Solid State Module Spring Plate Compression Allowances under Cycling
Solid state spring plate allowances absorb 10 to 18 percent cell volumetric strain while bounding contact pressure between 1.0 and 4.0 MPa across cell life.
Module Endplate Stiffness
Meaning
Structural resistance to bending and deflection under the force of expanding cells determines the mechanical integrity of a battery housing. Sufficient module endplate stiffness prevents the cells from expanding too much during cycling, which would otherwise reduce their electrical performance and accelerate capacity loss. It keeps the cells compressed within their optimal pressure window.
Compressive Balance
Optimal mechanical confinement preserves the interface between the anode and cathode during long-term use. If the module endplate stiffness is too low, the central cells in the stack will expand, causing the electrolyte to squeeze out of the active areas. This localized depletion increases the internal resistance and accelerates the rate of lithium plating.
Structural Analysis
Finite element modeling calculates the expected deflection under the maximum swelling load of the cells at their end-of-life state. Engineers evaluate module endplate stiffness to ensure that the maximum deformation does not exceed the allotted geometric clearance inside the pack. This analysis determines whether additional ribbing or thicker plates are needed.
Materials Evaluation
Sourcing decisions must compare the mass and mechanical properties of different alloys to achieve the necessary rigidity without adding excess weight. Heavy steel plates provide high module endplate stiffness but reduce the overall energy density of the pack. Designers often turn to forged aluminum alloys or long-fiber composite plastics to achieve the necessary performance while saving weight.
Purchasing agreements specify the tensile yield strength of the incoming alloys to guarantee that they will not permanently deform under the cyclic swelling of the cells.