How are the prismatic cells used in lithium-ion batteries made?

They have a generous size and are used in storage systems and electric cars. In the future, they could be the most widely used.

cellule prismatique northvolt

By: Francesco Barontini

Published by: Brian Potter

Dec 27, 2023 at 4:12am ET

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Lithium-ion battery cells come in a variety of shapes. Initially, the focus was on the cylindrical format, but recently, bag-shaped cells and prismatic cells have also appeared.

Prismatic cells in particular, as well as cylindrical cells, seem to be the most promising developments. Indeed, although the 4680 from Tesla, BMW and others seems to be leading cylindrical cells into a bright future, it is the prismatic cells that many analysts believe could ultimately come out on top.

How they work

Let's start with how they work: prismatic cells, like cylindrical cells, are lithium-ion cells and therefore use two electrodes, a separator and an electrolyte.

More specifically, they have an anode (negative electrode), made of graphite or silicon, and a cathode (positive electrode), made of lithium metal oxide to which various other elements such as nickel, manganese and cobalt are added. They are separated by a separator, usually made of plastic.

The electrodes and separator are made of foil and are then immersed in an electrolyte (almost always a liquid) that allows the electrodes to move in either direction, depending on whether energy is being stored or transferred.

A prismatic cell with rolled leaves

Two types of prismatic cells

Prismatic cells, like the others, are cells in which the active component is enclosed in a rigid envelope. Their advantage over cylindrical cells is in terms of space management within the battery pack itself: thanks to their rectangular shape, they can be placed next to each other with minimal bulk.

There are two types of prismatic cells: those in which the sheets of electrodes and separators are stacked on top of each other, and those in which they are rolled on themselves and then flattened. For the same volume, stacked-foil prismatic cells can release more energy at the same time, offering better performance, while flattened-foil prismatic cells contain more energy, offering a longer service life.

Stacked-foil prismatic cells: enhanced performance
Laminated and flattened prismatic cells: longer service life

CATL al Salone di Shanghai

CATL prismatic cell with nickel-manganese-cobalt chemistry

Where are they used?

Prismatic cells are generally large. The fact that they are bulky (the long side can exceed 20 cm) means that they are mainly suitable for stationary energy storage systems and electric vehicles.

Why might these cells take over?

As we mentioned, cylindrical cells are currently the most popular in electric cars. But things are changing, mainly for two reasons.

The first is that they are produced by simpler processes and are therefore generally less expensive. In addition, because they are larger, there are fewer of them in a battery pack, which simplifies connections, accessories and electrical wiring.
Secondly, these are the lithium-iron-phosphate batteries most widely used today. This is a rapidly developing chemistry, which reduces costs still further thanks to cheaper and more readily available raw materials and, thanks to recent advances, narrows the performance gap with lithium-ion batteries using traditional chemistry.

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