Experts share insights as concerns about EV battery fires linger

EV Batteries. (Yonhap)

Concerns about fires caused by electric vehicle battery failure continue to linger in the aftermath of a series of these incidents. Conflicts among residents have arisen in some apartment complexes over the banning of parking EVs in underground garages or prohibiting their charging.

Understanding the scientific causes of EV fires, prevention methods, and how to respond during a fire can help alleviate vague and excessive fears about EVs.

To understand EV fires, it is important to first grasp the structure and characteristics of the batteries used in EVs.

EVs typically use high-performance batteries called lithium-ion batteries, which are similar to those found in smartphones, tablets, and laptops.

The structure of lithium-ion batteries can be broadly divided into the anode, cathode, electrolyte, and separator.

The electrolyte serves as a medium for lithium ions to move between the anode and cathode. The separator prevents direct contact between the anode and cathode, thus avoiding chemical collisions.

The key component is the separator. If the separator is damaged and the anode is directly connected, the temperature rises, and the electrolyte begins to boil. As the electrolyte boils, it releases gas and causes the battery to swell, ultimately leading to an explosion.

The causes of separator damage can be classified into three main categories – manufacturing defects, overcharging/discharging, and external impacts.

Manufacturing defects occur when foreign substances, such as metals introduced during battery production, grow into protrusions that damage the separator during use.

“When the separator is compromised, small heating occurs inside the battery, and the internal temperature continues to rise,” Hanyang University Professor Oh Ki-yong said. “Once the chain reaction begins, it becomes impossible to stop, which is the biggest problem.”

Overcharging refers to the state where the battery is charged beyond its designed capacity. This causes significant heating, generating flammable gases inside the battery, which in turn leads to changes in the electrolyte and damage to the separator.

Although EV batteries include battery management systems (BMS) to prevent overcharging, it can occur if these systems do not function properly. Some automakers and battery manufacturers have implemented temporary measures, such as limiting charging amounts, after fires occurred in specific EV models to prevent overcharging.

Just as dangerous as overcharging is over-discharging, which happens when a battery is not charged in time and its capacity is completely depleted. Abnormal electron supply due to over-discharging can cause the electrodes to melt, resulting in heat generated by chemical reactions such as that generated by overcharging.

External impacts may not immediately cause ignition, but damage to the separator can lead to delayed fires. EV drivers should therefore ensure that their batteries are checked for safety after any collisions.

Fires can escalate into major fires due to the “thermal runaway” phenomenon associated with lithium-ion batteries. The battery structure comprises stacked battery cells that form battery modules, which are then stacked to create battery packs. This layered design means that if one cell explodes, the fire can spread to adjacent cells, causing a chain reaction.

“Comparing thermal runaway energy, dynamite has an energy of 2,083Wh per kg, grenades have 385Wh per kg, and lithium-ion batteries can weigh up to 290Wh per kg, which is about 75.3 percent of a grenade’s explosion power,” Doh Chil-hoon, a researcher from the Korea Electrotechnology Research Institute, said.

The fires can also cause severe damage to their surroundings and often lead to large-scale incidents. Due to the nature of lithium-ion batteries, flammable gases can be expelled under high pressure, causing flames to spread horizontally, which can also lead to explosions.

Given the variety and complexity of causes, it is practically impossible to prevent EV fires entirely, making it challenging for EV drivers to prevent and control fires.

The primary responsibility for minimizing thermal runaway falls on automakers and battery manufacturers, experts noted. Automakers should minimize fire spread within the vehicle by using heat-resistant materials and enhancing design to allow sufficient time for passenger evacuation.

Battery manufacturers also play a crucial role. Currently, enhancing performance, such as increasing driving range, directly correlates with heightened fire risks. Increasing the nickel content in the cathode, or minimizing external protective materials and modules, is necessary to improve driving distance, which increases chemical instability as well as vulnerability to impacts.

Developing technologies that can simultaneously enhance energy density and fire resistance is likely to determine the competitiveness of battery manufacturing moving forward.

Solid-state batteries are gaining attention as a dream battery because they replace liquid electrolytes and separators with solid materials, significantly reducing the risk of chemical ignition while increasing battery density.

Numerous products besides EVs also use lithium-ion batteries, of which electric scooters pose a particularly significant fire risk.

“Electric scooters contain 60 cylindrical batteries connected in parallel, resulting in prolonged thermal runaway and frequent re-ignition,” the National Fire Research Institute’s Na Yong-woon said. “The Ministry of Trade, Industry, and Energy and the Korean Agency for Technology and Standards must strengthen certification systems for electric scooters.”

From a driver’s perspective, experts noted that managing battery charge levels is essential to prevent overcharging and over-discharging. To safely and effectively use EVs, it is advisable to maintain battery charge levels between 20 to 80 percent and perform a slow charge once a month for balanced charging.

Regular battery safety inspections can also increase the chances of fire prevention. In Korea, battery inspections can be performed at private inspection centers using the electronic device diagnostic system introduced by the Korea Transportation Safety Authority.