Understanding Lithium-ion Battery Fires: Mechanisms, Causes, and Forensic Indicators

Dustin Herte, CFEI, Energy Forensics Group

Lithium-Ion Battery Fires: Mechanisms, Causes, and Forensic Analysis

Lithium-ion batteries are ubiquitous, powering everything from e-bikes to electric power tools. However, their high energy and power density, errors in manufacturing and user error can all contribute to occasional dangerous fires or explosions. For product liability attorneys and investigators, understanding how these fires start—and what evidence remains—is crucial for determining liability.

Thermal Runaway

The core mechanism of a lithium-ion battery fire is "thermal runaway," which is a self-sustaining chain reaction where internal temperature rises uncontrollably. When a cell overheats or is damaged, the internal materials break down exothermically. This reaction vaporizes the flammable electrolyte, which can vent and ignite. Once initiated, the heat can trigger neighboring cells, turning a single cell failure into a full-scale fire or explosion.

Common Causes of Failure

Battery failures generally result from manufacturing defects or abuse. The four primary causes are:

• Overcharging: Charging a battery beyond its voltage limit causes electrode breakdown and dendrite formation, leading to internal shorts. While Battery Management Systems (BMS) are designed to prevent this, BMS failures can result in thermal runaway.

• Over-Discharging: Draining a cell below safe limits can dissolve the copper anode. Upon recharging, this copper redeposits in the form of dendrites and creates internal shorts, potentially triggering a fire.

• Physical Damage and Defects: Crushing or puncturing a battery causes immediate internal short circuits.

• External Heat: Exposure to high ambient temperatures or external fires can destabilize cells. A battery can be a victim of a house fire rather than the cause, complicating the investigation.

  
  

Forensic Indicators

Investigating these fires is challenging because the evidence is often destroyed, leaving behind only charred debris. However, specific forensic indicators help distinguish the fire's origin.

• Battery Remains: Investigators look for remnants, such as copper and aluminum foils. Perforations or melt patterns on the foils can help to indicate if an internal short circuit sparked the blaze.

• Point of Origin: If burn patterns radiate outward from the battery’s location, it suggests the battery was the ignition source. However, if the battery is found in an area where the fire spread later, it may be a victim.

• Cause vs. Effect: A battery that initiated a fire often exhibits a ruptured casing and scattered contents due to internal pressure. In contrast, a battery that burned passively (as a victim) may be intact, especially if it had a low charge state at the time of the fire.

• Analytical Tools: Non-destructive testing, such as X-ray or CT scanning, can reveal internal cell damage without disturbing fragile evidence.

  
  

Conclusion

For legal practitioners, technical details regarding char patterns, ruptured cells, and chemical remnants are vital for proving whether a battery was defective or misused. By analyzing these forensic indicators, investigators can assign responsibility and determine if a manufacturing flaw, a failure of safety circuits, or user error caused the incident.