21700 cells and monomers

What is a 21700 cell?

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. The 21700 cell increased the working volume over the 18650 by a factor of >1.4x 21700 => ~21mm in diameter and ~70.0mm long

What is a 21700 battery?

They were made in a joint effort between Panasonic and Tesla. The 21700 battery cell has a dimension of 21mm diameter and 70mm in length. The cells are slightly larger than the 18650 and have a higher capacity. These cells have the same nominal capacity of the batteries they were designed to replace, as they still came as 3.6 volts to 3.7 volts.

What makes the 21700 Li-ion cell new?

The 21700 Li-ion cell is a new format compared to the classic 18650 format. Both types of cells were reproducibly built on pilot scale with the same electrodes, separator, and electrolyte allowing a direct comparison for the first time.

What is the difference between 18650 and 21700 cells?

The main differences between 18650 and 21700 Li-ion cells include electrolyte amounts (5 mL vs. 7 mL) and positive terminal resistance (higher in 18650). Other aspects like electrolyte composition, separator type, housing materials, and wall thicknesses are the same for both formats.

How to increase cycle life in cylindrical 21700 cells?

Our group 26, 27 demonstrated experimentally an increased cycle life in cylindrical 21700 cells, by changing the welded tab design with only a few single tabs to a foil tab design. Using advanced charging strategies is another way to reduce the charging time.

What is the separator used in both 18650 and 21700 cells?

The separator used in both 18650 and 21700 cells is Celgard H1609. The electrolyte amounts (1 M LiPF 6 in EC : EMC = 3 : 7 (wt.-%) + 2% VC) were 5 mL and 7 mL in the 18650 and 21700 cells, respectively.