Current Collector
A current collector is the electrically conductive substrate that carries electrons between a battery's porous electrode coating and its terminals. In conventional lithium-ion cells it is usually thin metal foil, but it is not the active electrode material that stores and releases ions. DOE Energy Storage Handbook: Lithium-Ion Batteries
Common construction
Copper foil is commonly used on the negative-electrode side and aluminum foil on the positive-electrode side because each must remain stable within that electrode's operating potential. This pairing is common, not universal: lithium-titanate negative electrodes can use aluminum, and alternative metal-coated polymer collectors are under development. Oak Ridge National Laboratory: Lightweight current collectors for EV batteries
The collector adds little or no electrochemical storage of its own, yet its conductivity, thickness, surface adhesion, mechanical strength, and connection to tabs affect resistance, manufacturability, mass, and reliability. The active-material coating, binder, and conductive additives together form the practical electrode on its surface.
For the deeper component and electrode interactions, see Cell Chemistry & Components.