Chitosan-g-Poly(acrylic acid) Copolymer and Its Sodium Salt as Stabilized Aqueous Binders for Silicon Anodes in Lithium-Ion Batteries

Silicon (Si) anodes display high specific capacity but mostly suffer from poor cycling ability owing to their dramatic volume expansion during the discharge/charge process. An effort was devoted to developing new polymeric binders that could effectively mitigate the capacity fading of Si anodes. Herein, aqueous binders of chitosan-g-poly(acrylic acid) copolymer (CS–PAA) and its sodium salt (CS–PAANa) have been synthesized and applied as the functional binders for the stabilization of Si anodes in lithium-ion batteries. The structure and properties of Si anodes based on CS–PAA and CS–PAANa were comparatively characterized by using poly(vinylidene fluoride), chitosan, and poly(acrylic acid) as reference binders. Unlike conventional 1D structural binders, the CS–PAA and CS–PAANa form a cross-linked (3D) network during curing, which maintains mechanical integrity to mitigate Si nanoparticle pulverization effectively. Moreover, the abundant polar groups including carboxylic acid (−COOH) and carboxylate (−COO–) in the two binders could react with both Si nanoparticles and copper (Cu) current collector to offer robust adhesion, significantly improving electrode integrity after the repeated delithiation/lithiation cycles. Benefitting from the structural advantages, the Si/CS–PAA and Si/CS–PAANa electrodes deliver stable cycling performances of 1243 and 1608 mA h/g at 420 mA/g after 100 cycles.