Chitosan‑ g ‑Poly(acrylicacid) Copolymer and Its Sodium Salt as Stabilized Aqueous Bindersfor 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 (-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.