A lithium-ion pouch cell stores energy in thin layers sealed in a foil bag. Use the buttons to look inside, then follow the lithium ions and electrons that carry the charge.
A pouch cell is one common shape of lithium-ion battery. Rather than a rigid cylindrical or prismatic can, its layered stack is sealed inside a thin, flexible foil pouch, with two metal tabs for the terminals. Its flat, light form suits phones, tablets and slim battery packs.
A pouch cell is just a sealed silver bag from outside. Everything that stores and moves the charge — the layered electrodes, the separators, the electrolyte — is hidden inside, so cutting it open shows how such a thin package holds so much energy.
A charged cell holds lithium ions tucked into the grey graphite anode. The layers stack the electrodes close together, so the ions never have far to travel and the cell can deliver a large current.
When an external circuit is connected, lithium leaves the graphite anode as positive ions. At the same time, electrons are freed from the anode and start to flow out through the metal current collector and the negative tab.
The lithium ions travel through the liquid electrolyte and pass through the porous separator. The separator lets the ions through but blocks the electrons, forcing them to make the trip around the outside circuit instead.
The ions arrive at the blue cathode of lithium metal oxide and slip into its structure. There they are rejoined by the electrons that travelled around the external circuit, completing the reaction.
The stream of electrons running from the negative tab, through the load, and back to the positive tab is the current the cell delivers. Charging pushes the whole process into reverse.
Its container. Instead of a rigid metal can, the stack is sealed inside a thin, flexible foil pouch. That makes the cell lighter and lets it be made in flat shapes that pack neatly into phones, tablets and battery packs.
Each cathode-separator-anode set is one thin cell, and the sheet area sets how much current it can give. Stacking many of them, or rolling them up, packs a large active area into a small volume.
The liquid electrolyte soaks every layer and carries lithium ions between the electrodes. Without it, ions could not cross the separator, and the cell could not work.
It is the safety barrier. It lets lithium ions pass but must block electrons, and it keeps the two electrodes from ever touching. A separator failure is what leads to a short circuit.
Because the foil pouch is flexible, the cell can swell as it ages and needs to be held under gentle pressure inside its pack. A rigid metal can holds its shape on its own.