Meaning
Internal heat generation occurring in specific, narrow regions of a battery cell arises from uneven electrical resistance or non-uniform current pathways. When localized joule heating becomes excessive, it creates hot spots that accelerate the aging of nearby active materials and separator membranes. This thermal non-uniformity arises from variations in electrode thickness or regional electrolyte dry-out.
Current Maldistribution
Structural flaws in current collectors or uneven compression in the cell stack force electrons to flow through restricted conductive paths. This uneven distribution of electric current triggers localized joule heating at the points of highest current density. Under high-rate charging or discharging, these high-resistance points generate heat far faster than the surrounding areas can dissipate it, leading to temperature spikes.
Thermal Concentration
Concentrated heat buildup cannot escape quickly due to the low thermal conductivity of the polymer separators and composite electrode materials. This thermal trapping ensures that localized joule heating rapidly elevates local temperatures above forty degrees Celsius, even when the average temperature of the cell remains low. The resulting temperature difference between different parts of the cell causes uneven degradation and current sharing.
Cell Degradation
Elevated regional temperatures accelerate chemical reaction rates, which speeds up the growth of the solid electrolyte interphase and degrades the separator. Minimizing localized joule heating is essential to maintain cell longevity and avoid premature capacity loss.
