Toward new frontiers : Encounter and synergy of state-of-the-art astronomical detectors and exotic quantum beams

Program B03-1	Development of highly spin polarized lithium and oxygen radioisotope beams for the study of battery materials
Principal Investigator	MIHARA, Mototsugu (Osaka University)

Lithium ion batteries (LIBs) and fuel cells (FCs), which exhibit excellent performance in rechargeability and electric power generation, respectively, have been widely in practical use in recent years and are becoming increasingly important. The next generation of LIB and FC devices such as the all-solid-state LIB and the solid state oxide FC (SOFC), respectively, are attracting a lot of attention. Here, creating or finding new materials that have high ionic conductivity is a key issue to achieve high performance in these new devices. In order to evaluate such ion conducting materials, reliable data for the ionic conductivity is indispensable. The nuclear magnetic resonance (NMR) technique is a promising method of the ion-conductivity measurement, which usually utilizes stable nuclei as NMR probes that are naturally abundant. However, in some cases the NMR sensitivity becomes insufficient because of low concentration of probe nuclei in materials. Since in the case of the LIB charge and discharge are performed using the migration of lithium ions, there can be a place where the Li ion concentration becomes low during the charge-discharge cycles. Concerning the oxygen NMR, the natural abundance of oxygen probe nucleus is quite low, so that it has been difficult to advance the NMR study of the SOFC materials.

We approach this problem by using lithium and oxygen radioisotopes (RIs) ⁸Li and ¹⁹O as NMR probes with which we aim at measuring the ion conductivity in LIB and FC materials. The beta-NMR technique utilizing the beta-ray emission from RI enables the detection of NMR with extremely high sensitivity which is more than 1010 times higher than that of the conventional NMR. In order to achieve this, we develop a new method to produce spin polarized ⁸Li and ¹⁹O beams. Nuclear reactions in inverse kinematics will be attempted, by which highly polarized and intense RI beams are expected. This will

Schematic drawing of the operating mechanisms of the all-solid-state lithium-ion battery (left) and the solid state oxide fuel cell (right).
lead to the study of Li ion conduction in the low concentration region or providing a new oxygen NMR probe. In addition, a small energy spread in the RI beam can be achieved in this method, which will make it possible to scan a specific part of an active device such as electrode and electrolyte by controlling the implantation depth of the beam. In this research plan, we aim to establish a new method to evaluate ion conducting materials for LIB and FC devices.

Members

Reference Materials

• M. Mihara, “Fundamentals of β-NMR and its new developments in materials science studies (in Japanese),” J. Surf. Sci. Soc. Jpn. 38, 188–193 (January 2017), DOI: 10.1380/jsssj.38.188 .
• K. Matsuta, T. Minamisono, M. Mihara et al., “Nuclear moments as a probe of electronic structure in material, exotic nuclear structure and fundamental symmetry,” Hyperfine Interact. 220, 21–28 (2013), DOI: 10.1007/s10751-013-0847-0.
• T. Minamisono et al., “Electromagnetic moments of the β-emitting nucleus ¹⁹O,” Phys. Lett. B 457, 9–16 (1999), DOI: 10.1016/S0370-2693(99)00468-2.
• K. Matsuta et al., “Creation of spin polarization in unstable nuclei and correlation-type experiments,” Nucl. Instrum. Methods Phys. Res. A 402, 229–235 (1998), DOI: 10.1016/S0168-9002(97)81652-X.