There are three main types of lithium-ion batteries (li-ion): cylindrical cells, prismatic cells, and pouch cells. In the EV industry, the most promising developments revolve around cylindrical and prismatic cells. While the cylindrical battery format has been the most popular in recent years, several factors suggest that prismatic cells may take over.

What Are Prismatic Cells

A prismatic cell is a cell whose chemistry is enclosed in a rigid casing. Its rectangular shape allows efficiently stacking multiple units in a battery module. There are two types of prismatic cells: the electrode sheets inside the casing (anode, separator, cathode) are either stacked or rolled and flattened.

For the same volume, stacked prismatic cells can release more energy at once, offering better performance, whereas flattened prismatic cells contain more energy, offering more durability.

Prismatic cells are mainly used in energy storage systems and electric vehicles. Their larger size makes them bad candidates for smaller devices like e-bikes and cellphones. Therefore, they are better suited for energy-intensive applications.

What Are Cylindrical Cells

A cylindrical cell is a cell enclosed in a rigid cylinder can. Cylindrical cells are small and round, making it possible to stack them in devices of all sizes. Unlike other battery formats, their shape prevents swelling, an undesired phenomenon in batteries where gasses accumulate in the casing.

Cylindrical cells were first used in laptops, which contained between three and nine cells. They then gained in popularity when Tesla used them in its first electric vehicles (the Roadster and the Model S), which contained between 6,000 and 9,000 cells.

Cylindrical cells are also used in e-bikes, medical devices, and satellites. They are also essential in space exploration because of their shape; other cell formats would be deformed by the atmospheric pressure. The last Rover sent on Mars, for example, operates using cylindrical cells. The Formula E high-performance electric race cars use the exact same cells as the rover in their battery.

The Main Differences Between Prismatic and Cylindrical Cells

Shape is not the only thing that differentiates prismatic and cylindrical cells. Other important differences include their size, the number of electrical connections, and their power output.

Size

Prismatic cells are much larger than cylindrical cells and hence contain more energy per cell. To give a rough idea of the difference, a single prismatic cell can contain the same amount of energy as 20 to 100 cylindrical cells. The smaller size of cylindrical cells means they can be used for applications that require less power. As a result, they are used for a wider range of applications.

Connections

Because prismatic cells are larger than cylindrical cells, fewer cells are needed to achieve the same amount of energy. This means that for the same volume, batteries that use prismatic cells have fewer electrical connections that need to be welded. This is a major advantage for prismatic cells because there are fewer opportunities for manufacturing defects.

Power

Cylindrical cells may store less energy than prismatic cells, but they have more power. This means that cylindrical cells can discharge their energy faster than prismatic cells. The reason is that they have more connections per amp-hour (Ah). As a result, cylindrical cells are ideal for high-performance applications whereas prismatic cells are ideal to optimize energy efficiency.

Example of high-performance battery applications include Formula E race cars and the Ingenuity helicopter on Mars. Both require extreme performances in extreme environments.

Why Prismatic Cells Might Be Taking Over

The EV industry evolves quickly, and it’s uncertain whether prismatic cells or cylindrical cells will prevail. At the moment, cylindrical cells are more widespread in the EV industry, but there are reasons to think prismatic cells will gain in popularity.

First, prismatic cells offer an opportunity to drive down costs by diminishing the number of manufacturing steps. Their format makes it possible to manufacture larger cells, which reduces the number of electrical connections that need to be cleaned and welded.

Prismatic batteries are also the ideal format for the lithium-iron phosphate (LFP) chemistry, a mix of materials that are cheaper and more accessible. Unlike other chemistries, LFP batteries use resources that are everywhere on the planet. They do not require rare and expensive materials like nickel and cobalt that drive the cost of other cell types upward.

There are strong signals that LFP prismatic cells are emerging. In Asia, EV manufacturers already use LiFePO4 batteries, a type of LFP battery in the prismatic format. Tesla also stated that it has begun using prismatic batteries manufactured in China for the standard range versions of its cars.

The LFP chemistry has important downsides, however. For one, it contains less energy than other chemistries currently in use and, as such, can’t be used for high-performance vehicles like Formula 1 electric cars. In addition, battery management systems (BMS) have a hard time predicting the battery’s charge level.

You can watch this video to learn more about the LFP chemistry and why it is gaining in popularity.