Types of Cells

Cylindrical

• Sheet-like anodes, separators, and cathodes that are put together, rolled up, and packed into a cylinder-shaped can.

• the round shape of the battery distributes the internal pressure from side reactions over the cell circumference almost evenly, allowing for the cell to tolerate a higher level of internal pressure without deformation. (Check this out for clarification: Internal Pressure - an overview | ScienceDirect Topics)

• Has high mechanical stability, and is used in optimized automation processes and techniques, increasing consistency and lowering the cost per unit.

DISADVANTAGE due to its shape, we cannot fully utilize the space available in the battery pack, leading to the lower packing density of the cylindrical cell.

• But, thermal management of a pack of cylindrical cells is easier since the space cavities let the coolant easily circulate around the cells within a battery pack.

Why Tesla uses Cylindrical Cells

• Have longevity, relatively cheap price point, and comparatively low watt-per-hour cost

• May be more beneficial to use a larger amount of cylindrical cells than a relatively smaller amount of prismatic cells in the same pack, since they are connected in series and the former will be less affected if one/few cell malfunctions

Prismatic

• Consist of large sheets of anodes, cathodes, and separators put together, rolled up, and pressed into a metallic/hard-plastic housing in cubic form. 

• Placing the electrode/separators close to the corners of the containers may cause stress and lead to non-uniform distribution of the electrolyte

• Easier to optimize the available space, but suffers from tricker thermal management due to lack of space cavities (opposite of cylindrical, pretty much)

• Swell less than pouch cells, but not as mechanically stable as cylindrical

• Modern prismatic cells are used in the electric powertrain and energy storage systems.

Pouch

• Container is a sealed flexible foil, and not rigid, leading to reduction in weight and easy fit.

• Swelling can occur (expect around 8% to 10% after 500 charge/discharge cycles)

• Obviously don’t place near sharp edges, and use some sort of a support structure (hard case)

Why laptops use pouch cells?

• Very efficient use of space, and are of flexible size

• safety performance is good, since a when a problem occurs, it may will bulge/swell up and crack, but will not explode/ cause a fire since gas cannot be released (unlike a shell, which will explode)

• small internal resistance, smaller/equal in size than prismatic/cylinder, but higher energy density