Meaning
Mechanical pressure applied to battery pouch or prismatic cells maintains internal contact and manages expansion during cycling. Applying a specific compressive pre load prevents the delamination of active materials from the current collectors. Lithium ions moving into the anode cause physical swelling that must be restrained to ensure a long cycle life.
This force is typically provided by the module frame or end plates during assembly.
Clamping Pressure
Measurement of the applied force ensures that the cells are neither too loose nor too tightly packed. If the compressive pre load is insufficient, the layers inside the cell may separate and increase internal resistance. Excessive pressure can crush the separator and lead to an internal short circuit.
Engineers specify a target pressure in pascals or newtons to be applied during the module bolting process.
Structural Integrity
Rigid frames are required to maintain the force as the battery ages and the materials naturally expand. The design of the module must account for the peak force reached at a full state of charge. During the life of the battery, the compressive pre load changes as the internal chemistry evolves.
Sophisticated enclosures use springs or foam pads to compensate for these variations. High strength materials like aluminum or steel are used for the end plates to prevent bending under the internal load. This structural stability is a requirement for safety in crash scenarios.
Cycle Longevity
Restraining the physical growth of the electrodes reduces the rate of mechanical degradation. Maintaining a consistent compressive pre load ensures that the electrolyte remains evenly distributed across the electrode surface. This prevents the formation of dry spots that could lead to localized overheating.
Managing the expansion of the electrode stack is necessary for the long term health of the battery.
