Electrochemical Surface Analysis of LiMn₂O₄ Thin-film Electrodes in LiPF6/Propylene Carbonate at Room and Elevated Temperatures

Degradation of LiMn₂O₄ in LiPF₆-based electrolyte solution is complicated due to the influence of PF₆⁻ anion. Decomposition of PF₆⁻ anion accelerates both of dissolution of manganese ion and surface-film formation. In this study, surface states of LiMn₂O₄ thin-film electrodes in LiPF6/propylene carbonate (PC) derived from the surface-film formation were investigated using redox reaction of ferrocene and spectroscopic analyses. The spectroscopic analyses suggested that properties of the surface film depended the operation temperature (30°C and 55°C); a thinner surface film composed of LiF and PC decomposition products formed on LiMn₂O₄ at 30°C and a thicker surface film was formed at 55°C. The redox reaction of ferrocene clearly showed that LiMn₂O₄ was completely passivated at 30°C, while it was partially passivated at 55°C, indicating the surface film formed at 55°C was not compact and LiMn₂O₄ was exposed to the electrolyte solution. It was one of the causes of the rapid degradation of LiMn₂O₄ at elevated temperatures in LiPF6-based electrolyte solution

Impact of Hydrogen Peroxide on Carbon Corrosion in Aqueous KOH Solution

Impact of hydrogen peroxide on carbon corrosion is investigated by immersion tests of catalyst-deposited highly oriented pyrolytic graphite (HOPG) samples to an aqueous solution of 1.0 mol dm⁻³ KOH + 5 mmol dm⁻³ H₂O₂. The surfaces of the HOPG samples are observed with field-emission scanning electron microscopy and X-ray photoelectron spectroscopy. HOPG without catalyst shows almost no morphological change while the distribution of C-O and C=O functional groups increases. In contrast, Pt-loaded HOPG exhibits the formation of scars and COO functional groups, which shows a relatively severe carbon corrosion reaction resulting in CO₃²⁻ formation. Since the Pt-loaded HOPG after the immersion test to 0.5 mol dm⁻³ H₂SO₄ + 5 mmol dm⁻³ H₂O₂ shows much smaller scars, it can be concluded that hydrogen peroxide corrodes Pt-loaded carbon more severely in the alkaline electrolyte solution than the acid electrolyte solution. Ag-loaded HOPG also shows the scars, while the sizes of scars are much smaller than those on the Pt-loaded HOPG. In contrast, MnOx and CoOx-loaded HOPGs exhibit no scar and minor oxygen-containing functional groups than the HOPG without catalyst, whereas MnOx and CoOx-loaded HOPGs shows larger scars than Pt and Ag-loaded HOPGs after electrochemical carbon corrosion test

Primary type specimens of some domestic species in Japan, and their taxonomic status

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Electron spin phase relaxation of phosphorus donors in nuclear spin enriched silicon

We report a pulsed EPR study of the phase relaxation of electron spins bound to phosphorus donors in isotopically purified 29^Si and natural abundance Si single crystals measured at 8 K.Comment: 5 pages, 3 figure

Relation between Mixing Processes and Properties of Lithium-ion Battery Electrode-slurry

The mixing process of electrode-slurry plays an important role in the electrode performance of lithium-ion batteries (LIBs). The dispersion state of conductive materials, such as acetylene black (AB), in the electrode-slurry directly influences the electronic conductivity in the composite electrodes. In this study, the relation between the mixing process of electrode-slurry and the internal resistance of the composite electrode was investigated in combination with the characterization of the electrode-slurries by the rheological analysis and the alternating current (AC) impedance spectroscopy. Some of the electrode-slurries showed higher value and gentler slope of the dynamic storage modulus in the low-angular-frequency region and higher thixotropic index than the others depending on the way of the mixing process and the AB content, agreeing with the low electronic volume resistivities of the corresponding composite electrodes and the electrode-slurries, which indicates the AB network growth. The results suggested that the low-viscosity state when AB and active electrode material are mixed contributes to the dispersive AB network. (C) The Author(s) 2021. Published by ECSJ