Composite copper foil current collectors with sandwich structure for high-energy density and safe lithium-ion batteries

Lithium-ion battery is an efficient energy storage device and have been widely used in mobile electronic devices and electric vehicles. As an indispensable component in lithium-ion batteries (LIBs), copper foil current collector shoulders the important task of collecting current and supporting active materials, and plays a pivotal role in promoting the development of high-performance lithium-ion batteries. Compared with traditional electrolytic copper foil, composite copper foil with a distinctive "Cu-polymer-Cu" sandwich structure significantly reduces the weight of current collector and increases the energy density of battery. In addition, the transverse insulated and flexible polymer interlayer can block heat diffusion and alleviate the expansion stress. Therefore, the safety and cycle performance of lithium-ion battery can be improved. In this review, the requirements of copper foil collectors, the characteristics of polymer interlayer, the advantages of composite copper foil and the preparation methods of composite copper foil are introduced. Aiming at the weak bonding force between copper and polymer in composite copper foil, the improved methods to enlarge the bonding force are summarized. With the emphasis on the key perspectives, the paper will provide valuable inspiration for the rapid development of composite copper foil to advance high-energy density lithium-ion batteries.