Supramolecularly Reinforced Silicon Anodes via UPy Functionalization

Silicon (Si) is considered one of the most promising anode materials for next-generation lithium-ion batteries owing to its exceptionally high theoretical capacity. However, the significant volume changes during repeated lithiation and delithiation lead to particle pulverization, electrode cracking, and unstable solid electrolyte interphase (SEI) formation, resulting in rapid capacity fading and poor cycling stability. To overcome these challenges, ureidopyrimidinone (UPy)-functionalized silicon (Si-UPy) was developed to introduce dynamic multiple hydrogen-bonding interactions that enhance interparticle adhesion and mechanical elasticity. The reversible nature of the UPy dimer enables efficient stress dissipation while maintaining strong cohesion between silicon particles during repeated volume changes.

Si-UPy was synthesized through surface functionalization of silicon particles, and successful modification was confirmed by FT-IR, XPS, and TEM analyses. Mechanical and electrochemical properties were systematically evaluated through adhesion tests, nanoindentation, galvanostatic cycling, electrochemical impedance spectroscopy, and rate capability measurements. Among the investigated compositions, the SiUPy20 electrode (Si:Si-UPy = 80:20 wt%) exhibited the best balance between mechanical robustness and electrochemical performance, demonstrating improved cycling stability, reduced charge-transfer resistance, enhanced lithium-ion diffusivity, and superior rate capability compared with the pristine Si electrode. Post-mortem SEM and XPS analyses further revealed that the hydrogen-bonding network effectively maintained the structural integrity of the electrode after prolonged cycling. These findings demonstrate that UPy-based supramolecular engineering provides an effective molecular design strategy for mechanically adaptive and durable silicon anodes, offering a promising approach toward high-performance lithium-ion batteries.