Multi Axial Creep Fatigue Damage Accumulation in Vacuum Brazed Battery Pack Cooling Structures
Vacuum brazed aluminum cooling plates fail under coupled multi-axial creep-fatigue when pressure pulses interact with static cell swelling constraints.
Thermal Expansion Gradient
Meaning
Spatial variation in dimensional change across a cell or pack surface occurs due to uneven temperature distribution during charging and discharging. An uneven thermal expansion gradient can cause localized stress concentrations within the battery casing. This phenomenon leads to accelerated aging of the cell in hotter zones.
Physical Mechanism
Local temperature differences alter the rate of material expansion across different regions of the cell body. When a thermal expansion gradient develops, the hotter sections of the battery experience more volume change than the cooler sections. This discrepancy creates internal mechanical shear stresses that can damage the internal electrode stack.
Design Consequence
Enclosure engineering must account for these uneven physical changes to prevent structural failure or cell deformation. Minimising the thermal expansion gradient requires the use of efficient liquid cooling plates and thermal interface materials. It ensures that the pressure across the cell surface remains uniform during operation.
Measurement Technique
Precise laser displacement sensors or tactile pressure sheets map these localized movements during high-current cycling tests. Determining the thermal expansion gradient helps engineers locate regions of high heat generation in prototype cells. They use this data to optimise the cell internal tab layout and thickness.
It allows developers to refine cell construction before starting commercial production lines.