The compact storage ring, AURORA was installed in Ritsumeikan University in 1995 and started its operation in the next year. The SR center was established in the same year. Since then, the ring has been operated without any serious trouble until 2021, when a water leak trouble happened in the RF cavity in the ring. It took 9 months to restart operation. As a result of it, we could not use SR almost one year. This was the first serious trouble, but it might be a good opportunity to look back upon the past activities of the SR center and to think over the future plans. I have been the director of the center for twelve years from fiscal 2006 to fiscal 2018. As a living witness of the center, it might be worthwhile to review the history of the SR center. The history of the center can be roughly divided to two phases: the first is from 1996 to 2006 and the second from 2006 to the present. In the first phase, the most brilliant scientific output was the fabrication of micro-devices using the LIGA technique, while in the second phase, scientific activities have been focused on characterization of functional materials, especially secondary batteries by using synchrotron radiation-based spectroscopies. In this review article, I will describe the development of beamlines and selected activities in each phase from my own personal judgement and also address the future plans of the center.

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This article summarizes the upgrading of the hard X-ray XAFS beamlines at the SR Center of Ritsumeikan University since 2009. BL-3 is a general-purpose XAFS beamline equipped with a focusing mirror and can be used up to 9 keV. The BL-3 is equipped with a 3-element SSD, and the measurement by the fluorescence-yield method is possible in addition to the measurement by the transmission method. It is also possible to perform in-situ XAFS measurement under a reaction gas atmosphere at elevated temperatures. BL-4 is a non¬focusing XAFS beamline which can measure up to about 10 keV, and the imaging XAFS measurement is possible using a two-dimensional detector. It is effective in analyzing the reaction distribution in the plane of a flat sample such as the electrode of a rechargeable battery. BL-5 is a special beamline which uses white X-rays and is equipped with two kinds of time-resolved XAFS instruments with a dispersive X-ray optics. A dispersive XAFS instrument, which simultaneously achieves XAFS measurements at the absorption edge of two elements using two curved crystals at the same time, is useful for analyzing the interelement correlation to the function of the material. The vertically dispersive XAFS instrument using a cylindrically bent crystal is capable of the time-resolved XAFS measurement for one-dimensional region of the sample. It is possible to perform XAFS measurement by simultaneously decomposing time and space for the phenomenon, for which the inhomogeneous distribution changes with time in the plane of a flat sample.

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Soft X-ray absorption spectroscopy (SXAS) is one of powerful tool to characterize the electronic structure for analysis of rechargeable battery. This review introduces the recent studies of the battery electrode and electrolyte using SXAS in Ritsumeikan SR center. In the introduction, the advantage of SXAS is explained. Then, after overviewing the previous X-ray absorption spectroscopic study using the conventional cathode material, LiNiO2, the charge compensation mechanism related in lithium-rich layered cathode material, Li1.16Ni0.15Co0.19Mn0.50O2 is discussed. To measure operando X-ray absorption near edge structure at soft X-ray region, originally designed measurement cell has been developed, which is utilized to the analysis of nonequilibrium phenomena during battery reaction. SXAS detects the surface state on electrode materials, which has been applied to the analysis of surface degradation on LiCoO2 cathode. SXAS in SR center has also contributed on the analysis of next-generation rechargeable battery. Cathode materials newly developed for magnesium rechargeable batteries and potassium batteries were measured, which indicated the charge/discharge reaction contributing the ligand-hole state. Analysis of liquid electrolyte for magnesium rechargeable batteries was performed. These SXAS measurements have an important role to characterize the unknow phenomena during laboratory studies on battery reaction.

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