The Influence of Surface Morphology of Copper Foils on the Efficiency of Lithium Ion Batteries

Abstract

For the increasing demand of portable electronic devices and electric vehicles, lithium-ion batteries (LIBs) become a fast-growing and crucial technology because of high power density and light weight. To manufacture LIBs with good performance and appropriate cost, the components constituting LIBs should not only possess excellent quality and reliability but also be cost-effective. The current collector in the negative electrode of LIBs is an indispensable material, and the most commonly used material is copper foil with optimal quality. Currently, the mainstream copper foil adopted in LIBs is manufactured by rolling, since the rolled copper foil provides smooth surfaces on double sides (Rz < 1 μm), which ensure good capacity retention rate. However, the rolled copper foil is much more expensive than electrodeposited (ED) copper foil, especially for ultra-thin one (< 8 μm), since it requires more times of rolling and annealing. Consequently, the manufacture of thin ED copper foil with optimal properties is a critical issue to lower the cost of LIBs. Unfortunately, the ED copper foil produced by conventional method is not applicable in LIBs industry, and the main reason is that the surface roughness of the ED copper foil on both sides is remarkably different, which affects the capacity retention rate of LIBs [1]. In addition, the actual mechanism of how the surface morphology influencing the performance of LIBs has been not studied yet. In this work, we produced an 8 μm thick ED copper foil with different surface morphology by adding specific additives in the plating bath, including very low profile copper foil (Rz < 0.1 μm) or copper foil with pinholes on the surface, and comparing the performance of these ED copper foils with a conventional ED copper foil and a commercial rolled copper foil. The surface morphology and structure of each copper foil was examined by SEM, AFM, and XRD. Most importantly, carbon based material would be coated on these copper foils and then sealed in coin cells to examine the electrochemical behavior and efficiency of lithium ion coin cells. Accordingly, the relationship of the active carbon material and the surface morphology of the negative current collector was clarified. Reference : 1. Kazuo Kondo, Rohan N. Akolkar, Dale P. Barkey, Masayuki Yokoi, Copper Electrodeposition for Nanofabrication of Electronics Devices, p. 243, Springer-Verlag New York (2014).