Microstructure-Tuned Tin-Embedded N-Doped Hollow Carbon Spheres for Advanced Lithium-Ion Batteries

To enhance the Li storage capacity in carbon materials, incorporation of Sn into the carbon matrix fabricates Sn@C composites for lithium-ion batteries (LIBs). Due to the trade-off between the Sn content and particle size, high capacity and long-term stability cannot simultaneously be achieved in LIBs. Meanwhile, which factor holds importance and at what stage to influence the performance have remained unanswered due to the challenges of achieving a well-controlled morphology and Sn distribution. Herein, a multistep strategy using functional polymer-mediated Sn loading, layer encapsulation, and carbonization was utilized to embed Sn into N-doped hollow carbon spheres for affording Sn-content- and particle-size-tunable Sn@h-NCs. Adjusting the SnCl2 addition can fine-tune the Sn content up to 27.1 wt %, while Sn aggregation causes structure transformation from hollow to yolk–shell configurations. When employed as anodes for LIBs, Sn@h-NCs exhibit a high initial discharge capacity of 1314 mAh g–1 at 30 mA g–1, along with a superior cycling-stability, maintaining 705 mAh g–1 at 0.5 A g–1 after 150 cycles, much higher than the performance of NCs. However, aggregation-induced increase in Sn particle size results in elevated overpotential and resistance, suggesting that higher Sn-content Sn@h-NCs deliver superior capacity at a lower current density, while Sn@h-NCs with a lower content offer comparable capacity but improved stability at a higher current density.