Effect of Sodium Polyacrylate-Carboxymethyl Cellulose Binder Composition on the Electrochemical Stability of Silicon Monoxide Anodes

Silicon monoxide (SiO) has attracted considerable attention as an anode material for lithium-ion batteries owing to its relatively high theoretical capacity and mitigated volume expansion compared with elemental silicon. Nevertheless, its long-term electrochemical performance is still constrained by the simultaneous occurrence of mechanical degradation and electrochemical instability during repeated cycling. Although various binder combinations have been explored to address these challenges, whether all binder combinations can consistently deliver improved performance remains insufficiently understood. In this study, we systematically investigate the effect of binder composition on the mechanical characteristics and electrochemical behaviour of unmodified SiO anodes using sodium polyacrylate (NaPAA) and carboxymethyl cellulose (CMC) as a model dual-binder system. Mechanical assessments and SEM observations reveal that NaPAA primarily contributes strong interfacial adhesion, whereas CMC reinforces the mechanical framework required to accommodate volume changes during cycling. Electrochemical measurements demonstrate that a NaPAA–CMC (6:4) composition achieves an initial coulombic efficiency of 60.6% and maintains a reversible capacity of 1288 mAh/g after 100 cycles at a current density of 0.1 C. Rather than introducing a new binder chemistry, this work highlights that electrochemical stability in SiO anodes is governed by achieving an appropriate balance between adhesive and mechanical functions within the binder system. These findings provide a degradation-aware perspective for rational binder selection in silicon-based lithium-ion batteries.