Cylindrical Cell Sidewall Rupture

Cylindrical cell sidewall rupture is a significant issue in most module designs as it nearly always results in thermal propagation to neighbouring cells.

pack arranged as cells in parallel and then in series

Cylindrical cells are normally assembled in a simple rectangular or hexagonal close pack arrangement. Either option means the sidewall of one cell is close to it’s nearest neighbours.

Normally very close as cell spacing is 1 to 2mm.

The work of Read et al [1] shows that Sidewall Rupture = Thermal Runaway.

cylindrical cell sidewall rupture — *Read et al also show a link between nail penetration depth and likelihood of sidewall rupture [1]*

Quinn et al [2] show that the internal location of Thermal Runaway (TR) initiation is often unpredictable but correlates to the cell failure mode and the consequent risks. A spectrum of risk scenarios should be considered in battery pack engineering. High temperature and pressure during TR may stress cell features, some of which are prone to failure. Vents placed on the top, bottom, or both ends of a cell are intended to relieve excess cell pressure, release electrolyte before it can combust, and provide a dedicated ejection path for TR products.

Sidewall ruptures are more likely in:

High energy density cells leads to increased energy generation during TR
Thinner cell casings used to reduce parasitic mass and/or increase inner active volume