A Tough and Self-Healable Semi-IPN Hydrogel Binder Based on Multiple Dynamic Bonds for Si Anodes in Lithium-Ion Batteries

In recent years, hydrogels have garnered significant attention as potential binders for silicon (Si) anodes in lithium-ion batteries (LIBs), owing to their elasticity, flexibility, and adhesion properties that accommodate the substantial volume changes characteristic of Si during charge-discharge cycles. In addition, their environmental benefits are further amplified by using water as a solvent. Despite their promising attributes, conventional hydrogels frequently exhibit insufficient mechanical robustness, making them susceptible to structural degradation under the demanding conditions of battery operation. Herein, we developed a semi-interpenetrating polymer network (semi-IPN) hydrogel. By incorporating multiple dynamic bonds into the network, we achieved balanced properties between the self-healing ability and mechanical strength. This hydrogel was fabricated by combining the network of acrylic acid (AAc) cross-linked with B-N coordinated boronic ester bonds bearing a cross-linker (N-BE cross-linker) and the network of carboxymethyl cellulose (CMC). Further, metal coordination bonds between Al³⁺ and the skeleton of the hydrogel give robust mechanical strength and adhesion properties. The prepared hydrogel binder effectively mitigates Si's bulk expansion and promotes a more stable solid electrolyte interphase (SEI) during extended cycling, owing to the 3D structure of the hydrogel network and abundance of functional groups capable of forming hydrogen bonds with the Si anode surface. Si anodes utilizing this composite binder exhibit a reversible specific capacity of 1023.8 mAh g^-1 after 300 cycles at 0.2 C, significantly outperforming conventional PVDF-binder anodes which remain only 308.3 mAh g^-1 under identical conditions. This improvement in capacity retention demonstrates the superior performance of the semi-IPN hydrogel binder for Si anodes in LIBs.