Analytical Sciences

Excitation Energy Dependence for the Li 1s X-ray Photoelectron Spectra of LiMn₂O₄

Junichi TSUJI,*¹ Manabu FUJITA,*¹ Yuichi HARUYAMA,*² Kazuhiro KANDA,*² Shinji MATSUI,*² Naoshi OZAWA,*³ Takeshi YAO,*³ and Kazuo TANIGUCHI*⁴

*1 Toray Research Center, Inc., 3-3-7 Sonoyama, Otsu, Shiga 520-8567, Japan
*2 University of Hyogo, 3-2-1 Kouto, Kamigori, Ako-gun, Hyogo 678-1205, Japan
*3 Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
*4 Osaka Electro-Communication University, 18-8 Hatsu-cho, Neyagawa, Osaka 572-8530, Japan

The Li 1s XPS (X-ray Photoelectron Spectroscopy) spectra of LiMn₂O₄, which is one of the major positive-electrode materials in lithium-ion rechargeable batteries, and MnO₂ as a reference material, were measured by a laboratory-type XPS spectrometer. The Li 1s peak was not observed in the spectra excited by the Mg K_α line (1253.6 eV), because the Li 1s peak overlapped the background of the Mn 3p peak of LiMn₂O₄. The photoionization cross section of Mn 3p was larger than that of Li 1s for Mg K_α excitation. Therefore, the XPS measurement of LiMn₂O₄ by soft X-ray synchrotron excitation was carried out at beamline BL-7B on NewSUBARU synchrotron facility. Excitation energies of 110, 120, 130, 140, 150 and 151.4 eV were selected. The Li 1s peak was clearly observed in these XPS spectra. In order to investigate the excitation energy dependence, the area ratio of the Li 1s and Mn 3p peaks in the XPS spectra was plotted against the excitation energy. As a result, when the excitation energy was 110 eV, the area ratio had the maximum value.

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