According to reports, researchers at the National Science and Technology Research Institute (UNIST) in Ulsan, South Korea, demonstrated a new solvent-free single-lithium ion conductive covalent organic skeleton. The study was led by Sang-Young Lee and Sang Kyu Kwak, professors at the UNIST School of Energy and Chemical Engineering. During the research, the team demonstrated a new concept of solid ionic conductors that selectively pass lithium ions through the ion channels. Since they are solid and can efficiently transport lithium ions, they are expected to be the raw materials for next-generation batteries, such as high-voltage batteries or lithium metal batteries.
At present, lithium-ion batteries use highly flammable liquid electrolytes, which are very prone to fire or explosion. As an alternative, solid electrolytes are under development, but their ionic conductivity is lower than that of liquid electrolytes. In particular, many solid electrolytes have limitations in terms of improving battery performance because the migration path of ions is tortuous and complicated.
Professor Lee uses porous crystal materials as ionic conductors, such as covalent organic framework (COF), to solve this problem. The ion conductivity is greatly improved by regularly arranging lithium ion channels inside the material. The first author of the study, Dr. Kihun Jeong of the UNST School of Energy and Chemical Engineering, said: The newly developed ionic conductor is a solid phase carrier that does not use liquid at all, and achieves the conductive behavior of solid single lithium ions.
Single lithium ion conductive behavior means that ideally only lithium ions are transported through the electrolyte. Since lithium ions are cations, they are easily moved together with anions. Unnecessary anion migration can cause side reactions on the electrode surface, reducing battery performance. In this study, an anion was immobilized in the path through which lithium ions passed, and an organic skeleton structure was synthesized using an anion monomer paired with lithium ions. In this way, only lithium ions flow along the channel, achieving an ideal flow state. Researchers have theoretically determined the use of computational chemistry. In computational science, lithium ions move along regularly aligned oxygen atoms in the ionic conductor channels.
Professor Lee said: This study provides a new direction for the design of solid ionic conductors, laying the foundation for the development of 'high performance solid electrolytes'. This is critical for the commercialization of next-generation batteries, including all solid-state batteries. Such a conductor can selectively and efficiently transport lithium ions, and it is not necessary to use an organic solvent which is explosive, which is of extraordinary significance. These ionic conductors are not only suitable as electrolytes for solid-state batteries, but also for highly active lithium metal electrodes.