Prismatic Cells vs. Cylindrical Cells: What is the Difference?
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.
Prismatic Cells in Energy Storage Systems
When it comes to battery pack production demand, energy storage systems (ESS) are just as important as electric vehicles. ESSs are already using prismatic cells and it is very likely that they will keep using them. Prismatic cells have a longer cycle life, are less dangerous, and come at a low cost compared to cylindrical cells.
The Switch to Prismatic Batteries
With its tabless cell design, high energy density, and low manufacturing cost, Tesla’s 4680 cylindrical cell is probably the most noteworthy battery cell at the moment. But recently, Elon Musk has talked about the advantages of prismatic cells, and Tesla has begun using them in certain car models.
The 4680 cylindrical cells haven’t been replaced by prismatic cells yet, but Tesla’s next move will be telling of what the future holds. Will they replace the 4680’s Nickel-Cobalt-Aluminum oxide (NCA) chemistry with the LFP chemistry? If so, will they switch to prismatic cells, the preferred format for this chemistry? With the increased cost of raw materials around the world, it is a strong possibility.
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Cylindrical vs Prismatic Cells
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.
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