Tailored silicon nanostructures in hydrogel-derived conductive binders: Role of size, structure, and surface chemistry in enhancing Li-ion battery performance

Silicon (Si) is a promising anode material for Li-ion batteries (LIBs), but its practical application is limited by volume expansion during lithiation/delithiation, leading to poor cycling stability. While Si nanostructuring mitigates this issue, it remains only a partial solution. This study systematically investigates the effects of Si particle size (6, 20, 55, or 100 nm), surface chemistry (type and degree of oxidation), and solid-state properties (amorphous vs. crystalline) on the electrochemical performance of Si-based anodes using a three-dimensional (3D) crosslinked polypyrrole (PPy) binder. In situ PPy polymerization around Si nanoparticles forms a 3D interconnected conductive network within the PPy/Si anodes, effectively accommodating volume changes and maintaining electrical contact during the galvanostatic cycling. The particle size dependence shows that larger Si nanoparticles provide higher initial charge capacity (2975 mAh/g), whereas smaller ones improve cycling stability (85 % capacity retention after 100 cycles). Amorphous Si exhibits significantly lower specific capacity but superior capacity retention (∼100 % after 100 cycles) compared to crystalline Si. Cyclic voltammetry and electrochemical impedance spectroscopy demonstrate that integrating 6 or 20 nm Si nanocrystals into a 3D crosslinked PPy enhances anode performance. These findings highlight the importance of optimizing Si properties in designing conductive hydrogel-derived anodes for high-performance LIBs. • Larger Si nanocrystals (100 nm) achieve higher initial capacity in LIB anodes. • Smaller Si nanocrystals (6 nm) improve cycling stability. • Amorphous Si nanoparticles outperform crystalline Si in cycling stability. • 3D crosslinked PPy accommodates Si volume expansion, enhancing anode performance. • Optimal Si size (6–20 nm) in PPy networks improves electrochemical performance.