Unveiling the Role of Sodium Ions in Modulating the Molecular Structure of Polyacrylic Acid for Stable Operation of Silicon‐Based Anodes

ABSTRACT Polyacrylic acid (PAA) is a promising binder for addressing the unstable issues induced by enormous volume expansion of silicon‐based anodes, yet it struggles to deliver long‐term cycling stability due to its poor toughness. Herein, we incorporated sodium ions (Na + ) into PAA to form PAA‐Na binder with charged sodium carboxylate groups. The resulting electrostatic repulsion stretches the coiled polymer chains of PAA, thereby enhancing its toughness, which enables the effective encapsulation and entanglement of micro‐sized silicon particles (µSi), thereby mitigating its volume expansion and maintaining the electrode structural stability. As expected, the as‐constructed µSi electrode (µSi@SWCNT@PAA‐Na) delivers a high specific capacity of 1119.8 mAh g −1 at 0.8 A g −1 over 400 cycles, superior to most previously‐reported advanced binder‐based µSi electrodes. Furthermore, the binder also enables stable operation of SiO x anodes, achieving a high capacity retention of 96.8% after 230 cycles at 0.3 A g −1 . The as‐fabricated NCM811/SiO x @PAA‐Na full cell maintains outstanding cycling performance, retaining 99% capacity retention after 300 cycles at 27 mA g −1 . More importantly, Finite element simulations visually reveal the superior stress distribution capability of PAA‐Na binder. This work enables stable operation of high‐capacity silicon anodes for energy‐dense batteries through rational molecular design of conventional binder systems.