The cylindrical, prismatic, and pouch cells have different form factors, energy densities, and weights. Therefore, their use cases in electric vehicles (EVs) differ depending on the applications. This article will compare the three parameters of the three battery geometry types with necessary facts and figures. We’ll conclude how the parameters of each battery type can be optimized for EV battery packs.
Figure 1 illustrates the cylindrical, prismatic, and pouch cells, along with their geometry and dimensions. Although the geometries differ, all batteries consist of a positive electrode, a negative electrode, a separator, and a case. However, how these parts are constructed differently across the three cell types affects their use in EV battery packs.
Figure 1. The commonly used battery cell types: cylindrical cell, prismatic cell, and pouch cell. (Image: Ufine Battery)
Form factor comparison of the cells
The cylindrical cells are available in standard sizes, such as 18650 (18 mm diameter, 65 mm length) and 21700 (21 mm diameter, 70 mm length). They have limited system-level flexibility compared to prismatic and pouch cells, as they leave gaps between the cells when stacked during the manufacture of EV battery packs. However, these gaps can be advantageous for cooling when liquid coolants can be circulated through the gaps.
The prismatic cells are flat, rectangular, or square-shaped and usually larger than cylindrical cells. They have better space efficiency than cylindrical cells because they do not leave gaps. However, this can be a problem, as there is no room for expansion if the cell heats up.
Pouch cells have the most adaptable form factor because they do not have a rigid casing, unlike the other two cells. They have the highest packaging efficiency because of their pouch-like flexible structure. They can easily fit into available spaces and unconventional spaces. However, care should be taken to account for possible swelling, considering proper space design in case of thermal expansion.
Figure 2 compares the three battery geometry types based on capacity (kWh) and volume (L). It can be concluded that the prismatic cell occupies a larger volume (458 L) for a capacity of 82 kWh among the three. The commonly used 2170 Panasonic (cylindrical) and Ultium GM (pouch) batteries occupy a lower volume, while their next-generation counterparts, the 4680 Panasonic (cylindrical) and Licerion Sion (pouch) batteries, occupy even lesser volumes of 325 L and 307 L, respectively.
Figure 2. Capacity and total battery volume comparison of cylindrical, prismatic, and pouch cells of five battery models. (Image: Latin American Journal of Energy Research)
It’s also worth noting that the capacity of the 4680 Panasonic and Licerion Sion batteries has increased by 23% and 27.2%, respectively, over their earlier generations.
Energy density comparison of the cells
The energy densities of cylindrical, prismatic, and pouch batteries can be better understood at the cell and system levels. At the cell level, the energy density depends on the battery chemistry. However, at the system level, the energy density depends on how efficiently the batteries occupy the space in the battery pack. The chart in Figure 3 compares the cell- and system-level energy densities of cylindrical, prismatic, and pouch batteries.
Figure 3. The energy density of cylindrical, prismatic, and pouch-bag modules at the cell level (blue) and system level (orange). (Image: World Electric Vehicle Journal, MDPI)
Weight comparison of the cells
Pouch cells are typically the lightest option among the three types, making them ideal for applications where weight reduction is important. Cylindrical cells have a moderate weight, influenced by their metal casing, but are generally lighter than prismatic cells. Prismatic cells are the heaviest, especially in larger formats designed for high-capacity applications like EVs.
Figure 4 shows a graph comparing the total battery weight of cylindrical, prismatic, and pouch cells. The prismatic cell from Samsung SDI weighs 575 kg for a 120 Ah capacity. The commonly used 2170 Panasonic (cylindrical) and Ultium GM (pouch) types weigh lower at 530 and 510 kg, respectively. However, the newer generation cylindrical 4680 Panasonic (cylindrical) and Licerion Sion (pouch) cells weigh 166 and 163 kg less, respectively, than their older generation.
Figure 4. The capacity and total battery weight comparison of cylindrical, prismatic, and pouch cells of five battery models. (Image: Latin American Journal of Energy Research)
Regarding capacity, the next-generation 4680 Panasonic and Licerion Sion cells are effective at increasing capacity by 45.5 and 47.1%, respectively, compared to their earlier-generation counterparts.
Optimizing battery packs based on the cells
Having compared the form factor, energy density, and weight of the three battery types, and based on extensive research conducted by a team of researchers from the Institut Teknologi Bandung and the National Center for Sustainable Transportation Technology, Bandung, Indonesia, we present the following optimization of EV battery packs based on battery geometry.
Cylindrical cells have a better overall advantage over the other two types due to their higher energy density at the cell level and the stronger mechanical support provided by the metal casing surrounding the battery. Therefore, the battery can be placed at the bottom of the vehicle to bear the increased stress during driving and save space in EVs.
The prismatic cell offers a competitive energy density at the system level, but it may undergo high stress at the corner of the bending cell due to its packaging process. However, they have a better packaging density, leading to a higher output power, which is particularly useful in high-power EVs. Pouch cells possess the necessary energy density for EVs, but their mechanical integrity remains a question. At this point, they can be used in applications that require low power within EVs, especially as auxiliary power.
Summary
Cylindrical cells have traditionally found extensive application in EVs due to their strong mechanical support provided by the metal casing, even though their energy density at the system level decreases compared to that at the cell level.
The prismatic cells have a higher manufacturing cost due to their specialized design, and they are well-suited for EV battery packs with specialized packaging designs. Pouch cells have poor thermal conductivity but are highly adaptable, requiring fewer materials and steps in their manufacturing. They are suitable for powering EV accessories that require less power than the EV motor.
References
- From Cell to Battery System in BEVs: Analysis of System Packing Efficiency and Cell Types, World Electric Vehicle Journal, MDPI
- A comparative study of different battery geometries used in electric vehicles, Latin American Journal of Energy Research
- Battery Cells for Electric Vehicles, International Journal of Sustainable Transportation Technology
- Comparatively assessing different shapes of lithium-ion battery cells, Procedia Manufacturing, Elsevier
- Prismatic vs Pouch vs Cylindrical Lithium Ion Battery Cell, Grepow Battery Co.
- Cylindrical, Prismatic, or Pouch Cell: A Complete Comparison, Ufine Battery
- Prismatic vs Cylindrical Battery Cells: What’s the Difference?, Holo Battery
Images
- Figure 1, Ufine Battery
- Figure 2, Latin American Journal of Energy Research
- Figure 3, World Electric Vehicle Journal, MDPI
- Figure 4, Latin American Journal of Energy Research
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Filed Under: Batteries, FAQs