Influence of aqueously synthesized polyacrylic acid binder content on the processing and cycling of Si–Gr anodes

Polyacrylic acid (PAA) is an emerging binder for silicon–graphite (Si–Gr) composite anodes due to its strong affinity for the native SiO x layer that covers Si particles and its ability to act as an artificial solid–electrolyte interphase (SEI). Here, PAA with a high molecular weight (M w = 845 kg mol −1 ) is synthesized using a green, aqueous route. The effect of varying PAA content (from ⁓3 to 15 wt%) on electrode processing, physical properties, and cycling stability is systematically investigated. Increasing PAA concentration improves slurry stability and dispersion, widening the electrode processability window. X-ray photoelectron spectroscopy (XPS) confirms that PAA preferentially localizes on the silicon surface, with evidence of agglomeration at higher concentrations. An optimal PAA content of 10.6 wt% delivers the highest reversible specific capacity and good cycling stability (1270 mAh g electrode −1 at the 50th cycle in half cell and 860 mAh g electrode −1 in full cell). Lower PAA content results in deficient binder networks and increased irreversible capacity, while excessive binder content leads to binder agglomeration and increased resistivity. Post-mortem solid-state NMR analysis further supports the role of PAA as an artificial SEI, mitigating uncontrolled electrolyte decomposition and lithium loss. • Aqueous PAA synthesis method yields effective binder material for Si-Gr anodes. • Increasing binder content improves slurry rheology and processability. • PAA is preferentially adsorbed on the silicon surface. • Binder coverage ratio is optimized for electrochemical performance. • Post-mortem NMR analysis confirms PAA binder serves as an artificial SEI.