Cooperation of Covalent Bonds and Coordinative Bonds Stabilizing the Si-Binder-Cu Interfaces for Extending Lifespan of Silicon Anodes

Abstract

Binders provide a straightforward and efficient strategy to mitigate the significant challenge of volume expansion in silicon anodes for lithium-ion batteries. To improve the cycle life of silicon anodes, a cross-linked binder (CMC-DP) is designed and synthesized using carboxymethyl cellulose, phytic acid, and pyrrole. The numerous hydroxyl groups in phytic acid provide abundant binding sites for the formation of hydrogen and ester bonds. The formation of hydrogen bonds and covalent bonds enhances the mechanical properties of the adhesive. The amino groups in the binder form N─Si─O covalent bonds with silicon particles, while the hydroxyl and carboxyl groups form ─(COO)2Cu and ─(OH)2Cu coordination bonds with the copper foil, enhancing interfacial adhesion. When the CMC-DP10 binder is applied to silicon nanoparticles (~30 nm), the specific capacity of the electrode can be maintained at around 1700 mAh g-1 after 500, whereas the CMC binder achieves only ~100 mAh g-1 under the same conditions. The results of the study showed that the CMC-DP binder has strong adhesion to both silicon nanoparticles and copper foils.

Keywords: cross-linked binders, Si anode, covalent bonds, coordination bonds, interfaces interaction