Unleashing the Power of Sn ₂ S ₃ Quantum Dots: Advancing Ultrafast and Ultrastable Sodium/Potassium‐Ion Batteries with N, S Co‐Doped Carbon Fiber Network

Abstract Tin sulfide (Sn ₂ S ₃ ) has been recognized as a potential anode material for sodium‐ion batteries (SIBs) and potassium‐ion batteries (PIBs) due to its high theoretical capacities. However, the sluggish ion diffusion kinetics, low conductivity, and severe volume changes during cycling have limited its practical application. In this study, Sn ₂ S ₃ quantum dots (QDs) (≈1.6 nm) homogeneously embedded in an N, S co‐doped carbon fiber network (Sn ₂ S ₃ ‐CFN) are successfully fabricated by sequential freeze‐drying, carbonization, and sulfidation strategies. As anode materials, the Sn ₂ S ₃ ‐CFN delivers high reversible capacities and excellent rate capability (300.0 mAh g ⁻¹ at 10 A g ⁻¹ and 250.0 mAh g ⁻¹ at 20 A g ⁻¹ for SIBs; 165.3 mAh g ⁻¹ at 5 A g ⁻¹ and 100.0 mAh g ⁻¹ at 10 A g ⁻¹ for PIBs) and superior long‐life cycling capability (279.6 mAh g ⁻¹ after 10 000 cycles at 5 A g ⁻¹ for SIBs; 166.3 mAh g ⁻¹ after 5 000 cycles at 2 A g ⁻¹ for PIBs). According to experimental analysis and theoretical calculations, the exceptional performance of the Sn ₂ S ₃ ‐CFN composite can be attributed to the synergistic effect of the conductive carbon fiber network and the Sn ₂ S ₃ quantum dots, which contribute to the structural stability, reversible electrochemical reactions, and superior electron transportation and ions diffusion.