Rechargeable lithium batteries have rapidly risen to prominence as fundamental devices for green and sustainable energy development. Lithium batteries are now used as power sources for electric vehicles. However, materials innovations are still needed to satisfy the growing demand for increasing energy density of lithium batteries. In the past decade, lithium-excess compounds, Li 2 MeO 3 (Me = Mn 4+ , Ru 4+ , etc.), have been extensively studied as highcapacity positive electrode materials. Although the origin as the high reversible capacity has been a debatable subject for a long time, recently it has been confirmed that charge compensation is partly achieved by solid-state redox of nonmetal anions (i.e., oxide ions), coupled with solid-state redox of transition metals, which is the basic theory used for classic lithium insertion materials, such as LiMeO 2 (Me = Co 3+ , Ni 3+ , etc.). Herein, as a compound with further excess lithium contents, a cation-ordered rocksalt phase with lithium and pentavalent niobium ions, Li 3 NbO 4 , is first examined as the host structure of a new series of high-capacity positive electrode materials for rechargeable lithium batteries. Approximately 300 mAh·g −1 of high-reversible capacity at 50°C is experimentally observed, which partly originates from charge compensation by solid-state redox of oxide ions. It is proposed that such a charge compensation process by oxide ions is effectively stabilized by the presence of electrochemically inactive niobium ions. These results will contribute to the development of a new class of high-capacity electrode materials, potentially with further lithium enrichment (and fewer transition metals) in the close-packed framework structure with oxide ions.battery | lithium | anion redox | positive electrode T o realize sustainable energy development in the future, it is widely admitted that the substitution of energy sources for fossil fuels must be considered. An efficient energy storage system using an electrochemical method, such as rechargeable lithium batteries (Li-ion batteries, LIBs), potentially provides the solution to meet these tough challenges. Now, electric vehicles equipped with an electric motor and LIB have been launched in the market, and LIBs are starting to substitute for fossil fuels as power sources in the transportation system using the technology of internal combustion engines. Since their first appearance as power sources for portable electronic devices in 1991, the technology of LIBs has now become sufficiently sophisticated. Nevertheless, the demands for a further increase in energy density are still growing to extend the driving distance for electric vehicles.In 1980, LiCoO 2 with a cation-ordered rocksalt structure (layered type) was first proposed as a positive electrode material for LIBs (1) , etc.), which are also classified as having cation-ordered rocksalt-type structures (2), have been extensively studied as potential high-capacity electrode materials, especially for the Mn 4+ system (Li 2 MnO 3 ) (3-7). Li 2 MnO 3...

Solvent-dependent host-guest chemistry and favoring of otherwise disfavored conformations of large guests has been achieved with an adaptive, self-assembled Fe(II)4L4 coordination cage. Depending on the counterion, this face-capped tetrahedral capsule is soluble either in water or in acetonitrile and shows a solvent-dependent preference for encapsulation of certain classes of guest molecules. Quantitative binding studies were undertaken, revealing that both aromatic and aliphatic guests bind in water, whereas only aliphatic guests bind in acetonitrile. The flexibility of its subcomponent building blocks allows this cage to expand or contract upon guest binding, as studied by VT-NMR, thereby ensuring strong binding of both small and large guests. Upon encapsulation, large guest molecules can adopt conformations which are not thermodynamically favored in the free state. In addition, the chirotopic inner phase of the cage renders enantiotopic guest proton signals diastereotopic in specific cases.

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The oxidative addition of an Si-X a-bond (X = H or Si) to M(PH3):! (M = Pd or Pt) is investigated with ab initio MOMP4, SD-CI, and CCD methods. Geometries of reactants, transition states (TS), and products are optimized at the MP2 level. Although addition of an f-polarization function on Pt and Pd changes the activation energy (E,) and the reaction energy ( A E ) little, addition of a d-polarization function on P decreases the exothermicity considerably. Although the MPZoptimized geometries differ somewhat from the SCF-optimized ones, E, and A E calculated for the SCF geometries are almost the same as E, and A E for the MP2 geometries. E, and A E hardly change upon going from MP4SDQ to SD-CI and CCD, whereas they fluctuate somewhat at the MP3 and MP4DQ levels. The instability of Hartree-Fock wave function is not observed even at the TS. These results indicate that a single reference wave function can be used for these oxidative addition reactions. Unexpectedly, the Si-Si and Si-H oxidative additions to Pd(PH3)2 proceed with a lower E, than those to Pt(PH&, while the former are less exothermic than the latter. These results are explained in terms of bond energies and the electronic structure of the TS.

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