Direct Probing of Lattice-Strain-Induced Oxygen Release in LiCoO and Li MnO without Electrochemical Cycling.

Since the recognition of a significant oxygen-redox contribution to enhancing the capacity of Li transition-metal oxide cathodes, the oxygen release and subsequent structural variations together with capacity fading are critical issues to achieve better electrochemical performance. As most previous reports dealt with the structural degradation of cathodes after electrochemical cycling, it is fairly difficult to clarify how substantial the effect of lattice strain on the oxygen release will be while exclusively ruling out any electrochemical influences. By utilizing nanoindentation and mechanical surface polishing of single-crystal LiCoO and Li MnO , the local variations of both the atomic structure and oxygen content are scrutinized.

Local-electrostatics-induced oxygen octahedral distortion in perovskite oxides and insight into the structure of Ruddlesden-Popper phases.

As the physical properties of ABX perovskite-based oxides strongly depend on the geometry of oxygen octahedra containing transition-metal cations, precise identification of the distortion, tilt, and rotation of the octahedra is an essential step toward understanding the structure-property correlation. Here we discover an important electrostatic origin responsible for remarkable Jahn-Teller-type tetragonal distortion of oxygen octahedra during atomic-level direct observation of two-dimensional [AX] interleaved shear faults in five different perovskite-type materials, SrTiO, BaCeO, LaCoO, LaNiO, and CsPbBr. When the [AX] sublayer has a net charge, for example [LaO] in LaCoO and LaNiO, substantial tetragonal elongation of oxygen octahedra at the fault plane is observed and this screens the strong repulsion between the consecutive [LaO] layers.

Atomic-scale unveiling of multiphase evolution during hydrated Zn-ion insertion in vanadium oxide.

An initial crystalline phase can transform into another phases as cations are electrochemically inserted into its lattice. Precise identification of phase evolution at an atomic level during transformation is thus the very first step to comprehensively understand the cation insertion behavior and subsequently achieve much higher storage capacity in rechargeable cells, although it is sometimes challenging. By intensively using atomic-column-resolved scanning transmission electron microscopy, we directly visualize the simultaneous intercalation of both HO and Zn during discharge of Zn ions into a VO cathode with an aqueous electrolyte.

Atomic-Scale Direct Identification of Surface Variations in Cathode Oxides for Aqueous and Nonaqueous Lithium-Ion Batteries.

The electrochemical (de)intercalation reactions of lithium ions are initiated at the electrode surface in contact with an electrolyte solution. Therefore, substantial structural degradation, which shortens the cycle life of cells, is frequently observed at the surface of cathode particles, including lithium-metal intermixing, phase transitions, and dissolution of lithium and transition metals into the electrolyte. Furthermore, in contrast to the strict restriction of moisture in lithium-ion cells with nonaqueous organic electrolytes, electrode materials in aqueous-electrolyte cells are under much more reactive environments with water and oxygen, thereby leading to serious surface chemical reactions on the cathode particles.

In situ synthesis of supported metal nanocatalysts through heterogeneous doping.

Supported metal nanoparticles hold great promise for many fields, including catalysis and renewable energy. Here we report a novel methodology for the in situ growth of architecturally tailored, regenerative metal nanocatalysts that is applicable to a wide range of materials. The main idea underlying this strategy is to selectively diffuse catalytically active metals along the grain boundaries of host oxides and then to reduce the diffused metallic species to form nanoclusters.

Conductive Nature of Grain Boundaries in Nanocrystalline Stabilized BiO Thin-Film Electrolyte.

Stabilized BiO has gained a considerable amount of attention as a solid electrolyte material for low-temperature solid oxide fuel cells due to its superior oxygen-ion conductivity at the temperature of relevance (≤500 °C). Despite many research efforts to measure the transport properties of stabilized BiO, the effects of grain boundaries on the electrical conductivity have rarely been reported and their results are even controversial. Here, we attempt quantitatively to assess the grain boundary contribution out of the total ionic conductivity at elevated temperatures (350-500 °C) by fabricating epitaxial and nano-polycrystalline thin films of yttrium-stabilized BiO.