High strength Cu foil without self-annealing prepared by 2M5S-PEG-SPS

Cu foil has widely been used as a current collector for Li ion batteries due to its excellent electrical, mechanical properties and facile fabrication process, but improvement in the properties of Cu foil is necessary for continuous development of the Li ion battery. Thinner and stronger Cu foil is being demanded, and the self-annealing of Cu foil needs to be prevented for effective control of properties as well as higher productivity of the fabrication process. We investigated the effects of three additives, 2-mercapto-5-benzimidazole sulfonic acid (2M5S), polyethylene glycol (PEG), and bis (3-sulfopropyl) disulfide (SPS), on the mechanical properties and self-annealing phenomenon of Cufoil. Cu foil deposited with PEG shows the highest tensile strength and elongation after electrodeposition; however, it experiences severe self-annealing for 48 hrs. On the contrary, 2M5S and SPS reduce the self-annealing phenomenon with their incorporation into Cu film, while the initial mechanical properties are worse than those with PEG. Therefore, combinations of additives are investigated to obtain both higher mechanical properties and excellent resistance against self-annealing. Finally, 10 µm-thick Cu foil having a tensile strength of 673 MPa and an elongation of 2.9% without self-annealing can be fabricated using PEG-2M5S-SPS.