Li-ion cathodes based on conversion reactions such as iron fluoride (FeF 2 ) can achieve in principle high specific capacity. However, significant capacity fading is observed upon cycling. This has been attributed in part to the formation and continuous growth of a solid electrolyte interphase (SEI) layer at the cathode/electrolyte interface. In this work, scanning transmission electron microscopy, electron energy loss spectroscopy, selected area electron diffraction, and X-ray photoelectron spectroscopy were used in combination to study both the structural changes of the FeF 2 /C active material and the growth and evolution of the SEI layer upon cycling. Two main sources of capacity loss have been found. An increasing amount of Fe 2+ appeared trapped inside the SEI layer with increasing cycle number, thus resulting in the loss of active material. In addition, reconversion is strongly impeded with increasing cycle number, leaving untransformed LiF and Fe 0 upon delithiation. This correlates with the irreversible growth of a SEI layer that limits electronic and ionic transport.
The electronic structure of the Zn(II)-5-(3,5-dicarboxyphenyl)-10,15,20-triphenylporphyrin dye (ZnTPP-Ipa), chemisorbed onto ZnO(112 j 0) and TiO 2 (110) single-crystal surfaces, has been investigated by means of density functional theory (DFT) and by electron spectroscopy methods in an ultra-high-vacuum environment. The core levels (Ti 2p and Zn 2p) as well as the valence band have been probed using X-ray and ultraviolet photoemission spectroscopies, whereas the conduction band has been evaluated from inverse photoemission spectroscopy. The calculated density of states for the gas phase molecule compares well to the experimentally determined electronic structure, allowing both a simple understanding of the adsorbate electronic properties and a direct determination of the ZnTPP-Ipa frontier orbitals with respect to the substrates' band edges.
Courtesy, National Petroleum News Automatic Oxidation Apparatus fob Lubricating Oil MOST problems arising from the use of mineral oils in service are fundamentally related to oxidation of the oil. This is especially true for modern high-output engines where the demand on fuels and lubricants is becoming more critical. Fresh mineral oil consists essentially of hydrocarbons capable of furnishing satisfactory lubrication to moving parts. Under conditions of use, however, these hydrocarbons are converted to oxygenated products, properties of which we do not understand and the formation of which we can control only within limits. These products lead to lacquering, ring INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 34, No.
The chemical and structural phase evolution of ultrathin (∼5 nm) FeF 2 films upon deposition of atomic lithium in an ultrahigh vacuum environment has been studied using X-ray and UV photoemission spectroscopies, inverse photoemission spectroscopy, and transmission electron microscopy in an effort to explore the fundamental properties of the conversion reaction of this promising Li battery cathode material. Spectroscopic measurements show reduction of FeF 2 into a metallic Fe 0 phase and a LiF phase upon Li deposition. No other phases are detected. Transmission electron microscopy reveals extensive changes in the film's morphology and material reorganization upon full lithiation. The initial FeF 2 film, with grains on the order of 10 nm in diameter, phase separates into smaller (∼3 nm) interconnected Fe 0 regions surrounded by LiF. This structural modification is attributed to the large Li + ionic mobility with respect to Fe 2+ . The intrinsic nanoscale texture of the final phases is believed to aid in accommodating the extensive structural transformations that occur in this conversion reaction material during an electrochemical cycle in battery applications.
Sodium aluminoborosilicate glasses with wide-ranging compositions and structures corrode according to remarkably similar mechanisms in acidic environments.
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