Quantitative lithium substitution of carboxyl hydrogens in polyacrylic acid binder enables robust SiO electrodes with durable lithium storage stability

The design of advanced binders plays a critical role in stabilizing the cycling performance of large-volume-effect silicon monoxide (SiO) anodes. For the classic polyacrylic acid (PAA) binder, the self-association of -COOH groups in PAA leads to the formation of intramolecular and intermolecular hydrogen bonds, greatly weakening the bonding force of the binder to SiO surface. However, strengthening the binder-material interaction from the perspective of binder molecular regulation poses a significant challenge. Herein, a modified PAA-Lix (0.25≤x≤1) binder with prominent mechanical properties and adhesion strength is specifically synthesized for SiO anodes by quantitatively substituting the carboxylic hydrogen with lithium. The appropriate lithium substitution (x=0.25) not only effectively increases the number of hydrogen bonds between the PAA binder and SiO surface owing to charge repulsion effect between ions, but also guarantees moderate entanglement between PAA-Lix molecular chains through the ion-dipole interaction. As such, the PAA-Li0.25/SiO electrode exhibits exceptional mechanical properties and the lowest volume change, as well as the optimum cycling (1237.3 mA h g−1 after 100 cycles at 0.1 C) and rate performance (1000.6 mA h g−1 at 1 C), significantly outperforming the electrode using pristine PAA binder. This work paves the way for quantitative regulation of binders at the molecular level.