21700 Cylindrical Cells

The active layers of the cell are wound in a spiral. Normally these cells have the lower case as the negative terminal and the top centre as the positive terminal. However, a number of larger cylindrical cells have both +ve and -ve terminals on the top surface.

For this article we will concentrate on the 21700 format, but this is migrating towards the 46mm diameter 46xx class of cylindrical cells in a push to reduce cell manufacturing costs.

18650 and 21700 cylindrical cell drawings

The 21700 cell increased the working volume over the 18650 by a factor of >1.4x

21700 => ~21mm in diameter and ~70.0mm long

These dimensions vary between manufacturers.

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mass distribution of 21700 cells

Using data from the Cell Database we can see that 70g is a good nominal figure for the mass of a 21700 cell.