Glass transition temperature

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Potting compound

A liquid resin — polyurethane, silicone or epoxy, sometimes foamed — poured around cells or electronics and cured into a solid block. It fixes cells against vibration, insulates them and can slow thermal propagation; some structural packs fill every gap between cylindrical cells with it. The cost is mass and a pack that is hard to repair or recycle.

Structural adhesive

A load-bearing adhesive, usually epoxy, polyurethane or acrylic, that bonds cells to each other, to the tray or to the lid so the cell block becomes part of the structure. Cell-to-pack and cell-to-chassis designs rely on it, at the price of cells that are hard to replace or to separate for recycling.

Coefficient of thermal expansion

The fractional change in length per kelvin of temperature change. Aluminium expands about 23 ppm/K, copper 17, steel 12 and most plastics several times more, so joined parts in a pack — busbars, welds, adhesive bonds, potting — are strained every time it heats and cools.

Thermal stress

Mechanical stress caused by a temperature change when a part cannot expand freely or is joined to a material that expands differently. A fully restrained aluminium bar warmed by 50 K would carry about 80 MPa. Repeated cycles fatigue welds, solder joints and adhesive bonds, which is what thermal shock testing sets out to provoke.

References & further reading

Further reading on this topic

These sources provide broader context; they are not presented as citations for every statement in this entry.

1. A General Energy Balance for Battery Systems

   Dawn Bernardi, Ellen Pawlikowski, John Newman · Journal of The Electrochemical Society · 1985

   Topic background · Battery energy balance and irreversible and reversible heat contributions. Reduced thermal models require explicit assumptions and current-sign conventions.

2. University Physics Volume 2, §1.6: Mechanisms of Heat Transfer

   OpenStax, Rice University

   Topic background · Conduction, convection, radiation and thermal resistance.