Mechanical Response and Crack Propagation in Si/C Composite Electrodes During Electrochemical Cycling: the Critical Influence of Polymeric Binders

Silicon-carbon (Si/C) composite anodes are considered ideal replacements for traditional graphite anodes due to their high specific capacity. However, their significant volume changes during charge-discharge cycles readily lead to rapid capacity decay and mechanical failure of the electrodes, severely limiting their practical application. As a key component in electrodes, the binder is essential for preserving the mechanical integrity of the composite electrode and for constraining the expansion of active materials. This study ,an in-situ curvature measurement system was utilized to evaluate the impact of binders, i.e. polyacrylic acid (PAA), carboxymethyl cellulose (CMC), and polyvinylidene fluoride (PVDF), on the bending deformation, modulus, partial molar volume and stress-strain behavior of Si/C composite electrodes during lithiation/delithiation cycles. Then, scanning electron microscopy was used for systematic characterization the changes of electrode surface and cross-sectional morphologies. The results indicated that the Si/C composite electrodes with PAA could maintain relatively best electrochemical performance and structural integrity, owing to its large Young's modulus and strong confinement capability and which can effectively suppress its volume changes. While, the electrode with PVDF binder showed significant cracking evolution and interfacial delamination due to its lower modulus and poor bonding strength. This study reveals the working mechanism of the binder’s influence on the electrode stability from a mechanical-electrochemical coupling perspective, which can provide crucial theoretical and experimental basis for the rational design and optimization of superior Si/C anode binders.