Spring Rate Non-Linearity

Force Variation

Compression pads must provide a minimum baseline pressure to prevent cell delamination when the cells are in a discharged, unexpanded state. As the cells expand during charging, the pad compresses and the force rises according to its mechanical curve. In highly non-linear materials, the resistance increases sharply after a certain compression threshold is passed.

This behavior can create excessive pressure on the cell casing at the end of charge.

Cell Swelling

Battery cells expand both reversibly during each charge cycle and irreversibly as they age over several years. The mechanical pad must absorb this long-term swelling without exerting destructive pressure on the module housing. Sourcing specifications define the allowable pressure window across the entire lifecycle of the battery.

Using a pad with a high degree of non-linearity requires very precise initial stack-up tolerances to prevent premature over-pressurization, which could otherwise deform the module walls and damage internal connections.

Material Characterization

Compression-deflection curves obtained at different temperatures and aging states help engineers select the optimal pad formulation. Silicone foams often exhibit more stable, linear behavior compared to polyurethane foams, but they carry a higher material cost. Sourcing decisions must weigh the cost difference against the risk of mechanical damage from excessive forces.

The final choice is required for ensuring the long-term safety of the battery pack.