Abstract
Cylindrical Li-ion batteries (cells) typically have safety vents in the positive terminal to enable the release of gases that build up inside the battery and thus help reduce the effects of thermal runaway, including fire and explosion. However, the vents are not always effective, and it is critical to understand why. This paper overviews various vent designs and presents two case studies of vents in cylindrical Li-ion batteries that failed to operate properly. The first case study concerns a Sony VCT5 18650 Li-ion battery in which thermal runaway caused the cylindrical casing (can) to rupture. The second case study involves an Ampking 20700 Li-ion battery in which thermal runaway caused side-wall rupture of the casing. In both cases, the vents did not function as intended. Computed tomography (CT) scanning was used to investigate the internal structure of the battery to assess the failure mechanisms of the failed vents. These cases raise concerns about the efficiency, reliability, and safety of some current vent designs.
Highlights
Li-ion batteries are widely used for energy storage owing to their high energy density and high capacity
Catastrophic battery accidents resulting in thermal runaway have increased with the growing popularity of battery-operated products
Safety vents are designed to prevent the rupture of batteries by releasing gases and pressure buildup resulting from thermal runaway
Summary
Li-ion batteries (cells) are widely used for energy storage owing to their high energy density and high capacity. The increased temperature causes the generation of gases, and the increase in internal pressure can lead to battery rupture, fire, and explosion. The gases were trapped near the negative terminal of the battery, and burnt layers prevented the safety vent at the positive terminal from properly working.
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