Silicon–Urea Network Nanocomposite Anodes with Enhanced Structural Connectivity via Thermal Rearrangement

Silicon is a promising anode material for lithium-ion batteries due to its high theoretical capacity, but its large volume change during cycling causes rapid capacity fading. In this study, a silicon–urea network (Si–UN) nanocomposite electrode was prepared using an organic sol-gel method to improve the structural stability of silicon electrodes. The urea network was synthesized by polymerizing multifunctional amine and isocyanate monomers in DMF, forming colloidal UN nanoparticles that can uniformly coat silicon particles during slurry preparation. Upon thermal rearrangement above 200 °C, the UN forms a thermally stable isocyanurate-based structure. The Si–UN electrode, fabricated by doctor blade casting without additional conductive carbon or a conventional polymer binder, delivered a capacity of over 2000 mAh g⁻¹. This result suggests that the rearranged UN structure enhances interparticle contact and supports charge-transfer pathways within the electrode. However, rapid capacity loss was observed after approximately 20–30 cycles, indicating that further optimization of the UN structure and the incorporation of a small amount of additional binder are required for long-term cycling stability. These results suggest that thermally rearranged UN can serve as a structural nanocomposite platform for silicon-based electrodes.