Dangerous Discarded Lithium-Ion Batteries: "Thermal Runaway" Above 3.94 V Residual Voltage

Thermal Abuse Tests on Cylindrical Discarded Lithium-Ion Batteries
Fire Behavior Varies Depending on Voltage

An empirical analysis has found that even discarded lithium-ion batteries can cause intense thermal runaway and fires when exposed to external heat if they retain a certain level of electrical energy.

On November 10, the National Fire Research Institute of the National Fire Agency said that thermal abuse tests conducted to assess fire risks based on the residual voltage of discarded lithium-ion batteries confirmed thermal runaway accompanied by flames under certain voltage conditions.

Discarded lithium-ion batteries retain residual electrical energy even after they are no longer used in devices, creating a significant fire risk during collection, storage, transport, and recycling. In fact, fires and explosions that were difficult to extinguish occurred in January 2024 at the crushing process of a waste battery recycling company in Pyeongtaek, Gyeonggi Province, and in April 2020 at the separation process of a waste battery processing company in Goryeong County, North Gyeongsang Province.

In response, the institute sorted collected cylindrical discarded lithium-ion batteries by residual voltage and conducted thermal abuse tests by applying heat from the outside at a constant rate. It precisely compared and analyzed changes in temperature over time, gas emissions and flame formation, patterns of thermal runaway, and heat release rates during fires.

The results showed a stark difference in how the discarded batteries responded depending on their average residual voltage.

At an average residual voltage of 3.45 V, the batteries released off-gas and leaked electrolyte, but did not undergo thermal runaway. By contrast, at an average residual voltage of 3.94 V or higher, battery temperatures surged, triggering intense thermal runaway accompanied by flames.

The institute said the tests demonstrated that even discarded batteries can cause large-scale fires when exposed to an external heat source if their voltage remains above a certain level. It also noted that gas emissions and flammable electrolyte leaks were observed even under low-voltage conditions where thermal runaway did not occur. It therefore emphasized that safety management must rigorously control residual energy and surrounding heat sources throughout the storage and collection process.

The National Fire Research Institute plans to produce educational materials and informational resources for personnel involved in collecting and storing discarded lithium-ion batteries and working at recycling facilities, using footage of the tests and the data analysis results, and distribute them to relevant sites.

Kim Yeonsang, head of the National Fire Research Institute, said, "We will actively share relevant information so that our research findings can make a tangible contribution to fire prevention at facilities that handle these batteries and to improving awareness of safety management."

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