Analyzing the Fire Safety and Thermal Performances of the Liquid-Immersion Battery (LImB) Energy Storage System (ESS)

Abstract

Lithium-ion batteries (LIBs) are a leading energy storage technology, recognized for their high energy density and outstanding electrochemical performance. They are widely used in electric vehicles (EVs), energy storage systems (ESS), and consumer electronics. However, a significant challenge for LIBs is their susceptibility to thermal runaway, which can lead to fire and explosion. This issue is particularly important in ESS applications where a large number of high-energy cells are concentrated. In these systems, the risk of thermal runaway is affected by heat generation, the presence of combustible materials, and oxygen exposure, so safety is a top priority in all applications. A variety of safety measures have been developed to reduce the risk of fire, such as battery thermal management systems (BTMS), fire extinguishers, and other suppression methods. Existing extinguishment technologies typically rely on oxygen separation or cooling mechanisms to control combustion. Chemicals such as Novec 1230, ABC powders, and phosphoric acid-based compounds are typically used to suppress flames, while cooling systems use liquid nitrogen or refrigerants to reduce battery temperature. However, these solutions only work after a fire has started and are reactive rather than preventive. These systems also struggle to manage the challenges of high-energy systems such as ESS, where slow heat release, excessive suppression, and anaerobic propagation limit their effectiveness. Among the various LIB applications, ESS poses the greatest safety risk due to its high concentration of high-density cells. ESS plays a critical role in grid stabilization and renewable energy integration, but safety concerns have hindered its widespread adoption. For example, South Korea, a leader in ESS deployment, has reported more than 50 fire-related ESS failures, destroying approximately 1 GWh of storage capacity, equivalent to 10% of its total installed capacity. These incidents are concerning because the root cause of the fires remains uncertain, complicating the development of effective countermeasures. Given the limitations of existing fire suppression systems, recent research has explored immersion- based cooling methods that continuously submerge batteries in a coolant. This approach provides immediate heat release and continuous thermal management in the event of thermal runaway. However, practical implementation is hampered by the lack of an appropriate immersion agent that meets safety and performance criteria. Ideally, the immersion agent should be non-corrosive, electrically non-conductive, and have high thermal conductivity and capacity. Unfortunately, most existing solutions are ineffective and incomplete in suppressing fires due to poor heat dissipation. Therefore, immersion-based solutions are primarily used for fire prevention rather than active suppression. Despite these challenges, fire suppression systems play a critical role in large-scale ESS with capacities exceeding 1,000 kWh, while smaller ESS (~10 kWh) commonly used in residential environments often lack adequate fire prevention measures. This gap in safety protocols exacerbates the risks in the rapidly expanding ESS market. To ensure the safe deployment of ESS, next-generation fire prevention and suppression technologies need to go beyond conventional response strategies. Future developments should focus on integrated thermal management solutions that provide both continuous fire prevention and effective suppression to enhance safety in large-scale ESS applications. 1. Battery-in-Fire-Proof Material (BIF) Module To expand the applicability of fire extinguishers, we have developed a system that immerses batteries in a fire-resistant material (BIF) with a hermetic seal to prevent direct exposure to fire extinguishers. In this system, all battery cells are fully immersed in a liquid fire-retardant material (FPM) with high thermal conductivity and heat capacity. This setup allows for immediate fire suppression under extreme conditions while improving electrochemical performance through effective thermal management during normal operation. This study investigates the key components and practical applications of BIF technology. First, the key materials, including fire-retardant and sealing materials, are described in detail and how they are integrated into the BIF cell and module. Second, a method to prevent fire propagation by intentionally overheating a single cell within the BIF module is evaluated and the results are compared to a conventional LIB module. Third, the electrochemical performance of the BIF system is analyzed, including cycle, capacity, EIS, maximum charge rate, and operating temperature under severe conditions. The BIF system overcomes the limitations of conventional post-ignition fire suppression methods and achieves breakthroughs in fire safety and thermal management. By providing both fire prevention and thermal control, BIF technology shows significant potential in the fields of electric mobility (e.g., electric scooters, kickboards), energy storage systems (ESS), and electric vehicles (EVs). 2. LImB (Liquid Immersion Battery) ESS This study evaluates the fire prevention and suppression performance of a liquid-immersed 10kWh ESS battery system compared to a conventional LIB-ESS equipped with a standard fire extinguisher such as ABC powder. In the fire stability test, the conventional LIB-ESS system experienced thermal runaway, which resulted in rapid fire spread and system destruction, with a maximum temperature exceeding 1300°C. In contrast, the liquid-immersed system effectively mitigated the fire risk. The maximum temperature of the abused battery was only 498°C, and the adjacent cells were kept below 50°C, preventing fire spread. The initial fire was extinguished within 2 seconds, significantly reducing the size and speed of the spread. In addition to the fire suppression function, the liquid-immersed system provides improved thermal management during normal operation. Compared with conventional LIBs, it reduces the temperature rise by 6.3 times and reduces the temperature fluctuation between cells from 3.4°C to 1.5°C, ensuring stable and uniform operation. To further evaluate the practical applicability, the liquid-immersed ESS was deployed in an independent power plant and underwent actual operation tests. Despite the increasing demand for small-scale ESS, empirical studies on fire suppression and thermal management are lacking. There are few studies that systematically compare empirical data according to various fire suppression methods in ESS, leaving a gap in the development of standardized operating requirements for ESS safety. This study aims to fill this gap, establish key performance indicators for ESS safety, and contribute to the development of science-based safety guidelines for the popularization of safe and reliable ESS technology.