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Battery Tackling Fire Hazard, Volume, and Weight Simultaneously
<(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
2025.11.05 View 2189 -
KAIST research team develops a cheap and safe redox flow battery
Redox flow batteries, one of the potential replacements for the widely used lithium-ion secondary batteries, can be utilized as new and renewable energy as well as for energy storage systems (ESS) thanks to their low cost, low flammability, and long lifetime of over 20 years. Since the price of vanadium, the most widely used active material for redox flow batteries, has been rising in recent years, scientists have been actively searching for redox materials to replace it.
On March 23, a joint research team led by Professors Hye Ryung Byon and Mu-Hyun Baik from the KAIST Department of Chemistry, and Professor Jongcheol Seo from the POSTECH Department of Chemistry announced that they had developed a highly soluble and stable organic redox-active molecule for use in aqueous redox flow batteries.
The research team focused on developing aqueous redox flow batteries by redesigning an organic molecule. It is possible to control the solubility and electrochemical redox potential of organic molecules by engineering their design, which makes them a promising active material candidate with possibly higher energy storage capabilities than vanadium. Most organic redox-active molecules have low solubilities or have slow chemical stability during redox reactions. Low solubility means low energy storage capacity and low chemical stability leads to reduced cycle performance. For this research, the team chose naphthalene diimide (NDI) as their active molecule. Until now, there was little research done on NDI despite its high chemical stability, as it shows low solubility in aqueous electrolyte solutions.
Although NDI molecules are almost insoluble in water, the research team tethered four ammonium functionalities and achieved a solubility as high as 1.5M* in water. In addition, they confirmed that when a 1M solution of NDI was used in neutral redox flow batteries for 500 cycles, 98% of its capacity was maintained. This means 0.004% capacity decay per cycle, and only 2% of its capacity would be lost if the battery were to be operated for 45 days.
Furthermore, the developed NDI molecule can save two electrons per molecule, and the team proved that 2M of electrons could be stored in every 1M of NDI solution used. For reference, vanadium used in vanadium redox flow batteries, which require a highly concentrated sulfuric acid solution, has a solubility of about 1.6M and can only hold one electron per molecule, meaning it can store a total of 1.6M of electrons. Therefore, the newly developed NDI active molecule shows a higher storage capacity compared to existing vanadium devices.
*1M (mol/L): 6.022 x 1023 active molecules are present in 1L of solution
This paper, written by co-first authors Research Professor Vikram Singh, and Ph.D. candidates Seongyeon Kwon and Yunseop Choi, was published in the online version of Advanced Materials on February 7 under the title, Controlling π-π interactions of highly soluble naphthalene diimide derivatives for neutral pH aqueous redox flow batteries. Ph.D. Candidate Yelim Yi and Professor Mi Hee Lee’s team from the KAIST Department of Chemistry also contributed to the study by conducting electron paramagnetic resonance analyses.
Professor Hye Ryung Byon said, “We have demonstrated the principles of molecular design by modifying an existing organic active molecule with low solubility and utilizing it as an active molecule for redox flow batteries. We have also shown that during a redox reaction, we can use molecular interactions to suppress the chemical reactivity of radically formed molecules.”
She added, “Should this be used later for aqueous redox flow batteries, along with its high energy density and high solubility, it would also have the advantage of being available for use in neutral pH electrolytes. Vanadium redox flow batteries currently use acidic solutions, which cause corrosion, and we expect our molecule to solve this issue. Since existing lithium ion-based ESS are flammable, we must develop safer and cheaper next-generation ESS, and our research has shown great promise in addressing this.”
This research was funded by Samsung Research Funding & Incubation Center, the Institute for Basic Science, and the National Research Foundation.
Figure 1. (a) Structures of various NDI molecules. (b) Solubility of NDI molecules in water (black bars) and aqueous electrolytes including KCl electrolyte (blue bars). (c–d) Structural changes of the molecules as the developed NDI molecule stores two electrons. (c) Illustration of cluster combination and separation of NDI molecules developed during redox reaction and (d) Snapshot of the MD simulation. NDI molecules prepared from the left, formation of bimolecular sieve and tetramolecular sieve clusters after the first reductive reaction, and a single molecule with a three-dimensional structure after the second reduction.
Figure 2. Performance results of an aqueous redox flow battery using 1M of the developed NDI molecule as the cathode electrolyte and 3.1M of ammonium iodine as the anode electrolyte. Using 1.5 M KCl solution. (a) A schematic diagram of a redox flow battery. (b) Voltage-capacity graph according to cycle in a redox flow battery. (c) Graphs of capacity and coulombs, voltage, and energy efficiency maintained at 500 cycles.
2023.04.03 View 12705