Design Factors for New Halide Superionic Conductors for All-Solid-State Batteries

Replacing flammable organic liquid electrolytes with inorganic solid electrolytes (SEs) has been regarded as the promising solution to address the requirements of better safety and higher energy density, compared to conventional lithium-ion batteries. Thus far, sulfide and oxide SEs have been the most extensively investigated candidates. Unfortunately, they possess the counteracting pros and cons. While sulfide SEs are mechanically sinterable, which eases the fabrication of ASSBs, they suffer from the poor (electro)chemical oxidation stabilities. The advantage of oxide SEs, the much better (electro)chemical oxidation stabilities is offset by the brittle properties. Newly emerging halide SEs have attracted enormous attention because they present the advantages of sulfide and oxide SEs simultaneously, that is, the mechanical sinterability and excellent (electro)chemical oxidation stability. As-developed halide SE materials thus far include trigonal Li₃YCl₆ (0.51 mS cm^-1), monoclinic Li₃InCl₆ (1.5 mS cm^-1), monoclinic Li₃ScCl₆ (3.0 mS cm^-1), and trigonal Li_2+xZr_1-xFe_xCl₆ (max. ~1 mS cm^-1). It has been revealed that the multiple factors, such as the Li concentration, the structural framework and disorder, affect the ionic conductivities.<br/>In this presentation, we report on our recent results of new halide superionic conductors whose conductivities are enhanced by abnormal effect. High ionic conductivities of ≥1 mS cm^-1 are achieved by the new approach. Moreover, layered oxide cathodes using new halide SEs in all-solid-state cells show the stable cycling at elevated temperature.<br/> <br/>References<br/>[1] H. Kwak, D. Han, J. Lyoo, J. Park, S. H. Jung, Y. Han, G. Kwon, H. Kim, S.-T. Hong, K.-W. Nam, Y. S. Jung, <i>Adv. Energy Mater.</i> <b>2021</b>, <i>11</i>, 2003190.<br/>[2] K. H. Park, Q. Bai, D. H. Kim, D. Y. Oh, Y. Zhu, Y. Mo, Y. S. Jung, <i>Adv. Energy Mater.</i> <b>2018</b>, <i>8</i>, 1800035.