From smartphones to electric vehicles and medical devices, numerous electronic devices in our daily lives depend on lithium batteries. They are lightweight, charge quickly, and have a long lifespan, making them optimal power sources in any setting. However, there are still limitations that have not been fully resolved. If subjected to shock or exposed to heat, the battery can overheat or lead to an explosion in a phenomenon known as 'thermal runaway.'
Technologies that significantly reduce the risks associated with lithium batteries have been developed both domestically and internationally. Innovations include new materials that fundamentally prevent thermal runaway and technologies that integrate fire extinguishers within batteries. There are also sensors that detect overheating risks early. These are safety technologies designed to protect batteries from heat.
◇Fire extinguisher integrated within lithium batteries
Zhang Ying, a researcher at the Institute of Chemistry of the Chinese Academy of Sciences, developed a flame-retardant material that suppresses fires in lithium metal batteries at high temperatures and presented the findings in the Proceedings of the National Academy of Sciences (PNAS) on the 14th (local time). Flame retardancy refers to the property of material that reduces flammability.
Lithium batteries generate current by allowing lithium ions to move from the anode to the cathode while inducing the movement of electrons in the opposite direction during discharge. Among them, lithium metal batteries use lithium metal as the anode material, which allows them to store nearly ten times the energy compared to conventional lithium-ion batteries that use graphite anodes. This is because while graphite anodes only store some lithium ions between layers in a crystalline structure, lithium metal anodes can store lithium ions throughout the entire electrode.
However, lithium metal batteries are still limited in commercial use due to fire hazards. When thermal runaway occurs, combustible gases and oxygen are simultaneously released, increasing the risk of fire or explosion.
The research team developed a polymer-based flame-retardant material. When applied to the electrodes of lithium metal batteries, this material suppresses the release of oxygen in high-temperature environments while simultaneously emitting substances that inhibit flames. This means that when the battery reaches a certain temperature, it functions like a 'micro fire extinguisher.'
Tests using the flame-retardant polymer material in lithium metal batteries showed that the self-heating rate decreased to 1/10,000 compared to existing batteries. Conventional batteries began overheating at temperatures above 100 degrees Celsius, soaring to 1,000 degrees in 13 minutes before exploding. In contrast, batteries with the polymer material did not exceed 220 degrees and did not ignite.
The research team noted that the flame-retardant polymer material could be applied not only to lithium metal batteries but also to lithium-ion or lithium-sulfur batteries. This implies that it can be used in various fields such as electric vehicles, electronic devices, and electric aircraft. Researcher Zhang said, "In the short term, it can be relatively easily applied to existing battery production processes," adding, "In the long term, it could be used alongside new battery designs or material development."
◇Fires in electric vehicle batteries, starting from the cell
In Korea, technologies for ensuring lithium battery safety are evolving as well. Hyundai Mobis developed a technology to prevent battery overheating last year, and in April, it unveiled an 'automatic fire extinguishing system for battery cells' that automatically suppresses electric vehicle battery fires.
Unlike existing fire extinguishing systems that spray extinguishing agents over the entire battery, this newly unveiled technology analyzes the battery's temperature, voltage, and pressure to accurately detect anomalies and concentrate extinguishing agents only on the affected area. This prevents heat transfer to surrounding cells and preemptively blocks thermal runaway. A cell is the smallest unit of a battery, with multiple cells connected to create a module, and modules are assembled to form a battery pack.
Lee Seung-jun, a researcher at Hyundai Mobis, explained through the Hyundai Motor Group's media channel 'HMG Journal,' "To use the limited extinguishing agents most effectively, we developed a structure that focuses on the cell with anomalies," adding, "It can operate proactively even before a fire occurs to prevent accidents."
The technology developed by Hyundai Mobis can be applied while maintaining the existing battery structure, making it easily adaptable to various electric vehicle battery systems. Moreover, the extinguishing device takes up very little space, allowing the battery's size or capacity to remain unchanged.
Recently, major countries including Europe, China, and India have mandated by law that, when a battery fire occurs, it must delay thermal runaway for a certain period or completely prevent heat from transferring to surrounding cells. The technology from Hyundai Mobis has garnered attention as a practical alternative that meets global safety standards.
◇Early detection of warning signs in solid-state batteries from the outside
Professor Lee Hyun-wook and his research team at the Ulsan National Institute of Science and Technology (UNIST) developed sensor technology capable of detecting the 'short circuit,' a chronic issue in solid-state batteries, at an early stage. This research was published in the ACS Energy Letters last month and was selected as the most read paper for a month.
When a lithium battery is subjected to shock, the liquid electrolyte, which is the pathway for lithium ions, is lost, causing the electrodes to come into direct contact and ignite a fire. Solid-state batteries replaced the liquid electrolyte with a solid one, thus resolving this issue. However, during the charging process, if lithium crystals grow on the electrodes like branches, it may cause a short circuit, leading to a fire. This phenomenon is known as lithium dendrite formation.
The research team attached pressure sensors and displacement sensors to the outside of the battery. By analyzing minute pressure and thickness changes within the cell in real time, they detected early signs of lithium dendrite formation. When dendrites grow vertically, internal pressure and thickness changes become distinctly evident. By observing this pattern, short circuits can be predicted early.
The research team also identified conditions that could suppress dendrite formation. They found that increasing the pressure applied to the battery cell from above or coating the surface of the lithium metal electrode with silver or magnesium could prevent the growth of lithium dendrites.
Professor Lee Hyun-wook stated, "It is significant that warning signs inside solid-state batteries can be detected early using external sensors," adding, "This will become a key technology supporting the stability and commercialization of solid-state batteries."
References
PNAS (2025), DOI: https://doi.org/10.1073/pnas.2501549122
ACS Energy Letters (2025), DOI: https://doi.org/10.1021/acsenergylett.5c01570