(Invited) Organic Single-Ion Conductors for All-Solid-State Lithium Metal Batteries
Authors: Lee Sang-Young 
Published: December 2020

The all-solid-state lithium metal batteries (ASSLMBs) have recently garnered considerable attention as a next-generation energy storage system beyond current state-of-the-art lithium-ion batteries (LIBs). A key component enabling the ASSLMBs is solid-state electrolytes. Previous studies on solid-state electrolytes have mostly focused on inorganic-based ionic conductors (e.g., sulfides and oxides).[1] Despite their notable progresses in ionic conductivity, the inorganic solid electrolytes have still suffered from grain boundary resistance, poor contact/interfacial instability with electrodes, and mechanical rigidity, thus posing formidable challenges for their practical use. As an alternative to the inorganic solid electrolytes, an interest in organic single-ion conductors has newly emerged owing to their facile processability, physical flexibility, intimate contact with electrodes, versatile chemistry, and high cation transport capability.[2] In sharp contrast to conventional dual-ion polymeric conductors (e.g., a mixture of polymer matrix and lithium salts), the organic single-ion conductors do not contain freely movable anions that could often cause unwanted side reactions with electrodes and charge polarization, thereby providing improvements in electrode-electrolyte stability and electrochemical sustainability of cells.
Here, this talk presents a new class of organic single-ion conductors (OSICs) as a facile material strategy that can outperform conventional inorganic conductors. Two different design concepts[3] were proposed for the OSICs with a focus on immobilizing anions: (i) covalently tethering anions to covalent organic framework (COF) and (ii) electrostatically trapping anions by polymer–ceramic hybrid electrolytes. These OSICs allowed the cation transference numbers to reach unity (t
+>0.9), contributing to reversible stripping/plating of Li electrodes along with alleviating a concern on dendritic growth. Moreover, the structural and physicochemical uniqueness of the OSICs (in specific, directionally ordered porous structure of the COF and conformability/interfacial stability and electrophoresis-driven ion rectifying effect of the hybrid electrolytes) enabled their successful application in ASSLMBs. We envision that the OSICs described herein hold promise as an effective and versatile material platform to move ASSLMBs closer to commercialization.

References

[1] T. Famprikis, P. Canepa, J. A. Dawson, M. S. Islam, and C. Masquelier, Nat. Mater.
2019, 18, 1278.
[2] a) K. Jeong, S. Park, and S.-Y. Lee, J. Mater. Chem. A
2019, 7, 1917; b) H. Zhang, C. Li, M. Piszcz, E. Coya, T. Rojo, L. M. Rodriguez-Martinez, M. Armand, and Z. Zhou, Chem. Soc. Rev.
2017, 46, 797.
[3] a) K. Jeong, S. Park, G. Y. Jung, S. H. Kim, Y.-H. Lee, S. K. Kwak, and S.-Y. Lee, J. Am. Chem. Soc.
2019, 141, 5880.; b) S. Kim, K. H. Choi, S. J. Cho, J. Yoo, S. S. Lee, and S.-Y. Lee, Energy & Environ. Sci.
2018, 11, 321.; c) S. K. Cho, H. I. Kim, J. W. An, K. Jung, H. Bae, J. H. Kim, T. Yim, and S.-Y. Lee, Adv. Funct. Mater.
2020, accepted.

Figure 1