W\u3csup\u3e1,p\u3c/sup\u3e Regularity of Eigenfunctions for the Mixed Problem with Nonhomogeneous Neumann Data

We consider an eigenvalue problem with a mixed boundary condition, where a second-order differential operator is given in divergence form and satisfies a uniform ellipticity condition. We show that if a function u in the Sobolev space W1,pD is a weak solution to the eigenvalue problem, then u also belongs to W1,pD for some p\u3e2. To do so, we show a reverse Hölder inequality for the gradient of u. The decomposition of the boundary is assumed to be such that we get both Poincaré and Sobolev-type inequalities up to the boundary

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

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

Electrode Potentials Part 1: Fundamentals and Aqueous Systems

Electrochemistry deals with the interrelationship between electrical and chemical energy. Various potentials appear in electrochemistry and pertain to one another in practical cells. Understanding the electrode potential is an important step in acquiring basic knowledge of electrochemistry and extending it to specific applications. This comprehensive paper outlines the fundamentals and related subjects of electrode potentials, including electrochemical cells and liquid junction potentials. Aqueous solution systems are ideal for connecting the theoretical background of electrode potentials to practical electrochemical measurements. Accordingly, the basic electrode chemistry in aqueous systems is described in this paper, as well as several advanced concepts introduced in recent studies

Electrochemical Performance of Nanorod-like (La, Zr) Co-Doped Li-rich Li₁.₂Ni₀.₂Mn₀.₆O₂ OF ACCESS Cathodes for Use in Lithium-Ion Batteries

A lithium-rich layered structure in lithium-ion batteries (LIBs) has attracted much attention due to its high capacity of over 250 mAhg⁻¹ after activation. This could satisfy the requirements of next-generation energy-storage devices. However, a spinel-like impurity phase that forms from the pristine layered structure during cycling is considered to be harmful to the structure stability and Li⁺ mobility, resulting in undesired electrochemical performance. In this study, nanorod-like Li₁.₂Ni₀.₂Mn₀.₆O₂ with a three-dimensional architecture was synthesized by evaporative-crystallization with as-prepared nano-MnO₂ as a hard template. The structure stability and Li⁺ mobility of the nanorod-like Li₁.₂Ni₀.₂Mn₀.₆O₂ was improved by the addition of an appropriate molar ratios of (La, Zr) co-dopants. This combination exhibited outstanding capacity retention of 80.9% with a stable discharge capacity of 102 mAh g⁻¹ after 300 cycles under a high current density of 1000 mAg⁻¹ (corresponding to S C). This study suggests that the use of a multi-prong strategy that combines morphology control and co-doping should be an effective method for improving the high-rate performance of Li-rich materials

LiNi₀.₅Mn₁.₅O₄ Cathode Materials Co-Doped with La³⁺ and S²⁻ for Use in Lithium-Ion Batteries

Spherical LiNi₀.₅Mn₁.₅O₄ particles co-doped with lanthanum (La) and sulfur (S) were synthesized by a facile co-precipitation assisted solid-state annealing method with stable oxysulfide La₂O₂S (x = 0, 0.3, 0.5, 0.7, 1.0, and 1.2 at%) as a dopant. The prepared composite materials exhibited a slight shrinkage of lattice parameters without any impurity phase under x <= 0.7 at%, and the Ni/Mn disordered arrangement in the spinel lattice increased with an increase in the ratio of dopants, as confirmed by X-ray diffraction and Raman spectroscopy. X-ray photoelectron spectroscopy and electrochemical measurements also clearly indicated that the residual Mn³⁺ in the cubic lattice could be effectively eliminated with the use of La₂O₂S dopants. The composite materials showed outstanding rate and cycling performance compared with those of the pristine material. Specifically, the material doped with 0.5 at% La₂O₂S showed a high reversible capacity of 115.9 mAh g⁻¹ at 10 C, and a remarkable cycling performance of 109.2 mAh g⁻¹ even after 200 cycles. All of these extraordinary performances were attributed to the synergistic effects of La and S in the spinel structure, which induce a suitable pathway for lithium ion and a robust architecture during the electrochemical assessment

Kinetic properties of sodium-ion transfer at the interface between graphitic materials and organic electrolyte solutions

Graphitic materials cannot be applied for the negative electrode of sodium-ion battery because the reversible capacities of graphite are anomalously small. To promote electrochemical sodium-ion intercalation into graphitic materials, the interfacial sodium-ion transfer reaction at the interface between graphitized carbon nanosphere (GCNS) electrode and organic electrolyte solutions was investigated. The interfacial lithium-ion transfer reaction was also evaluated for the comparison to the sodium-ion transfer. From the cyclic voltammograms, both lithium-ion and sodium-ion can reversibly intercalate into/from GCNS in all of the electrolytes used here. In the Nyquist plots, the semi-circles at the high frequency region derived from the Solid Electrolyte Interphase (SEI) resistance and the semi-circles at the middle frequency region owing to the charge-transfer resistance appeared. The activation energies of both lithium-ion and sodium-ion transfer resistances were measured. The values of activation energies of the interfacial lithium-ion transfer suggested that the interfacial lithium-ion transfer was influenced by the interaction between lithium-ion and solvents, anions or SEI. The activation energies of the interfacial sodium-ion transfer were larger than the expected values of interfacial sodium-ion transfer based on the week Lewis acidity of sodium-ion. In addition, the activation energies of interfacial sodium-ion transfer in dilute FEC-based electrolytes were smaller than those in concentrated electrolytes. The activation energies of the interfacial lithium/sodium-ion transfer of CNS-1100 in FEC-based electrolyte solutions were almost the same as those of CNS-2900, indicating that the mechanism of interfacial charge-transfer reaction seemed to be the same for highly graphitized materials and low-graphitized materials each other