Meaning
Atomic transport within a solid or liquid occurs when a temperature gradient induces a flux of species through the material. In high power battery systems, thermomigration can move metal ions within solder joints or electrolyte components from the hot side to the cold side. This redistribution changes the local chemistry and physical structure of the device.
Molecular Flux
Atoms generally move toward the region of lower thermal energy in response to the kinetic imbalance. The rate of thermomigration depends on the steepness of the temperature gradient and the diffusion coefficient of the material. In extreme cases, this leads to the formation of voids or whiskers that can short circuit a cell.
Internal Stability
Long term exposure to uneven heat loads degrades the uniform performance of the battery electrodes. Because thermomigration alters the concentration of active materials, it can create zones of high resistance that further increase the temperature. Managing thermal uniformity is the primary defense against this effect.
Reliability Assessment
Accelerated aging tests use controlled temperature gradients to simulate years of field use in a few weeks. Observations of thermomigration allow engineers to select materials that are less prone to atomic drift. Engineered designs incorporate heat spreaders to keep internal gradients as flat as possible.
