Inside Panasonic NCR18650 Lithium-Ion battery cell

Cristian Miuta, Jan 30, 2018.

The metal case holds a long spiral comprising three thin sheets pressed together: a positive electrode, a negative electrode, and separator. Inside the metal case, these sheets are submerged in an organic solvent that acts as the electrolyte – Ethylene Carbonate, Diethyl Carbonate and Lithium Hexafluorophosphate (salt).

 

The separator is a very thin sheet of microperforated plastic. As the name implies, it separates the positive and negative electrodes while allowing ions to pass through.
A copper foil is used for anode current collectors due to its workability and electrical conductivity.

The positive electrode is made of Lithium Cobalt Nickel Aluminum Oxide or LiCoNiAlO2.
The negative electrode is made of carbon (graphite). When the battery charges, ions of lithium move through the electrolyte from the positive electrode to the negative electrode and attach to the carbon. During discharge, the lithium ions move back to the LiCoNiAlO2 from the carbon.

Also inside is a PTC (Positive Temperature Coefficient) mechanical switch, a device that keeps the battery away from overheating.