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.

Home » Cell » Formats » Cylindrical Cells » 21700 Cylindrical Cells
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.

21700 cell sizes

The 21700 cell by definition should be 21mm in diameter and 70mm high.

Clearly the cell sizes are quite variable.

Plotting the volume lines onto this shows that the cells have a trendline of increasing diameter and hencing increasing the volume by up to 10%.

21700 cell size and volume lines