Formats

There are many different formats of battery cells, from button, cylindrical, prismatic and pouch. There are also a number of other formats and lots of sub-formats.

Button/Coin Cells

Mostly used in primary cells and available in a wide range of sizes for hearing aids, card readers and calculators.

In the chemistry research world coin cells are used for early testing of chemistry as they are small and simple to make in the lab. Therefore, it is possible to make and electrically test a large number of cells prior to moving to a larger format.

button or coin cell

Coin Pouch Cell

The active cell elements are circular and normally the same size as the coin cells. However, the case of the cell is a circular pouch. Thus giving the simplicity of the coin cell for making the active discs of material and the simplicity of a pouch cell in terms of sealing the elements into a shell.

cylindrical format cells

Cylindrical Cells

The 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.

The cylindrical format limits the packing density to at best hexagonal close pack.

Pouch Cells

They look like an aluminium jiffy bag with +ve and -ve terminals protruding from the edge.

They need to be supported mechanically and need a controlled pressure applied to the surface to deliver the power and energy over their lifetime.

A module will be required that can mechanically support the cells. This needs to maintain the required pressure, support electrical interconnections and manage the venting / failure of the cells in a controlled manner.

A strong thermal interface to the cell is difficult to design.

LG Chem pouch cell
prismatic cell

Prismatic Cells

As the name suggests these are a prismatic block, normally with the outer case made from aluminium. Again these come in many different formats and there is little standardisation apart from the VDA PHEV2 size of cell. These cells need a pressure applied to the main faces of the cell in order to maintain their performance over time.

blade cell format

Blade Cells

A derivation of the prismatic cell, but an important step as it enable the LFP EV pack by removing the overhead of the module.

First introduced by BYD, the blade format has been adopted by a number of manufacturers.

Redox Flow Battery

Redox flow batteries replace crystalline electrodes with energy-dense liquids that charge and discharge as they flow through the battery. This type of battery is well-suited for grid storage applications.

battery pack mass versus total energy in the pack for different cell formats

Cell Format and Pack Mass

The three main cell formats: Cylindrical, Prismatic and Pouch. There are pro’s and con’s with each. One of the most significant differences is the amount of mechanical support required.

The pouch cell needs the most support and fixing, followed by the prismatic and the most self contained mechanically is the cylindrical cell.

References

  1. Development perspectives for lithium-ion battery cell formats, Fraunhofer, November 2022