Long Term Interconnect Creep and Weld Fatigue under Cyclic Thermal Load in Heavy Formats
Thermal expansion and cell swell induce cyclic shear stresses that trigger weld fatigue and interconnect creep, requiring compliance flexure loops.
Terminal Swelling
Meaning
Electrochemical expansion describes the dimensional increase at the electrical poles of a lithium ion cell as internal layers thicken during cycling. Terminal swelling occurs when solid electrolyte interphase buildup or material degradation pushes the current collector against the housing. This physical deformation exerts pressure on internal structural components, potentially leading to mechanical failure of the contact points or venting of the electrolyte.
Dimensional Threshold
Engineering requirements limit the allowable thickness variance to avoid stress fractures within the module assembly. Manufacturers specify a maximum tolerance in millimetres for the casing deformation throughout the operational lifespan of the unit. Exceeding this boundary compromises the structural integrity of the pack and risks short circuits from internal component displacement.
Degradation Mechanism
Chemical reactions between the electrolyte and the electrode surfaces consume active lithium ions to form dense byproduct layers. These layers accumulate over time as the cell undergoes repeated charging cycles, occupying more volume than the original electrode material. The process accelerates under elevated temperature conditions or high current rates, which foster faster growth of the solid interface.
Force Distribution
Internal mechanical load maps define the areas of greatest pressure where the cell architecture resists expansion. Rigid enclosures transfer this force directly to adjacent cells, which risks a cascading failure if the pack lacks compliant buffers. Proper design accounts for this expected growth by leaving small voids or using spring loaded restraint systems to control the output force.