Design of Multifunctional Binder for High-Capacity Silicon Based Anodes

Abstract

The role of binder material for silicon (Si) and other metal alloy based anodes is critical for their long-term performance. Although several principles have been recognized to fabricate a “better” binder, there seems to be a lack of a rational design and synthesis approach that would meet the robust criteria required for metal alloy anodes. This presentation will discuss the synthesis and characterization of a novel polymer binder, a catechol-functionalized chitosan cross-linked by glutaraldehyde (CS-CG+GA), that serves dual functionalities: a) provides wetness-resistant adhesion capability via catechol grafting and b) possesses mechanical robustness via in-situ formation of a three-dimensional (3D) network. A Si nanoparticle (SiNP) based anode with the designed functional polymer network (CS-CG10%+6%GA) exhibits a capacity retention of 91.5% after 100 cycles (2144 ± 14 mAh/g). This study shows that traditional “better” properties including stronger adhesion strength and higher mechanical robustness do not always improve binder performance, but rather Si anode performance is governed by a delicate synergy of various polymer properties. The clear relationship between grafting density of adhesion groups and degree of crosslinking for ultimate electrochemical performance of polymer binders is established by assessing the rheological behavior of polymer solution, mechanical property of anode coating, adhesion force with SiNPs, peel stress of anode coating, morphology evolution of electrode, and the semi-quantitative evaluation on the scaling behavior and stiffness of the polymer backbone. This study provides a clear path for the rational design of high-performance functional polymer binders for not only Si-based electrodes, but also for other types of alloy and conversion-based electrodes.