A covalent organic framework-modified polyacrylic acid binder enhances the cycling performance of silicon–carbon anodes

Abstract

Silicon is considered an ideal anode material for next-generation lithium-ion and solid-state batteries due to its ultra-high theoretical specific capacity. However, the substantial volume change associated with the silicon–lithium alloying/dealloying process poses a significant challenge to the long-term cycling performance of silicon–carbon batteries, with the binder being a key component in mitigating this issue. Poly(acrylic acid) (PAA) is a prominent binder material due to the strong hydrogen bonding between its abundant carboxyl groups and the silanol (Si-OH) groups on the silicon surface. However, the linear chain configuration of conventional PAA hinders the formation of a three-dimensional (3D) cross-linked network, which is crucial for enhanced mechanical integrity. To address this challenge, this study proposes the incorporation of covalent organic frameworks (COFs)—which possess intrinsically developed cross-linked nanoporous channels and well-defined structure–property relationships—into the PAA system, developing a novel composite binder. Experimental results demonstrate that the electrode utilizing the COF-modified PAA binder retains a specific capacity of 727.9 mAh g⁻¹ after 250 cycles at 1.5 C, with a capacity retention rate of 77.32%. In contrast, the electrode using pure PAA as the binder delivers a capacity of only 505.5 mAh g⁻¹ under the same conditions. Further analysis of the SEI layer and theoretical calculations confirm that the introduction of COFs plays a crucial role in protecting the electrode sheet and promoting lithium-ion diffusion.