Module Compression Pad Mechanics under Non Linear Swelling Force Profiles
Non-linear swelling forces mandate hyperelastic compression pads that hold module interfacial pressure between 0.02 MPa and 0.60 MPa over full cell life.
Thermal Expansion Superposition
Meaning
Mathematical modeling methods combine the mechanical deformation caused by temperature changes with the expansion caused by chemical phase changes. Applying thermal expansion superposition allows pack engineers to predict the total volumetric change of lithium-ion cells during high-power cycling.
Deformation Modeling
Cells expand due to both thermal expansion from resistive heating and electrochemical swelling from lithium intercalation. In thermal expansion superposition, these two independent sources of strain are summed to calculate the peak thickness of the cell under load. This calculation is verified by measuring displacement under various temperature and state of charge conditions.
Overlooking either of these components can result in an underestimation of the physical pressure on the module housing.
Engineering Application
The results help designers size the compressible foam pads that sit between cells in the module. By predicting the peak force during high-current charging, engineers can ensure that the compression remains within safe limits. This work is required to prevent the mechanical stress from damaging the cell structure.
Design Consequence
Accurate superposition models reduce the need for overly conservative mechanical margins in the module housing. This optimization allows for tighter packing of the cells, which increases the volumetric energy density of the battery pack.