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A binary system of Li2TiO3–LiMnO2 is systematically examined by joint experimental and theoretical studies as electrode materials for Li storage applications. Increase in a fraction of Li2TiO3 effectively activates anionic redox, and thus holes are reversibly formed on oxygen by electrochemical oxidation. Such holes are energetically stabilized through π-type interaction with Mn t2g orbital as suggested by theoretical calculation. However, excess enrichment of Li2TiO3 fractions in this binary system results in the oxygen loss as an irreversible process on delithiation because of a non-bonding character for Ti–O bonds coupled with the formation of O–O dimers, which are chemically and electrochemically unstable species. Additionally, detailed electrochemical study clearly shows that Li migration kinetics is relatively slow, presumably coupled with low electronic conductivity. Nevertheless, nanosizing of primary particles is an effective strategy to overcome this limitation. The nanosized sample prepared by mechanical milling delivers a large reversible capacity, ∼300 mA h g−1, even at room temperature and shows much improved capacity retention. Formation and stabilization of holes for the nanosized sample are also directly evidenced by soft X-ray absorption spectroscopy. From these results, factors affecting the reversibility of anionic redox as emerging new chemistry and its possibility for energy storage applications are discussed in more details.

The photodegradation of methylene blue (MB) was investigated by UV–vis spectroscopy and liquid chromatography-mass spectrometry analyses. For this purpose, undoped, nitrogen-doped, and gold nanoparticle (AuNP)-doped TiO2 thin films for photodegradation were prepared, along with cuboid-shaped WO3 powder samples, some loaded with Pt and the others with Cu. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure analyses revealed that nitrogen atoms were incorporated into the TiO2 crystal both interstitially like KNO3 and NaNO2 and substitutionally like TiN. Mass analysis revealed that MB was degraded under visible-light irradiation via N-demethylation, cleavage of C–N and C–S bonds, and addition reactions of −OH and = O. Products with over m/z values greater than 400 were detected in the solutions degraded by the samples not doped with metals, but not in those degraded by metal-doped samples, which may have been due to the large adsorption capability of the metal-doped samples and their rapid degradation of MB.

A 41.6MgO-27.1B2O3-31.2SiO2 glass was synthesized by container-less levitation method. B K-edge X-ray absorption near edge structure (XANES) spectroscopy was used to quantify the coordination of boron in the as-made glass, resulting in ~72% of boron in 3-fold coordination. Raman spectroscopy indicated that the glass structure includes depolymerized borate units, which are pyroborate (B2O54−) and ring and/or chain-type metaborate (B3O63−, (BO2O−)∞) groups. The structural changes in the glass under hydrostatic condition were investigated by high-pressure Raman spectroscopy within a diamond anvil cell at pressures up to 8.5 GPa. On the borate structure, metaborate groups decreased with pressure. In contrast, triborate groups, which include tetrahedrally coordinated boron and have a fully polymerized borate network, increased; suggesting that the coordination transformation of B and polymerization were induced via compression. However, the modification of the borate structure units seems to be reversible at least up to 8.5 GPa. As for the silicate network, Q0 and Q1 structures were responsible to compression. Specifically, Q0 could be replaced by Q1 with elevating pressure, which means that the silicate network becomes polymerized with pressure. Whereas, structure of glass samples recovered from the pressure higher than 5 GPa displayed depolymerized silicate network, as dissociation of Q2 to Q1. The observed structural changes in the silicate network implied a partial change of the coordination number of Si4+ ions, which can be enhanced by the presence of a modifier cation with high field strength such as Mg2+.

We investigated the oxygen contributions on delithiation process of different types of layered 3d transition metal oxides, Li2TiO3, Li2MnO3, and LiCoO2, using X-ray spectroscopies with the aid of density functional theory calculations. In delithiatied LiCoO2, electrons are extracted from highly hybridized Co 3d and O 2p orbitals without O2 loss. In Li2TiO3, the hybridized Ti 3d and O 2p orbitals at the valence band is mainly contributed by O 2p orbitals, and delithiated Li2TiO3 loses oxygen as the electrons are extracted. Li2MnO3 exhibits some hybridization. In delithiated Li2MnO3, a certain amount of oxygen is lost, but the large amount of oxidized O anions remains as peroxide and superoxide-like states, which would work as the redox active species. Therefore, the degree of hybridization between metal 3d and O 2p orbitals is a key factor to influence the stability of O anion redox during the oxidation process, which determines the electrode performance.

A solid electrolyte interphase (SEI) formed on a model LiCoO2 electrode was analyzed by the ultra-soft X-ray absorption spectroscopy (XAS). The data of Li K-, B K-, C K-, O K-, and Co L-edges spectra for the SEI film on the electrode were collected using three detection methods with different probing depths. The electrode was prepared by a pulsed laser deposition method. All the spectral data consistently indicated that the SEI film containing lithium carbonate was instantly formed just after the soak of the electrode into the electrolyte solution and that it decomposed during the repeated charge–discharge reactions. The decomposition of the SEI film seems to cause the deterioration in lithium ion battery cycle performance. By adding lithium bis(oxalate) borate (LiBOB) to the electrolyte the decomposition could be suppressed leading to longer cycle life. It was found that some of the Co ions at the electrode surface were reduced to Co(II) during the charge–discharge reactions and this reaction could also be suppressed by the addition of LiBOB.