Lithium-ion batteries have numerous advantages over conventional batteries: more compact, more compact, highly durable, long-lasting, capable of rapid charging and storing large amounts of electricity.

Due to their suitability for the growing demand for lighter and more compact electronic and electrical products, they are used in a wide range of applications, such as smartphone batteries, electric vehicles, and home energy storage systems. However, as their usage expands, incidents of lithium-ion battery related fires have been rapidly increasing.

As a result, there is a growing awareness of their potential dangers in recent years, and safety measures to prevent accidents associated with LIB have become a critical requirement.

Importance and Market Size of Lithium-Ion Batteries（LIB）

Key to Achieving Carbon Neutrality by 2050

Currently, over 120 countries and regions, including Japan, have declared their goal of achieving carbon neutrality by 2050.Fossil fuels like oil and coal, used in thermal power generation, emit significant amounts of CO₂, a major contributor to global warming, raising concerns about their environmental impact. In response, the adoption of "renewable energy" sources, such as solar and wind power, which do not emit CO₂, has been expanding.

However, these energy sources face challenges, including limited installation locations, high generation costs, and significant fluctuations in output due to weather conditions, making them difficult to provide a stable supply of large-scale energy.

One promising solution in recent years is the "lithium-ion battery (secondary battery)," which can store surplus electricity generated by renewable energy facilities. Among its applications, "stationary energy storage systems" to be installed in houses and buildings such as factories, and hospitals, as well as "automotive energy storage systems" for electric vehicles, are seen as key to ensuring a stable power supply.

Trends in the Global Energy Storage Battery Market

Looking at the trends in the global energy storage battery market, both vehicle-mounted and stationary storage batteries are expected to expand rapidly in the future, particularly with the expansion of the electric vehicle market, which is forecasted to significantly increase the demand for "automotive batteries."

Additionally, the rapid increase in power generation through solar power systems in households, along with the promotion of BCP (Business Continuity Plan) measures for cost reduction in electricity bills and resilience in industrial and commercial facilities, is expected to drive the demand for "stationary storage batteries" in homes, factories, hospitals, and other buildings.

Global Market for Secondary Batteries for ESS and Stationary Energy Storage Systems

Data referenced from Fuji Keizai Report No. 24078, "Survey on the Global Market for Secondary Batteries for ESS & Stationary Energy Storage Systems: 2040 Global Market Forecast (Base year: 2023)."

In Japan and certain states in the U.S., ordinances mandating the installation of renewable energy generation systems, such as solar power, have been introduced. (For example, in Japan, starting April 2023, buildings with a total floor area of 2,000 m² or more are required to install such systems when newly constructed or renovated.) As a result, the market size for energy storage batteries is expected to grow further across various fields.

Dangers associated with Lithium-Ion Batteries

As the demand for lithium-ion batteries continues to grow, incidents of overheating, rupture, ignition, and fires have also increased, often caused by overcharging, over-discharging, or incorrect usage.

Causes of Explosions and Fire Accidents

When external stress (such as overcharging, short circuits, vibration, impacts, or exposure to high or low temperatures) is applied during use, storage, or transportation of lithium-ion batteries, the following phenomena may occur:

Among these, "thermal runaway" requires particular attention. The electrolyte inside a lithium-ion battery can easily overheat due to rising temperatures, overcharging, or other factors. Under pressure, it may rapidly generate heat and release large amounts of flammable gas.In the worst-case scenario, this can lead to fires or explosions. Additionally, the generated heat may trigger thermal runaway in nearby batteries, creating a chain reaction and increasing the risk of widespread fire.

LIB-related Accidents Occurred in Japan and Worldwide

Current Status of Incidents Caused by LIB Thermal Runaway in Japan

This graph summarizes the number of incidents involving fire concerns related to products equipped with lithium-ion batteries in Japan over the past decade, categorized by fiscal year of occurrence.(Incidents involving fire concerns include cases where the lithium-ion batteries did not catch fire but experienced overheating, swelling, or smoke emission.)

The number of incidents has been on an upward trend, with a notable increase in FY2019 when non-genuine batteries for power tools and rechargeable vacuum cleaners became widely available. Although the trend showed a gradual decline afterward, it began to rise again in FY2022.

Factors that are thought to contribute to the increase in cases include the diversification of products using lithium-ion batteries and the growing demand for portable power sources and mobile batteries, driven by relaxed restrictions ongoing out following the COVID-19 pandemic.

Current Status of Global Incidents Caused by LIB Thermal Runaway

Fires caused by products equipped with lithium-ion batteries have been reported worldwide. According to The New York Times, the incidents associated with lithium-ion batteries were the leading cause of fire-related deaths in New York City. In FY2022, there were 220 fires caused by lithium-ion batteries in electric bicycles and electric scooters in the city, an increase of 116 incidents compared to the previous year.

The causes of these fires include not only evident user misuse (e.g., disassembly, physical impacts, improper charging methods) but also defects in lithium-ion batteries leading to spontaneous ignition.

Safety Measures Against Lithium-Ion Battery Fires

How do lithium-ion batteries overheat or catch fire?

Under normal conditions, lithium-ion batteries have their positive and negative electrodes separated by a material known as a separator. However, if battery degradation progresses due to overcharging or other factors and causes the electrolyte to oxidize, generating a large amount of gas, or if strong external forces are applied, the separator may be damaged. This can lead to reactions between the two electrode materials, which can result in a large current flow and localized overheating.

When the operating temperature exceeds the normal range of approximately 25°C to 55°C, reactions can occur between the negative electrode and the electrolyte. As the temperature continues to rise, thermal decomposition of the electrolyte begins. This process may sometimes stabilize at this point. But if, if the heat reaches around 150°C, the crystal structure of the metal oxides used in the positive electrode begins to break down, releasing oxygen.

This released oxygen acts as fuel, propelling the system into a further heat generation cycle known as "thermal runaway." In the worst-case scenario, this process results in smoke emission, ignition, or even explosions. Furthermore, as the internal temperature rises, the battery may emit not only flammable gases like hydrogen and organic compounds but also toxic gases such as carbon monoxide (CO) and hydrogen sulfide (H2S), posing significant dangers to human health.

Early Detection with Gas Sensors is the Key

Experiments on the Fire Risk of Lithium-Ion Batteries

An experiment was conducted to evaluate the response of gas sensors to gases released when lithium-ion batteries are heated beyond their normal operating temperature range using a heater.

Experimental Conditions

Six types of gas sensors (A to F) were installed in three locations - ceiling, upper level, and lower level - to detect gases emitted from a lithium-ion battery during heating under high-temperature conditions until thermal runaway occurred.

The graph's vertical axis represents temperature, while the horizontal axis represents elapsed time. The light blue dotted line indicates the surface temperature of the lithium-ion battery.

From this experiment, it was confirmed that using VOC sensors, HC gas sensors, or hydrogen (H₂) sensors enables early detection of lithium-ion battery abnormalities before thermal runaway occurs.

FIGARO's Compact, Long-Life, High-Sensitivity, and Highly Reliable Gas Sensors

Gas sensors for lithium-ion battery safety are required to have high durability and long life.FIGARO Engineering was the first in the world to successfully mass-produce Metal Oxide Semiconductor type (MOS-type) gas sensors. For over 50 years, the company has been dedicated to the research and development of various gas sensors, including MOS-type gas sensors, as well as the development and promotion of gas sensor application products.

FIGARO's proven track record in safety-related applications has been highly regarded, leading to the adoption of numerous sensors in the lithium-ion battery field.

Case Study: Company N (Multi-Environment Sensor MES-92/93)

Among the many gas sensors FIGARO supplies to various industries, some products have demonstrated over 20 years of reliable operation, proving their exceptional durability and safety.By driving technological innovation to meet the needs of customers and society, FIGARO will continue to offer an extensive lineup of high-quality products to meet diverse requirements.

FIGARO aims to contribute to the realization of safe, secure, and comfortable lives for people by providing compact, long-life, high-sensitivity, and highly reliable gas sensors.