Thermal stress

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Busbar

A rigid copper or aluminium conductor that joins cell terminals into series and parallel groups, and modules into the pack. Its cross-section is sized for current and heating, and its joints — welded or bolted — are a classic source of resistance and failure.

Glass transition temperature

The temperature at which an amorphous polymer turns from hard and glassy to soft and rubbery, with a sharp fall in stiffness and rise in expansion. Adhesives, potting compounds and circuit boards are chosen with Tg clear of the operating range — standard FR-4 board is about 130–140 °C — so their joints are not loaded differently in service.

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 shock and cycling test

Moving a cell or pack rapidly between temperature extremes, typically −40 °C and +60 to +85 °C, for many cycles, to find seals, welds and housings that fail by differential expansion. It is in UN 38.3, R100 and most pack specifications.

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.