Toward Improved Conductivity and Electrochemical Stability of Halide Superionic Conductors for All-Solid-State Batteries

While lithium-ion batteries using conventional liquid electrolytes have been widely used from portable electronic devices to large-scale applications, such as electric vehicles and energy storage systems, their serious safety concerns have remained unsolved. Moreover, alternative electrode chemistries such as Li metal have not been stabilized by using liquid electrolytes. In this regard, all-solid-state batteries employing inorganic solid electrolytes (SEs) are considered a promising alternative.<br/>Recently, halide SEs, such as Li₃YCl₆, are newly emerging due to their prestigious advantages of excellent electrochemical/chemical oxidation stability and processability. However, a criticism of most halide SEs developed thus far is the use of costly central metal elements, such as Y, Sc, and In, with the only exception of Zr. Several descriptors affecting ionic conductivity of halide SEs have been identified: i) charge carrier concentration which is controlled by aliovalent substitution; ii) structural framework, such as trigonal, orthorhombic, and monoclinic structures; iii) structural disorder, such as disorder of Li⁺ and central metal cation disorder and stacking faults. Meanwhile, the critical drawback of halide SEs, i.e., poor cathodic stability, prohibits their use for negative electrodes, such as Li metal. In this regard, all-solid-state batteries using hybrid SEs using halide and sulfide SEs together would be practically reasonable. However, their compatibility has not been extensively investigated yet.<br/>In this presentation, we report on our recent results of our strategies to develop new halide SEs with improved ionic conductivities and electrochemical/chemical stability. Also, the results of all-solid-state batteries employing developed SEs are discussed.<br/> <br/>References<br/>[1] Hiram Kwak, Shuo Wang, Juhyoun Park, Yunsheng Liu, Kyu Tae Kim, Yeji Choi, Yifei Mo, Yoon Seok Jung, <i>ACS Energy Lett.</i> <b>2022</b>, <i>7</i>, 1776.<br/>[2] Hiram Kwak, Daseul Han, Jeyne Lyoo, Juhyoun Park, Sung Hoo Jung, Yoonjae Han, Gihan Kwon, Hansu Kim, Seung-Tae Hong, Kyung-Wan Nam, Yoon Seok Jung, <i>Adv. Energy Mater.</i> <b>2021</b>, <i>11</i>, 2003190.