Development of Sn/SnO₂ hard carbon composites via solvothermal synthesis as anode material for sodium-ion and lithium-ion batteries

This research focuses on the development of carbon sphere composites derived from glucose and fructose, encapsulating metallic tin (Sn) via conventional and microwave-assisted solvothermal/hydrothermal synthesis for sodium-ion battery (SIB) anodes. The rationale behind combining Sn with hard carbon lies in Sn's high theoretical capacity through Na alloying, although its major drawback—up to 420% volume expansion—necessitates encapsulation strategies to maintain structural stability. A range of synthesis parameters, including temperature, precursor types, and solvents, were explored. Materials were subjected to pyrolysis at 600 °C, 850 °C, and 1100 °C. Notably, SnCl₂-derived composites showed superior Sn distribution and electrochemical stability compared to those from SnO₂. The best-performing sample, C2_SnCl2_600_1100, achieved a stable sodiation capacity of 418 mAh g⁻¹ over 100 cycles with 59.1% retention. Traditional solvothermal routes revealed issues like incomplete carbonization and Sn agglomeration, while microwave-assisted synthesis offered faster processing and improved stability. Raman, XRD, and SEM analyses confirmed phase evolution, graphitization, and morphology. Although Sn-containing composites showed poor cycling in lithium-ion batteries, they performed well in SIBs. Overall, this study presents a promising route to engineer Sn–carbon composites for sodium storage and highlights the potential of microwave-assisted synthesis to lower energy use while enhancing performance. Further optimization is necessary to advance these materials for next-generation energy storage.