Nondestructive High-Sensitivity Detections of Metallic Lithium Deposited on a Battery Anode Using Muonic X-rays.

Metallic Li deposited on the anode is known to induce short circuiting and degradation of the charge capacity of Li-ion batteries. However, no reliable technique is currently available to observe such Li metal without removing the case of the battery. An elemental analysis using muonic X-rays is proposed here because of its unique properties of nondestructive measurement, high sensitivity to light elements, and depth resolution. We demonstrated that this technique can be applied to detection of Li deposited on the surface of an anode containing Li ions, using a fully charged anode with Li deposited due to overcharge in an Al-laminated plastic pouch. The basis for the detection method is the difference in the atomic Coulomb capture ratio of the negative muons between the Li metal and ions. We have found, as a result, that the intensity of the muonic X-rays from metallic Li was approximately 50 times higher than that from Li ions. Consequently, the Li metal on the anode was clearly distinguishable from the intercalated Li ions in the anode. Furthermore, measurements of two overcharged anodes with 1.3 and 2.7 mg of metallic Li deposition, respectively, indicated that this technique is suitable for quantitative analysis. Distribution analysis is also possible, as shown by a preliminary observation on an overcharged anode from the back side. Therefore, this technique offers a new approach to the analysis of Li deposited on the anode of a Li-ion pouch battery.

Nuclear Magnetic Field in Solids Detected with Negative-Muon Spin Rotation and Relaxation.

Using an intense negative muon (µ^{-}) source, we have studied the internal magnetic fields in a powder sample of magnesium hydride (MgH_{2}). By extracting the signal from the µ^{-} captured on Mg nuclei, we found that the negative muon spin rotation and relaxation (µ^{-}SR) spectra clearly showed a Kubo-Toyabe-type relaxation, which indicates a random magnetic field at the Mg site. The field distribution width obtained is very consistent with the predicted value at the Mg site estimated by dipole field calculations, supporting our claim to have observed the nuclear magnetic fields of hydrogens in MgH_{2}. As is the case with µ^{+}SR, µ^{-}SR promises to soon be an indispensable tool for materials analyses.

Li-ion diffusion in Li intercalated graphite C6Li and C12Li probed by µ+SR.

In order to study a diffusive behavior of Li+ in Li intercalated graphites, we have measured muon spin relaxation (µ+SR) spectra for C6Li and C12Li synthesized with an electrochemical reaction between Li and graphite in a Li-ion battery. For both compounds, it was found that Li+ ions start to diffuse above 230 K and the diffusive behavior obeys a thermal activation process. The activation energy (Ea) for C6Li is obtained as 270(5) meV, while Ea = 170(20) meV for C12Li. Assuming a jump diffusion of Li+ in the Li layer of C6Li and C12Li, a self-diffusion coefficient DLi at 310 K was estimated as 7.6(3) × 10-11 (cm2 s-1) in C6Li and 14.6(4) × 10-11 (cm2 s-1) in C12Li.

A novel challenge of nondestructive analysis on OGATA Koan's sealed medicine by muonic X-ray analysis.

OGATA Koan (1810-63) was a physician and the director of Tekijuku, and he contributed to Western medicine in the late Edo period. Osaka University preserves two of his medicine chests. One of the chests, which was used in his last years (the second chest) contained 22 glass bottles and 6 wooden cylinders. These bottles and cylinders contained formulated medicines; however, about half cannot be opened because of the long-term storage. It is necessary to comprehend the physical property of both the containers and their contents for investigation of this adequate preservation method; however, destructive analysis is not allowed. To analyze the medicines sealed in the glass bottles, we focused on muonic X-ray analysis, which has high transmittance. First, we certified the analytical methods using a historical medicinal specimen preserved in Osaka University. Thereafter, we applied the method on the bottles stored in the second chest. X-ray fluorescence identified the glass of those bottles to be lead potash glass. Among these bottles, we chose the bottle with the label "," which contains white powdered medication, for muonic X-ray analysis. We identified the contents of the medication in the glass to be Hg2Cl2. Through this study, we first applied muonic X-ray analysis on the medical inheritances and succeeded to detect the elements contained both in the container and in the contents of the sealed bottle. This would be a new method for nondestructive analysis of such cultural properties.

Investigation of ionic and anomalous magnetic behavior in CrSe2 using 8Li ß-NMR.

We have studied a mosaic of 1T-CrSe2 single crystals using ß-detected nuclear magnetic resonance of 8Li from 4 to 300 K. We identify two broad resonances that show no evidence of quadrupolar splitting, indicating two magnetically distinct environments for the implanted ion. We observe stretched exponential spin lattice relaxation and a corresponding rate (1/T 1) that increases monotonically above 200 K, consistent with the onset of ionic diffusion. A pronounced maximum in 1/T 1 is observed at the low temperature magnetic transition near 20 K. Between these limits, 1/T 1 exhibits a broad minimum with an anomalous absence of strong features in the vicinity of structural and magnetic transitions between 150 and 200 K. Together, the results suggest 8Li+ site occupation within the van der Waals gap between CrSe2 trilayers. Possible origins of the two environments are discussed.

Magnetic phase diagram of K2Cr8O16 clarified by high-pressure muon spin spectroscopy.

The K2Cr8O16 compound belongs to a series of quasi-1D compounds with intriguing magnetic properties that are stabilized through a high-pressure synthesis technique. In this study, a muon spin rotation, relaxation and resonance (µ+SR) technique is used to investigate the pressure dependent magnetic properties up to 25 kbar. µ+SR allows for measurements in true zero applied field and hereby access the true intrinsic material properties. As a result, a refined temperature/pressure phase diagram is presented revealing a novel low temperature/high pressure (pC1 = 21 kbar) transition from a ferromagnetic insulating to a high-pressure antiferromagnetic insulator. Finally, the current study also indicates the possible presence of a quantum critical point at pC2 ~ 33 kbar where the magnetic order in K2Cr8O16 is expected to be fully suppressed even at T = 0 K.