Poly(acrylic acid) Grafted with a Boronic Ester and Dopamine as a Self-Healable and Highly Adhesive Aqueous Binder for Si Anodes

An aqueous cross-linked poly(acrylic acid) (PAA) polymer binder grafted with a boronic ester and dopamine, xPAA-B-DA, was developed herein for Si anodes. The reversible boronic ester bonds contribute to the self-healing characteristics of the binder, and dopamine improves its adhesive properties. A Si anode was fabricated by using xPAA-B-DA (Si@xPAA-B-DA), effectively inhibiting the volume expansion of Si while ensuring the structural integrity of the Si electrode. Unlike other studies employing self-healing boronic esters as a binder via boronic acid–diol cross-linking, this study adopts a novel approach by combining the cross-linking between boronic acid and the diol functionality in dopamine (involving self-healing properties) with intentionally retained dopamine to further increase the binder's adhesive performance. Accordingly, Si@xPAA-B-DA exhibits better adhesion and electrochemical performance than Si@xPAA-B (only containing cross-links between a boronic ester and a limited amount of dopamine) due to the synergy between the self-healing properties of boronic esters and the adhesive characteristics of dopamine. At a 0.5 C current density, the initial Coulombic efficiency is 74.9%; furthermore, even after 350 cycles, the capacity remains high at 1755.4 mAh g–1, yielding a 53.7% preservation of capacity. Moreover, after 200 cycles at a higher current density of 1 C, Si@xPAA-B-DA maintains 63.0% of its capacity, or 1674.3 mAh g–1. After 100 cycles, Si@xPAA-B-DA retains 70.8% of its capacity, which is notable even for a Si size of 350 nm.