Why do lithium batteries fail during thermal runaway?

Causes of Thermal Runaway

Thermal runaway in lithium batteries occurs when the internal temperature of the battery exceeds the safe operating range, typically between 50°C to 70°C. This can be triggered by various factors such as overcharging, short circuits, or physical damage to the battery. When the temperature exceeds this range, the chemical reaction between the electrodes and electrolyte accelerates, releasing heat and flammable gases.

Physical and Chemical Processes Involved

During thermal runaway, the lithium ions in the battery begin to decompose, releasing gas and further increasing the internal pressure. This can cause the battery casing to rupture, leading to a fire. In addition, the rapid release of heat can also cause the electrolyte to degrade, leading to a loss of electrical conductivity and further exacerbating the thermal runaway process.

Preventing Thermal Runaway

To prevent thermal runaway, it is essential to monitor the battery’s internal temperature and prevent overcharging or over-discharging. This can be achieved by implementing a Battery Management System (BMS) that regulates the charge and discharge cycles of the battery. Additionally, using a lithium battery with a built-in thermal management system, such as a heat sink or a phase change material, can also help to mitigate the risk of thermal runaway.