The Critical Role of Binder pH in Determining the Stability of Si–Gr Composite Anodes

Abstract

Binder selection strongly influences silicon–graphite (Si–Gr) anode performance, yet the relationship between slurry processing, electrode structure, and electrochemical behaviour remains unclear. Here, we systematically investigate the influence of binder chemistry and binder pH on Si–Gr composite anodes using unmodified poly(acrylic acid) (PAA), lithiated PAA (LiPAA) at pH 5–7, and a conventional carboxymethyl cellulose (CMC) binder. Rheological, adhesion, zeta potential and microscopy analysis reveal that binder pH strongly governs slurry processability, binder–component interactions, and the resulting electrode structure. These differences were found to directly influence electrochemical performance in full cells versus NMC532. Among the binders studied, partially neutralised LiPAA at pH5 exhibited the most stable cycling performance, combining the favourable binder interactions associated with free acid PAA with the improved slurry processability required for practical electrode manufacturing. In contrast, unmodified PAA showed favourable electrochemical behaviour but poor rheological stability, while increasing binder pH resulted in progressively poorer electrode integrity, increased polarisation, and accelerated capacity fade. Differential capacity and electrochemical impedance analyses further revealed substantial differences in the electrochemical response and interfacial stability of the electrodes, while post‐mortem cross‐sectional scanning electron microscopy showed preservation of the electrode structure at pH 5 and severe structural degradation at pH 7 after 50 cycles. Overall, these results highlight the critical role of binder‐controlled processing in determining the stability of Si–Gr composite anodes by demonstrating how binder pH influences slurry interactions, electrode structure, and the subsequent electrochemical behaviour during cycling.