The smallest working unit in a battery is the electrochemical cell, consisting of a cathode and an anode separated and connected by an electrolyte. The electrolyte conducts ions but is an insulator to electrons. In a charged state, the anode contains a high concentration of intercalated lithium while the cathode is depleted of lithium. During the discharge, a lithium ion leaves the anode and migrates through the electrolyte to the cathode while its associated electron is collected by the current collector to be used to power an electric device .
The cell designs and combinations in modules and packs differ greatly. To establish a base understanding, this paper shows the main cell designs and then focuses on materials, processing, and manufacturing with special emphasis on batteries for transportation.
The electrodes in lithium-ion cells are always solid materials. One can distinguish between cell types according to their electrolytes, which may be liquid, gel, or solid-state components. The electrolytes in gel and solid-state cells represent a structural component and do not need additional separators for the effective separation of electrodes and avoidance of short circuits. Cells come in button, cylindrical, and prismatic forms .
For low-energy and low-power applications, a cell often represents a full battery. For high-energy and high-power applications such as transportation or stationary storage, a number of cells are packaged in a module, and a number of modules are packaged in a battery.