(Invited) Characteristics, Types and Development Direction of the Copper Foils for Batteries

Abstract

Copper foil with low electrical resistivity was originally developed as an improved interconnect material for printed circuit boards. Since the development of lithium-ion batteries in the 1990s, copper foil has been used as anode current collectors in secondary batteries. The control of copper electroplating conditions is a vital factor in the manufacturing of such copper foils. The manufacturing process comprises plating on a drum, surface treatment, and slitting. In particular, the core process of copper electroplating is the control of the additive recipe in copper electroplating. KCFT (Korea Copper Foil and FCCL Technologies) in South Korea is one of the leading companies in the world to develop these technologies. Copper foil has the characteristics of double-sided shine. Since it is generally coated on both sides, the characteristics of both sides should be similar. For batteries, an anode is fabricated by coating an active material, such as natural or artificial graphite, on a copper foil. Batteries may be of the cylindrical, prismatic, or pouch types. The cylindrical-type battery is manufactured as a jelly roll, and the pouch-type battery is usually made by laminating. Depending on the properties of the copper foils, they can be classified as follows: general, high-strength, high-elongation, and high-strength and high-elongation types. The desired copper foil properties can be realized by controlling the grain size and its growth inhibition during heat treatment. The direction of development for the copper foils for batteries is first to manufacture thin copper foil. The capacity or weight of the thin copper foils can be enhanced or reduced, respectively. Second, the stable handling of the battery manufacturing process should be realized. Third, the copper foil productivity will be improved by adopting high-current-density plating or manufacturing longer and wider products. Finally, in order to improve the reliability of the batteries, copper foil swelling and breakage should be prevented by using high-strength materials and high-elongation materials for cylindrical-type batteries. In conclusion, there is the need to develop of copper foil well based on the understanding of the role of additive and the understanding of the metal structures.