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Battery Management Systems for Large Lithium-Ion Battery Packs

Section 1.2 Addenda

Cell expansion

There are two mechanisms that result in cell expansion:

Note that that second mechanism of expansion only occurs when the STATE of the cell is around 100 % SOC. This point is very important. The expansion is NOT due to heat, and it is NOT due to the act of charging. The expansion is the same regardless of cell temperature (cooling won't prevent the expansion) and cell current (at a given SOC level, the expansion is the same, regardless of whether the cell is charging, discharging or sitting on a shelf).

Cylindrical cells will inherently contain that expansion. Pouch cells won't do so, so they must be contained. Prismatic cells will contain expansion to a small extent, so they too need to be contained. How much containment is required is up for debate, and I discuss it in the addenda to section 6.1.1.3.2. The jest of it is that you need to allow for some expansion (for mechanism 1) , but not too much (for mechanism 2), and the answer depends on the particular model of cell.

book/1.2.add (last edited 2010-12-12 16:09:50 by DavideAndrea)