Prismatic Cell Enclosure Mechanical Stress Distribution under Solid-State Anode Expansion
Prismatic solid-state cell enclosures demand module preloads between 2 and 8 MPa with flexible interlayers to control wall deflection and dendrites.
Creep Relaxation Rates
Meaning
Decay of compressive stress over time under a constant deformation governs the long-term holding force of securing straps and compression pads in battery modules. Evaluation of creep relaxation rates allows pack designers to predict how much clamping force will remain after years of field operation. These values determine the longevity of the mechanical containment system.
Time Dependency
Viscoelastic properties of polymeric foam pads cause them to gradually lose their elastic resistance under continuous pressure. If creep relaxation rates are too high, the module holding brackets will become loose as the foam shrinks permanently over thousands of thermal cycles. The rate of relaxation increases at elevated operating temperatures.
Mechanical Consequence
Loss of holding pressure reduces the structural stiffness of the battery pack and allows individual cells to vibrate against each other. When creep relaxation rates cause the internal compression to drop below the required threshold, the lack of support allows the electrodes to expand without restraint, which speeds up capacity fade and increases the risk of internal short circuits. The cells can also slide from their positions, damaging the busbar welds and the sensing wires connected to the monitoring boards.
Test Parameter
Standardized compression fixtures measure force decay at eighty degrees Celsius over one thousand hours. These tests help select materials with low creep relaxation rates.