Highly porous SnO₂-SiO₂ composite microspheres with interconnected pores for long-cycle-life lithium-Iion batteries

The simultaneous suppression of volume changes through pore structure design and the control of surface side reactions using passivating materials is critical for achieving high electrochemical performance and structural stability in lithium-ion battery anodes. In this study, highly porous SnO₂-SiO₂ composite microspheres with interconnected pores (p-SnSi) were prepared using a simple, one-step spray pyrolysis process. Fine and spherical polystyrene beads, which were burned off during the process, created a highly open and porous structure that extended throughout the inner bulk and surface. The highly open and porous structure effectively mitigated the mechanical strain induced by volume changes during the charge and discharge cycles of SnO₂ while also providing a short lithium-ion diffusion length, thereby resulting in excellent electrochemical performance. Additionally, the SiO₂ layer in p-SnSi suppressed surface side reactions on highly porous SnO₂ with a large specific surface area, thereby enhancing the interfacial stability and contributing to improved cycling performance. The discharge capacities of the p-SnSi, filled structured SnO₂-SiO₂ composite microspheres (f-SnSi), porous SnO₂ microspheres (p-Sn), and filled structured SnO₂ microspheres (f-Sn) after 200 cycles at a current density of 1 A g^-1 were 523 ± 12, 96 ± 6, 101 ± 9, and 59 ± 1 mA h g^-1, respectively. Among these, p-SnSi demonstrated a higher lithium-ion storage capacity and capacity retention than f-SnSi, p-Sn, and f-Sn. In particular, the p-SnSi exhibited a stable reversible capacity of 544 ± 15 mA h g^-1 after 500 cycles at a current density of 1 A g^-1. These findings indicate that p-SnSi is a promising candidate for use in next-generation lithium-ion battery anodes.