Unveiling the Anomalous Expansion of Silicon-Carbon Composites Obtained by Chemical Vapor Infiltration Through Operando Charge Photometry and Dilatometry

Modern lithium-ion batteries increasingly incorporate pure silicon into the anode to boost energy density. However, practical deployment remains limited by silicon’s large cycling-induced volume changes, typically assessed by pouch cell dilatometry. While informative at the electrode-stack level, this method provides no direct insight into underlying particle-level behaviour. Here, we combine operando dilatometry with high-resolution charge photometry to correlate electrode-level expansion with single-particle swelling in state-of-the-art silicon anodes. We examined anode materials: (i) silicon-carbon (Si-C) composites prepared by silicon vapor deposition into porous carbon, and (ii) dense micron-sized silicon prepared by jet milling. Dilatometry revealed pronounced non-linear thickness evolution for Si–C composites, with reduced expansion at low state-of-charge, whereas micron-sized silicon exhibited linear expansion. Charge photometry reproduced these trends at the particle level, showing that the non-linear swelling of Si–C composites arises from internal porosity that delays external volume change during early lithiation. Dilatometry also captured significant first-cycle expansion irreversibility for both materials, while charge photometry showed largely reversible particle swelling, indicating that irreversibility originates from cell-level processes rather than intrinsic active material behaviour. Overall, these results establish charge photometry as a practical lab-based tool for resolving operando particle-scale chemo-mechanics and highlights the benefits of nano-engineered composite architectures for mitigating silicon expansion.