Prismatic Cells vs. Cylindrical Cells: What is the Difference?

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.

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Because Laserax provides laser solutions for battery manufacturing, we are watching these developments closely. Before we go over what’s coming, let’s do a quick overview of the two types of batteries.

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. 

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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. 

Most primatic LFP cells are thick electrode design. Thick electrode means the thickness of graphite negative electrode and positve LFP electrode are 110 to 150 um thick. This yields the most AH capacity per unit volume and weight but cell suffers from ion starvation above about 0.5CA cell current caused by the thick electrodes. This increases terminal voltage slump and internal cell heating accelerates above 0.5 CA cell current.

Most cyclindical cells are made with thinner electrodes design in 50 um to 100 um thickness. This means more layers are required for same AH rating as capacity is dependent on amount of graphite and LFP material. More layers mean more copper foil, aluminum foil, and electrolyte. This costs more, takes up volume, and adds weight. Extra metal foil benefits are lower contact resistance and better heat dissipation. Cylindrical cell with thin electrode allow high peak cell current with onset of electrode layer ion starvation at a much higher current. This also helps at cold temps where ion migration rate slows down.

Prismatic cells with thick electrode design.
+ Most capacity per unit volume and weight
+ lowest cost
- lower peak discharge current
- less ability to dissipate internal cell heating

Cylindrical cells with thin to moderate electrode design
+ higher peak current discharge rate
+ ability to dissipate internal heating
+ better cold temp performance
- AH per volume/weight
- higher cost

There is really no difference in damaging effects of, depth of discharge between thin or thick electrode designs. Both will grow metal dendrites if left for moderate time below 1.0 vdc and both will have severe electrolyte decomposition if discharged below about 0.1 vdc or charged above 4.3 vdc.

Are you interested in learning more about cylindrical vs prismatic cells? Contact us today to secure an expert consultation!