Meaning
Mechanical force applied to the exterior of a battery cell or pouch maintains the internal layers in close physical contact. Maintaining external stack pressure prevents the delamination of electrodes from the separator during the volume changes associated with ion intercalation. This compression is usually provided by rigid plates or elastic foam spacers within a battery module.
Proper loading ensures uniform current distribution and reduces the risk of localized lithium plating.
Pouch Integrity
Soft packaging requires consistent clamping to counteract the gas generation and thermal expansion that occur during normal cycling. If external stack pressure is insufficient, the resulting gaps increase the internal resistance and lead to uneven heat distribution. Excessive force must be avoided to prevent the separator from crushing or the pores from closing.
Fatigue Resistance
Periodic expansion and contraction cycles test the ability of the housing to maintain a steady load over the service life of the pack. If the clamping mechanism relaxes, the loss of external stack pressure allows the active materials to shift or buckle. This mechanical failure leads to a rapid decline in capacity as the electrical pathways between the particles are broken.
Measurement Standard
Load cells or pressure sensitive films verify that the force is distributed evenly across the entire face of the cell. Uniform external stack pressure is measured in kilopascals and must stay within the range specified by the cell manufacturer. Most lithium ion chemistries require between 50 and 300 kilopascals to optimize the cycle life and safety of the system.
