What Are the Common Causes of Thermal Runaway in Lithium Batteries?

Thermal runaway is the worst-case failure mode of a lithium cell, in which internal heating becomes self-accelerating. It is rare in well-designed products, but understanding its triggers helps you avoid them.

Typical triggers

The main causes are overcharge, internal short circuits, external crushing or puncture, exposure to high ambient heat and charging at very low temperature, which can cause lithium plating. Overcharge drives excessive lithium extraction and gas generation, while mechanical damage pierces the separator and initiates an internal short. Charging below the recommended temperature range is a hidden but common cause.

How to reduce the risk

Use a charger matched to the cell's voltage and current limits, include a properly rated protection board, avoid physical damage and keep the device within its specified temperature range. Reputable suppliers also screen cells and design packs with fuses and vents. Respect these boundaries and thermal runaway remains an unlikely event rather than an expected one.

Finally, never continue using a swollen, dented or unusually hot pack, and source cells from suppliers who can provide test reports rather than relying on unverified bargain units. Most safety incidents trace back to ignoring one of these basic boundaries.