Elucidation of the Adhesion Mechanism for PVDF-Based Binders on the Current Collector of the Cathode in Lithium-Ion Batteries
Keisuke Watanabe, D. S. Tomar, Kosuke Ikuno, Hibiki Tsunekawa, Ken‐ichi Inoue, Shen Ye
Abstract
In lithium-ion batteries (LIBs), adhesive binders play a crucial role in maintaining the stability of electrode materials on substrate surfaces during long-term practical operation. Polyvinylidene fluoride (PVDF) is the most widely used among these binders. To improve the adhesion properties of PVDF to the aluminum (Al) current collector of the cathode of LIBs, we designed a structure-modified PVDF copolymer by polymerizing vinylidene fluoride monomer with a small content of carboxyethyl acrylate (CEA) monomer under different synthesis conditions. The resulting copolymers exhibit significantly improved peel strength to the Al current collector compared to conventional PVDF. Structural analysis of the synthesized copolymers reveals substantial differences in the CEA monomer sequence structures predicted by random ratio values of nuclear magnetic resonance (NMR) results. A surface-sensitive sum frequency generation (SFG) vibrational spectroscopy study revealed a specific hydrogen (H) bonding interaction between the CEA units in the copolymer and the Al interface, contributing to enhanced polymer adhesion. Furthermore, we found that the uniformity in the sequence of CEA units in the copolymer chain leads to a unique segregation and distribution of the CEA units in the interfacial region of the Al substrate, which helps improve the adhesion further. Based on our findings from NMR, SFG, infrared spectroscopy, and gel permeation chromatography measurements, we propose a mechanism for the adhesion of PVDF-based binders to Al surfaces. This research provides valuable insights for understanding and controlling adhesion behaviors on the electrode substrate surface used in energy storage devices.