Synthesis of silicon anode binders with ultra-high content of catechol groups and the effect of molecular weight on battery performance

Highly adhesive binders are developed to prolong the cycle life of silicon anodes and accelerate their practical application. A series of poly(N-methacryloyl-3,4-dihydroxy-L-phenylalanine) (PMDOPA) binders, containing ultra-high content of catechol groups, are synthesized through radical polymerization and applied to silicon anodes. The ultra-high content of catechol groups endows the PMDOPA binder superior adhesive strength compared to the carboxyl groups of the polyacrylic acid (PAA) binder. As the molecular weight increases, the flexibility, solvent resistance and adhesive strength of the PMDOPA binders are all enhanced, which effectively alleviates the electrode pulverization during long-term cycling and prolongs the cycle life of batteries. Especially, the PMDOPA-20 binder, which possesses the highest molecular weight of 208 kDa among all the PMDOPA samples, exhibits the longest cycle life of 665 cycles at the current density of 840 mA g, even though its molecular weight is lower than PAA. This work demonstrates that both the functional adhesive group and molecular weight are crucial for binder performance, which provides a valuable reference for the future development of high-performance binders.