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Li-Ion batteries come in four basic shapes: pouch, prismatic, and cylindrical (small and large). Some of these formats are simpler to work with than others, which makes them better suited for specific projects.
Cylindrical -
Lithium-ion batteries were most frequently seen in small-format (less than 5 Ah) cylindrical cells. The 18650 (18-mm diameter and 65-mm length) and the 26650 are the two most popular standard sizes (26-mm diameter and 65 mm in length).
The cell's negative terminal typically occupies the majority of the can-shaped cage, with the positive terminal and vent located at one end. A single "jelly-roll" of electrodes and a separator are used in cylindrical cells.
Prismatic -
Prismatic cells provide a sturdy, rectangular-shaped iron cage. After assembly but before electrolyte filling, the enclosure is typically sealed using laser welding.
The maximum packing factor for cylindrical cells is approximately 90%. In contrast, prismatic cells have a more comprehensive range of sizes and forms and can be packed more densely. Manufacturers may have different vent and terminal placements.
Pouch -
A pouch containing pouch cells is assembled by joining two pieces of plastic film together at the edges. For connecting to the cell, metallic tabs protrude from the pouch. The direction in which the lithium ions migrate in pouch cells is often fairly flat.
The electrode and separator can be wrapped, folded, stacked, or placed into prismatic or pouch cells. Cells in pouches often vent at the pouch's sealed edge.