Dual-Functional Polymer Binders for Silicon Based Electrodes

Abstract

As the “inert” materials in electrode, polymer binders play an important role in the long-term performance of silicon-based electrode. Several principles have been recognized to fabricate a “better” binder, there continues to be a lack of a rational design that would meet the robust criteria required for silicon (Si) anodes. Herein, we will present a synthetic polymer binder, i.e., catechol-functionalized chitosan cross-linked by glutaraldehyde (CS-CG+GA) that will serve both wetness-resistant adhesion capability via catechol grafting and mechanical robustness via in-situ formation of a three-dimensional (3D) network. The SiNPs 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). Properties which are traditionally considered to be advantageous, including stronger adhesion strength and higher mechanical robustness, do not always improve the binder performance. A semi-quantitative analysis on the main-chain scaling behavior and stiffness also demonstrated that both catechol grafting and crosslinking lead to the reduced flexibility of polymer backbone for the resultant binder system. It turns out that the end-to-end distance of the two adjacent crosslinking points (Re) should be no less than the persistence length (lp) of the chitosan backbone for an efficient binding performance. The relationship established between binder properties and electrochemical performance of consequent Si electrode is imperative for designing polymer binders with optimized electrochemical performance. The strategy of in-situ construction of a functional polymer network is instructive for the design of high-performance polymer binders not only for Si based anodes, but also for a wide variety of other types of alloy and conversion-based electrodes. Figure 1