| Challenges for fluoride-ion conductors: Designing fluoride-ion conduction into layered materials Tsuyoshi Takami1; 1KYOTO UNIVERSITY, Kyoto, Japan; PAPER: 393/SISAM/Invited (Oral) SCHEDULED: 14:50/Tue. 29 Nov. 2022/Ballroom A ABSTRACT: The fluorine atom, the second smallest after the hydrogen atom, is characterized by its large electronegativity and small polarizability [1]. Thus, it has little effect on the crystal structure, even though it causes a large electron bias in materials. Because of these unique properties, the fluorine atom is called as ‘magic element’. Fluorine has brought tremendous benefits to our lives through heat-resistant plastics, pharmaceuticals, and pesticides. The oxidation reaction of fluoride ions with a high redox potential is also promising as fluoride-ion batteries. If a solid electrolyte with a sufficient high fluoride-ion conductivity is applied to all-solid-state FIBs, operation at room temperature would become possible. PbSnF<sub>4</sub> with a layered structure exhibits a superionic conductivity (> 10<sup>-3</sup> Scm<sup>-1</sup>) at room temperature [2]. Besides it contains harmful lead in the crystal, however, it has a poor reduction resistance and there have been few reports of its incorporation into batteries. Recently, single crystals of fluorinated hexagonal BN were reported to exhibit a high in-plane fluoride-ion conductivity of 0.2 Scm<sup>-1</sup> at room temperature [3]. These reports propose that two-dimensional fluoride-ions diffusion is effective to enhance fluoride-ion conduction. In this lecture, we survey the core design principles that guide a high fluoride-ion conductivity. We conclude with a forward-looking discussion of the exciting link between fluoride-ions diffusion and layered structures in fluoride materials. References: [1] S. Dehnen, L. L. Schafer, T. Lectka, and A. Togni, Org. Lett. <b>23</b>, 9013 (2021). [2] J. M. Reau, C. Lucat, J. Portier, P. Hagenmuller, L. Cot, and S. Vilminot, Mater. Res. Bull. <b>13</b>, 877 (1978). [3] T. Takami, T. Saito, T. Kamiyama, K. Kawahara, T. Fukunaga, and T. Abe, Materials Today Physics <b>21</b>, 100523 (2021). |
