Ni,Mn,Co)O(2) are stable at the interface under the electrochemical cycling to higher end-of-charge voltage. A correlation between deterioration of the LiCoO(2) and Li(Ni,Mn,Co)O(2) batteries and the change of electronic structure at the surface/interface after the electrochemical cycling has been found. The dissolution of the solid-electrolyte interface layer might be the reason for the fast deterioration of the Li-ion batteries.

In this contribution, we investigate the solid electrolyte interface (SEI) layers' composition depending on the spatial location within LiCoO 2 composite cathode of a commercial Li-Ion battery. The surface chemistry is analyzed by X-ray photoelectron spectroscopy (XPS), and possible SEI morphology and the differences in the SEI composition are discussed in detail. Finally, related SEI formation reactions and the controlling processes are characterized as a function of the depth in the composite cathode. The SEI is assumed to be a multi-component, layered system. The inorganic inner SEI layer consists of LiF and degraded LiCoO 2 , confirmed as Co(II,III) x O y (OH) z . The much thicker outer SEI layer is mainly composed of a poly-organic network with a significantly smaller portion of, presumably, randomly distributed macroscopic Li x PO y F z /Li x PO y-1 F z+1 and Li x PO y domains. A higher content of Co(II,III) x O y (OH) z , and especially of the poly-organic deposit, was found on the outer cathode surface compared to the analysis position near the current collector, resulting in a 4 nm thicker SEI and indicating a stronger decomposition of LiCoO 2 and solvents. These differences in SEI composition and thickness are attributed to a significantly higher cathode polarization at the outer electrode surface during cell operation leading to a higher rate of electrochemically induced decomposition reactions.

In this contribution, we investigate the initial surface chemistry on fully lithiated LiCoO 2 thin film model electrodes in the electrolyte solvent diethyl carbonate (DEC) and the LiPF 6 -electrolyte by means of soaking experiments. The interfacial layer composition is analyzed by X-ray photoelectron spectroscopy (XPS), and possible layer morphologies and spontaneous formation mechanisms are discussed in detail. Upon decomposition of DEC a layered system of surface-bound semi-organic components (inner layer) and cross-linked organic moieties (outer layer) is formed, while a change of the Co 3+ oxidation state and thus a surface corrosion of LiCoO 2 was not observed. In contrast, the solid electrolyte interface (SEI) film of the LiPF 6 -electrolyte soaked electrode showed an inner layer, containing predominantly corroded LiCoO 2 , i.e. Co(II,III) x O y (OH) z and LiF as well as aliphatic fluoroorganic species. The outer SEI layer consists mainly of a poly-organic network and randomly distributed Li x PO y F z domains. The thickness of the deposit on the electrolyte soaked electrode surface was only half as thick due to the significantly lower amount of organic and semi-organic compounds. Our investigation indicates that the solvent decomposition is related to the catalytically active LiCoO 2 surface, which is passivated by reaction products such as LiF originating from HF induced processes.

CH 3 NH 3 PbX 3 (X = Cl, Br, I) perovskites were prepared by self-organization processes using different precursor solutions. The XRD analysis indicates the formation, at room temperature, of a tetragonal structure (space group I 4/mcm) for X = I, of a cubic structure (space group Pm3m) for X = Br and of centro-symmetric cubic structure (space group Pm3m) for X = Cl respectively. The structural analysis revealed the formation of CH3NH3Cl as secondary phase in the Cl-containing system. The morphological investigation revealed the formation of rhombo-hexagonal dodecahedra crystallite for X = I, Br whereas cube-like aggregates were observed for X = Cl. The thermogravimetric analysis performed in air did not reveal any loss until 250°C for X = I and 300°C for X = Br respectively whereas the differential thermal analysis (DTA) detected two endothermic thermal events (at 336°C and 409°C) for X = I and one only (379°C) for X = Br respectively. The infrared spectra (IR) of the powders conformed to the threefold symmetry of the methylammonium ion which rotates around the C-N axis. Optical absorption measurements indicated that the CH 3 NH 3 PbX 3 systems behave as direct-gap semiconductors with energy band gaps of 1.53eV for X = I, 2.20eV for X = Br and 3.00eV for X = Cl respectively at room temperature. The direct-gap semiconductivity for X = I and X = Br was confirmed by the photoluminescence emission measurements whereas the compound for X = Cl is inactive. I-containing powders were dissolved in an organic solvent (di-methyl-formamide, DMF). 100 -300 µL of the dispersion were dropped on glassy substrates on which thick films were obtained by spin-coating and thermal treatment at 120°C for ca. 5 minutes. The preparation of the layers was performed in air at room temperature.

Nanostructured materials lie at the heart of fundamental advances in efficient energy storage and/or conversion, in which surface processes and transport kinetics play determining roles. This review describes recent developments in the synthesis and characterization of composites which consist of lithium metal phosphates (LiMPO(4), M = Fe, Co, Ni, Mn) coated on nanostructured carbon architectures (unordered and ordered carbon nanotubes, amorphous carbon, carbon foams). The major goal of this review is to highlight new progress in using different three dimensional nanostructured carbon architectures as support for the phosphate based cathode materials (e.g.: LiFePO(4), LiCoPO(4)) of high electronic conductivity to develop lithium batteries with high energy density, high rate capability and excellent cycling stability resulting from their huge surface area and short distance for mass and charge transport.