In situ crosslinkable acrylic random copolymer binders for silicon anodes in lithium‐ion batteries

Abstract

Silicon is in the spotlight as a promising anode material for next-generation Li-ion batteries. However, its practical application is limited by a rapid decay in capacity due to considerable volume changes. Rational design of binders that can exhibit strong adhesion and robust mechanical properties is crucial for overcoming such challenges. Herein, we synthesize a series of multifunctional acrylic random copolymers comprising various ratios of acrylic acid and glyceryl groups by free-radical polymerization. The adhesive and mechanical properties of the binders are systematically modulated, and their impact on the electrochemical properties of a Si-nanoparticle anode are investigated. Owing to the presence of both acrylic acid and hydroxyl groups, the copolymers containing 7 mol% and 25 mol% glyceryl group undergo in situ crosslinking under mild thermal treatment (70°C for 24 h). In particular, the copolymer containing 7 mol% glyceryl group exhibits the highest specific capacity and capacity retention (1170 mAh g−1 and 54% after 100 cycles at 0.5 A g−1, respectively), which is superior to those of a conventional poly(acrylic acid) binder (880 mAh g−1 and 52% after 100 cycles at 0.5 A g−1). The enhanced electrochemical properties attribute to the improved adhesive and mechanical properties enabled by the network structure.