Cell formats

EV battery cells are commonly produced in three main formats: cylindrical, prismatic, and pouch. The format describes the cell’s external shape and enclosure, but it also influences manufacturing, cooling, mechanical support, electrical connections, and integration into the battery pack.

Cell format is separate from cell chemistry. NMC, NCA, LFP, LMFP, and sodium-ion describe electrochemical material systems, while cylindrical, prismatic, and pouch describe physical construction. A prismatic cell can use either NMC or LFP, and cells using similar chemistry can behave differently because their size, internal structure, terminals, cooling, and operating limits differ.

No format is best in every vehicle. Manufacturers choose between them based on production strategy, available pack space, structural design, cooling requirements, repair philosophy, cost, and the amount of energy contained in each cell.

External Format and Internal Construction

The external enclosure is only one part of cell design. The electrode sheets inside the enclosure also need to be arranged into a compact structure.

Two main assembly methods are used.

Wound Construction

In a wound cell, long sheets of positive electrode, separator, and negative electrode are layered and rolled into a spiral commonly called a jelly roll.

Cylindrical cells use a round jelly roll that fits inside the metal can. Prismatic cells can use a flattened wound structure, sometimes called a flat-wound or wound-prismatic design.

Winding is well suited to continuous, high-speed production because long electrode rolls can be processed without first cutting every layer into separate sheets.

The curved sections of a flattened roll can make less efficient use of the rectangular enclosure and create differences in mechanical pressure and current paths between the straight and curved parts.

Stacked Construction

In a stacked cell, separate electrode sheets or laminated electrode units are placed on top of one another with separator material between them.

Stacking can use the rectangular volume of a prismatic or pouch enclosure efficiently because the layers do not need curved ends. It also allows cell designers to control electrode alignment and pressure across the broad faces of the cell.

The process requires accurate cutting, positioning, inspection, and handling of many individual layers. Samsung SDI uses stacking in its prismatic cells, while LG Energy Solution uses lamination-and-stacking and Z-stacking processes for pouch cells. Pouch cells can also use wound structures, depending on the supplier and application. ([Samsung SDI Nyheter][1])

Cylindrical Cells

A cylindrical cell places a wound electrode roll inside a rigid cylindrical metal can. The positive and negative terminals are located at one or both ends, depending on the cell design.

The circular enclosure handles internal pressure efficiently and provides consistent mechanical support around the electrode roll. Cylindrical production also benefits from decades of automated manufacturing experience in consumer, industrial, and automotive batteries.

The shape does not fill a rectangular battery enclosure without gaps. However, these spaces are not necessarily wasted. Pack designers can use them for cooling channels, electrical insulation, structural adhesive, expansion clearance, or barriers intended to slow heat propagation.

Small and Large Cylindrical Cells

Cylindrical EV cells range from relatively small 18650 and 2170 cells to newer designs with a diameter of approximately 46 millimetres.

Smaller cells provide a large external surface area relative to the energy stored in each cell. This can help with heat transfer, and a fault in one cell involves less energy than a fault in a much larger cell.

The disadvantage is cell count. A large EV pack using small cylindrical cells may require several thousand cells, together with many welds, current paths, insulating components, and individual cell positions.

Larger cylindrical cells reduce the number of repeated components and electrical connections needed for the same pack capacity. Each cell contains more energy, however, increasing the importance of uniform cooling, current collection, manufacturing consistency, and protection against propagation to neighbouring cells.

Panasonic describes its 4680 cell as having approximately five times the capacity of its 2170 cell, allowing a pack of similar capacity to use fewer cells. Tesla continues to produce 4680 cells, including dry-electrode versions manufactured in Austin. ([energy.na.panasonic.com][2])

Terminal and Tab Design

The electrode foils inside the jelly roll need an electrical connection to the cell terminals.

Traditional cylindrical cells use one or more discrete tabs welded to the current collectors. Electrons must travel along the thin metal foil before reaching a tab, creating resistance and uneven current paths.

Newer cells can use:

• Multiple tabs distributed around the electrode
• Continuous-tab or tabless-style current collection
• Full-width current-collector connections
• Revised terminal positions intended to simplify pack assembly

Reducing the current-path length can lower electrical resistance and heat generation. The design must still be manufactured and welded consistently at very high production volumes. Tesla uses tabless manufacturing processes for its 4680 cell programme. ([Tesla][3])

Common Cylindrical Cell Sizes

Cylindrical names normally indicate approximate diameter and height. A 2170 or 21700 cell is approximately 21 millimetres in diameter and 70 millimetres high.

BMW’s Gen6 battery system uses 46-millimetre-diameter cells in different heights. The BMW iX3 uses a 95-millimetre-high version, while the BMW iX5 uses a 120-millimetre version. BMW states that the taller cell contains almost 30% more usable energy than its 95-millimetre cell. This refers to energy per cell, not a 30% increase in energy density, because the cell is physically larger. ([BMW Group PressClub][4])

Advantages of Cylindrical Cells

• Rigid and mechanically stable enclosure: The circular metal can supports the electrode roll and distributes internal pressure effectively.
• Mature high-volume production: Cylindrical cells are well suited to continuous and highly automated manufacturing.
• Consistent geometry: Standardised diameters and heights simplify handling, inspection, and production equipment.
• Large cooling surface with smaller cells: Small cells expose considerable can surface relative to their stored energy.
• Scalable cell sizes: Manufacturers can choose between many smaller cells and fewer large cylindrical cells.

Trade-Offs of Cylindrical Cells

• Gaps between cells: Round cells cannot completely fill a rectangular pack volume.
• High connection count with small cells: Packs may require thousands of cells and a large number of welds.
• More energy per fault with larger cells: Increasing cell size reduces cell count but raises the energy contained in each cell.
• Restricted geometry: Diameter, height, orientation, and terminal position influence the pack layout.
• Complex thermal balance: Cooling must remain consistent across the full jelly roll and between cells.

Prismatic Cells

A prismatic cell uses a rigid rectangular enclosure, normally made from aluminium or steel. The electrodes can be assembled as a flattened wound roll or as a stack of individual electrode layers.

The rectangular shape can use the available pack volume efficiently and allows a large battery to be built from relatively few cells. Broad cell surfaces also provide useful areas for cooling and controlled mechanical compression.

A large flat cell changes dimensions slightly as its state of charge, temperature, and age change. The battery pack must restrain this expansion without applying excessive local pressure to the cell.

Samsung SDI’s current prismatic designs use stacked electrodes inside a rigid aluminium enclosure. The company states that stacking avoids curved electrode regions and improves use of the internal can volume. ([Samsung SDI Nyheter][1])

Volkswagen Group Unified Cell

Volkswagen Group’s Unified Cell, developed by PowerCo, is a standardised prismatic cell platform intended for use across several vehicle brands, regions, suppliers, and battery chemistries.

It is not a separate cell format or one fixed chemistry. Volkswagen says the platform is designed to support NMC, LFP, sodium-ion, and potentially solid-state cell variants while retaining common external and manufacturing concepts.

The first PowerCo Unified Cell produced at the Salzgitter factory uses NMC chemistry. PowerCo states that LFP versions will follow. The Unified Cell is also designed to work with Volkswagen Group’s cell-to-pack battery architecture. ([Volkswagen Group][5])

Standardising the basic cell platform can reduce the number of unrelated components, production processes, and pack interfaces used across a large vehicle group. Internal details can still vary, including:

• Positive and negative electrode chemistry
• Electrode thickness and loading
• Electrolyte formulation
• Capacity
• Power and charging capability
• Usable voltage window
• Thermal requirements

The Unified Cell demonstrates why cell format should not be confused with chemistry. Two prismatic cells can use the same broad external platform while containing substantially different electrode materials.

Advantages of Prismatic Cells

• Efficient use of rectangular pack space: Cells can be placed closely together with little unused volume between them.
• Lower cell count: Large cells reduce the number of terminals, busbar connections, welds, and monitoring channels.
• Rigid enclosure: The metal can provides mechanical protection and simplifies cell handling.
• Broad cooling surfaces: The large faces or bottom surface can be connected to cooling plates.
• Platform-specific dimensions: Manufacturers can design cell size around the available vehicle floor and pack structure.
• Potential for standardisation within a manufacturer: Concepts such as Volkswagen’s Unified Cell can provide common interfaces across several vehicles.

Trade-Offs of Prismatic Cells

• Expansion management: Large flat faces need controlled compression throughout the cell’s life.
• Internal temperature gradients: A large cell can develop differences in temperature and state of charge across its width and thickness.
• High energy per cell: Failure of one large cell involves more stored energy than failure of one small cylindrical cell.
• Supplier-specific dimensions: There is no universal prismatic size family comparable to common cylindrical designations.
• Cooling consistency: Bottom or single-face cooling can create uneven temperatures if the internal design is not optimised.
• Mechanical stress around edges and terminals: Seals, corners, vents, and terminal assemblies require careful support.

Pouch Cells

A pouch cell uses a flexible laminated enclosure instead of a rigid metal can. The pouch film normally combines an aluminium barrier layer with polymer layers that provide electrical insulation, mechanical protection, and heat-sealable surfaces.

The electrode structure can be wound, stacked, laminated, or folded, depending on the design. Many automotive pouch cells use stacked or lamination-and-stacking processes to fill the rectangular enclosure efficiently.

During manufacturing, the electrode stack is inserted into the formed pouch, the leads are welded, electrolyte is added, and the pouch is sealed. A temporary gas pocket may be used during filling and formation before excess gas is removed and the pouch is given its final seal. ([BATTERY INSIDE][6])

The pouch enclosure uses less metal than a rigid can, reducing cell-level housing weight. It does not provide enough mechanical support by itself, so the surrounding battery structure must control pressure, protect the cell edges and seals, and maintain contact with the cooling system.

Pouch cells can expand because of normal electrode movement and can also swell if side reactions generate gas. Compression plates, frames, pads, and cooling surfaces are therefore part of the complete pouch-cell system rather than optional additions.

Advantages of Pouch Cells

• Low cell-enclosure weight: The laminated pouch is lighter than a rigid metal can.
• Efficient use of internal cell volume: A large proportion of the enclosure can be occupied by electrode material.
• Flexible dimensions: Manufacturers can produce wide, tall, thin, or otherwise platform-specific cells.
• Broad cooling surfaces: Large flat faces can provide good contact with cooling plates.
• Relatively low cell count: Large pouch cells reduce the number of electrical connections compared with packs using small cylindrical cells.
• Efficient stacked construction: Lamination and stacking can minimise unused space inside the pouch.

Trade-Offs of Pouch Cells

• Requires external mechanical support: The pack must provide compression, impact protection, and dimensional control.
• Sensitive edges and seals: Damage to the laminated film or lead seals can compromise the moisture barrier or containment.
• Swelling must be accommodated: Normal expansion and gas generation can affect pressure and cooling contact.
• More demanding handling: Large flexible cells can be difficult to position and assemble without bending or damage.
• Pack hardware offsets some cell-level weight savings: Frames, compression plates, pads, and protection structures add mass.
• Cooling contact depends on compression: Loss of contact between the pouch and cooling surface can create local temperature differences.

Long Prismatic and Blade-Style Cells

Blade-style cells are long, narrow prismatic cells designed to span a substantial section of the battery pack. They are not a fourth fundamental cell format.

BYD’s Blade Battery is the best-known implementation. It uses long, flat LFP prismatic cells arranged directly in the battery structure without conventional intermediate modules.

The cells are arranged so that they also contribute to the pack’s mechanical structure. The long shape provides a large external surface relative to cell thickness and can support efficient heat transfer.

Much of the claimed benefit comes from the relationship between the cell dimensions and the pack architecture, rather than from the cell shape alone. BYD describes the cells as long, flat units arranged directly into a module-free array, with later Cell-to-Body versions integrated into the vehicle structure. ([BYD][7])

The Blade Battery’s thermal behaviour also reflects its LFP chemistry and BYD’s specific cell and pack design. It should not be assumed that every long prismatic cell has the same safety, durability, or charging characteristics.

Advantages of Long Prismatic Cells

• Efficient pack integration: Long cells can reduce repeated module housings and intermediate structures.
• Large cooling surface relative to thickness: Heat has a relatively short path to the broad exterior surfaces.
• Structural contribution: The cells can act as beams or supporting elements inside the pack.
• Lower connection count: A pack can use relatively few large cells.
• Good use of pack width: Long cells can span much of the battery enclosure.

Trade-Offs of Long Prismatic Cells

• Closely tied to one pack geometry: Very long cells are difficult to reuse in vehicles with substantially different widths or floor layouts.
• Demanding dimensional control: Cell length, alignment, compression, and pack tolerances must be managed precisely.
• Large energy content per cell: Propagation protection remains important even when a thermally stable chemistry is used.
• Temperature and pressure variation: Conditions must remain consistent along the full length of the cell.
• Benefits depend on pack integration: A long cell does not automatically provide good structural or volumetric efficiency in a pack not designed around it.

Comparison of Cell Formats

The table describes broad tendencies rather than fixed performance rankings. Cell size, chemistry, electrode design, thermal management, and pack integration can change the result substantially.

Does Cell Format Matter to an EV Buyer?

Cell format is rarely a useful quality ranking on its own.

A vehicle does not automatically charge faster because it uses cylindrical cells, provide more range because it uses pouch cells, or last longer because it uses prismatic cells.

What the driver experiences depends on the complete battery system:

• Usable capacity
• Vehicle efficiency
• Charging curve
• Battery preconditioning
• Cooling and heating performance
• Cold-weather behaviour
• Battery degradation
• Warranty coverage
• Fault detection
• Protection against thermal propagation
• Pack repair strategy

Cell format helps explain why manufacturers choose a particular pack architecture. It also affects manufacturing cost, structural integration, and how failures may be diagnosed or repaired. The finished vehicle matters more than the shape of its individual cells.

The electrical arrangement and structural integration of these cells are covered in Battery Pack & Configuration.