Amorphous TiO₂ Shells: A Vital Elastic Buffering Layer on Silicon Nanoparticles for High-Performance and Safe Lithium Storage

Smart surface coatings of silicon (Si) nanoparticles are shown to be good examples for dramatically improving the cyclability of lithium-ion batteries. Most coating materials, however, face significant challenges, including a low initial Coulombic efficiency, tedious processing, and safety assessment. In this study, a facile sol-gel strategy is demonstrated to synthesize commercial Si nanoparticles encapsulated by amorphous titanium oxide (TiO₂), with core-shell structures, which show greatly superior electrochemical performance and high-safety lithium storage. The amorphous TiO₂ shell (≈3 nm) shows elastic behavior during lithium discharging and charging processes, maintaining high structural integrity. Interestingly, it is found that the amorphous TiO₂ shells offer superior buffering properties compared to crystalline TiO₂ layers for unprecedented cycling stability. Moreover, accelerating rate calorimetry testing reveals that the TiO₂-encapsulated Si nanoparticles are safer than conventional carbon-coated Si-based anodes.