Jelly roll (battery)

The jelly roll or Swiss roll design is the design used in the majority of cylindrical rechargeable batteries, including nickel–cadmium (Ni-Cd), nickel-metal hydride (Ni-MH), and lithium-ion (Li-ion). The design has this name because the cross section of the battery looks like a Swiss roll.

The inside of a Nickel-metal hydride battery, showing the jelly roll design:

1. positive terminal
2. outer metal casing (also negative terminal)
3. positive electrode
4. negative electrode with current collector (metal grid, connected to metal casing)
5. separator (between electrodes)

In this design, an insulating sheet is laid down, then a thin layer of an anode material is laid down, a separator layer is applied, and a cathode material is layered on top. This sandwich is then rolled up and inserted into a hollow cylinder casing. The battery is sealed, metal contacts are attached, and an optional button top is applied if the battery is intended to replace an AAA/AA/C/D alkaline battery. A label with the brand name is then applied, or a blank protective label, often green (for Ni-MH) or blue (for Ni-Cd) for a generic or OEM battery.

Occasionally, the design is also used for primary (non-rechargeable) batteries, like lithium iron disulfide (Li-FeS2) patented by Energizer, although most common primary batteries use the conventional rod-paste-tube design, like the zinc-carbon and its successor the alkaline battery.

The Swiss roll design is likewise used for the plates of cylindrical capacitors.