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High-pressure synthesis and electrochemical properties of tetragonal LiMnO₂.

ABSTRACT: Tetragonal structured LiMnO₂ (t-LiMnO₂) samples were synthesized under pressures above 8 GPa and investigated as a positive electrode material for lithium-ion batteries. Rietveld analyses based on X-ray diffraction measurements indicated that t-LiMnO₂ belongs to a γ-LiFeO₂-type crystal structure with the I4₁/amd space group. The charge capacity during the initial cycle was 37 mA h g^-1 at 25 °C, but improved to 185 mA h g^-1 at 40 °C with an average voltage of 4.56 V vs. Li⁺/Li. This demonstrated the superiority of t-LiMnO₂ over other lithium manganese oxides in terms of energy density. The X-ray diffraction measurements and Raman spectroscopy of cycled t-LiMnO₂ indicated an irreversible transformation from the γ-LiFeO₂-type structure into a Li _x Mn₂O₄ spinel structure by the displacement of 25% of the Mn ions to vacant octahedral sites through adjacent octahedral sites.

SUBMITTER: Uyama T

PROVIDER: S-EPMC9082863 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

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High-pressure synthesis and electrochemical properties of tetragonal LiMnO2.

Uyama Takeshi T Mukai Kazuhiko K Yamada Ikuya I

RSC advances 20180724 46

Tetragonal structured LiMnO2 (t-LiMnO2) samples were synthesized under pressures above 8 GPa and investigated as a positive electrode material for lithium-ion batteries. Rietveld analyses based on X-ray diffraction measurements indicated that t-LiMnO2 belongs to a γ-LiFeO2-type crystal structure with the I41/amd space group. The charge capacity during the initial cycle was 37 mA h g-1 at 25 °C, but improved to 185 mA ...[more]

PMID: 35541929

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Project description:The donor-acceptor-π-conjugated (D-π-)2A fluorescent dyes OUY-2, OUK-2 and OUJ-2 with two (diphenylamino)carbazole thiophene units as D (electron-donating group)-π (π-conjugated bridge) moiety and a pyridine, pyrazine or triazine ring as electron-withdrawing group (electron-accepting group, A) have been designed and synthesized. The photophysical and electrochemical properties of the three dyes were investigated by photoabsorption and fluorescence spectroscopy, Lippert-Mataga plots, cyclic voltammetry and density functional theory calculations. The photoabsorption maximum (λmax,abs) and the fluorescence maximum (λmax,fl) for the intramolecular charge-transfer characteristic band of the (D-π-)2A fluorescent dyes show bathochromic shifts in the order of OUY-2 < OUK-2 < OUJ-2. Moreover, the photoabsorption bands of the (D-π-)2A fluorescent dyes are nearly independent of solvent polarity, while the fluorescence bands showed bathochromic shifts with increasing solvent polarity (i.e., positive fluorescence solvatochromism). The Lippert-Mataga plots for OUY-2, OUK-2 and OUJ-2 indicate that the Δμ (= μe - μg) value, which is the difference in the dipole moment of the dye between the excited (μe) and the ground (μg) states, increases in the order of OUY-2 < OUK-2 < OUJ-2. Therefore, the fact explains our findings that OUJ-2 shows large bathochromic shifts of the fluorescence maxima in polar solvents, as well as the Stokes shift values of OUJ-2 in polar solvents are much larger than those in nonpolar solvents. The cyclic voltammetry of OUY-2, OUK-2 and OUJ-2 demonstrated that there is little difference in the HOMO energy level among the three dyes, but the LUMO energy levels decrease in the order of OUY-2 > OUK-2 > OUJ-2. Consequently, this work reveals that for the (D-π-)2A fluorescent dyes OUY-2, OUK-2 and OUJ-2 the bathochromic shifts of λmax,abs and λmax,fl and the lowering of the LUMO energy level are dependent on the electron-withdrawing ability of the azine ring, which increases in the order of OUY-2 < OUK-2 < OUJ-2.

Dataset Information

High-pressure synthesis and electrochemical properties of tetragonal LiMnO₂.

Publications

High-pressure synthesis and electrochemical properties of tetragonal LiMnO<sub>2</sub>.

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