Low-Cost Tin Compounds as Seeds for the Growth of Silicon Nanowire–Graphite Composites Used in High-Performance Lithium-Ion Battery Anodes

Abstract

Nanostructured silicon–graphite composites range among the best options for achieving next-generation high-energy anodes for high-performance lithium-ion batteries. Growing silicon nanowires on graphite give access to composites with high capacity and stability, as the silicon distributes homogeneously in the electrode, and the direct contact provides enhanced mechanical stability even in silicon-rich (>25 wt %) active materials. However, the cost-effective production of such composites remains a challenge. Here, we introduce low-cost catalysts, tin sulfide and tin oxide, enabling silicon nanowire growth at a lower temperature than with widely used gold catalysts, and investigate their impact on the composite nanostructure and composition. The small difference detected in the composition of the products obtained with both catalysts required the development of a reliable method to measure the low-level oxygen content and distribution within the composite. It revealed that oxygen from the SnO2 growth seeds is incorporated into the silicon nanowires, while no sulfur from the SnS catalyst could be detected. We show that SnS seeds result in an anode material of superior initial Coulombic efficiency of 81%, while capacity, stability in cycling, and rate capability are less affected by the choice of the catalyst. The composite anodes, optimized for a capacity of 1000 mAh g–1 at C/5 rate, deliver an areal capacity of up to 3.6 mAh cm–2 and 82% capacity retention over 200 cycles. Their rate capability of 780 mAh g–1 at 5C surpasses that of gold-seeded silicon–graphite composites. The insight obtained from this study provides guidance for the reliable low-cost synthesis and quality control of silicon-containing active materials for Li-ion battery anodes.