KAIST

<(From Left) Professor Hye Ryung Byon, Ph.D candidate Rak Hyeon Choi, Professor Chang Yun Son>

Lithium-metal batteries are garnering attention as the next-generation high-energy battery set to replace existing lithium-ion batteries. However, commercialization has been difficult due to the high fire risk associated with using flammable liquid electrolytes. As an alternative to solve this, 'organic solid electrolytes' with flexibility were proposed, but their slow lithium-ion transfer rate at room temperature limited their practical application. Korean researchers have succeeded in developing a solid electrolyte that enhances lithium-ion mobility by 100 times and operates at room temperature.

KAIST announced on November 4th that a research team led by Professor Hye Ryung Byon from KAIST Department of Chemistry, in collaboration with Professor Chang Yun Son's team from Seoul National University, has developed a new organic solid electrolyte film that operates stably even at room temperature.

The research team fabricated a solid electrolyte about 1/5 the thickness of a human hair using a new material called 'Covalent Organic Framework (COF)', which has a porous structure with uniformly arranged holes.

The developed COF electrolyte features a porous crystalline structure similar to the Metal Organic Framework (MOF), which won the 2025 Nobel Prize in Chemistry, but with significantly enhanced chemical stability in the battery operating environment.

The team meticulously arranged lithium-ion transporting functional groups at regular intervals, designing the structure so that lithium ions, which previously only moved at high temperatures, could rapidly move along these functional groups even at room temperature. This implemented a solid electrolyte structure where the lithium-ion migration path can be precisely controlled at the molecular level.

Specifically, the research team introduced a 'dual sulfonated functional group' into the nanopores to facilitate the easy detachment (dissociation) and movement of lithium ions, creating a channel that allows lithium ions to move rapidly along the shortest linear path. Molecular Dynamics (MD) simulations confirmed that this structure lowers the energy required for lithium ion movement, enabling fast migration with less energy and stable operation even at room temperature.

The fabricated electrolyte film is made via a 'Self-assembly' method, resulting in a very smooth surface and uniform structure. Consequently, it adheres perfectly to the lithium metal electrode, allowing ions to move more stably when traveling between electrodes.

<Figure 1. Synthesis process and structural/electrochemical properties of ultrathin covalent organic framework (COF) films according to thickness.(a) Synthesis process of ultrathin COF solid electrolyte, (b) Changes in thickness and surface roughness of COF films according to monomer concentration,(c) Changes in crystallinity of COF solid electrolytes with variations in morphology and thickness, (d) Ionic conductivity characteristics of COF solid electrolytes depending on morphology and thickness,(e) Rate capability of lithium metal–lithium iron phosphate (LiFePO₄) batteries, (f) Cycle life characteristics of lithium metal–lithium iron phosphate batteries >

As a result, the developed electrolyte showed a lithium-ion migration speed 10 to 100 times faster than conventional organic solid electrolytes. When applied to a lithium-iron phosphate battery based on lithium metal, it maintained over 95% of its initial capacity even after 300 charge/discharge cycles, demonstrating high stability with almost no energy loss (Coulombic efficiency of 99.999%).

<Figure 2. Molecular dynamics simulation analysis of the lithium-ion conduction mechanism in the COF solid electrolyte. (a) Lithium-ion (turquoise spheres) conduction pathways through two distinct ionic conduction subchannels within the COF, (b) Two-dimensional free energy landscape of each migration pathway obtained from metadynamics simulations >

Professor Hye Ryung Byon stated, "This research represents a step forward in the commercialization of lithium-metal batteries by realizing an organic solid electrolyte capable of fast lithium-ion migration even at room temperature," adding, "Combining it in a hybrid form with inorganic solid electrolytes could improve interfacial stability issues."

The first author of this research is Rak Hyeon Choi, a graduate student in the KAIST Chemistry Department, and the results were published in the international journal Advanced Energy Materials (October 5, 2025 issue).

Paper Title: Room-Temperature Single Li⁺ Ion Conducting Organic Solid-State Electrolyte with 10⁻⁴ S cm⁻¹ Conductivity for Lithium Metal Batteries, DOI: 10.1002/aenm.202504143

This achievement was supported by LG Energy Solution and KAIST's Frontier Research Laboratory (FRL), as well as the National Research Fou