Pouch Cell Expansion

Meaning

External cell swelling defines the volume increase and thickness change exhibited by a pouch-encased lithium-ion cell during its charge-discharge cycle. Specifically, pouch cell expansion is the cumulative effect of active material swelling in the electrodes and any gas generation from electrolyte decomposition. This dimensional change is measured in millimetres using displacement transducers under a controlled clamping force.

It does not apply to rigid cylindrical or prismatic metal-can cells.

Mechanical Stress

The force exerted by this swelling can deform the module housing and apply stress to the cell electrical terminals. When pouch cell expansion is not managed, it compresses the adjacent cells and reduces the life of the entire module. This interaction demands careful thermal and mechanical design of the battery pack.

Gas Management

Trapped gases from secondary reactions can cause the pouch to swell like a pillow. If pouch cell expansion is driven by severe gassing, it indicates a mismatch in the electrolyte formulation or electrode chemistry. This phenomenon requires degas steps during the cell formation process.

System Integration

Battery pack designers must incorporate compressible foam sheets between pouch cells to absorb this mechanical expansion. Choosing cells with low pouch cell expansion allows for tighter packaging, which improves the volumetric energy density of the system. This factor is a primary consideration during cell sourcing negotiations.

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