A Key to Material's Stability: Tuning Pyrolysis Temperature in SnS_x@C Anodes for Sodium-Ion Batteries

Developing robust and efficient anodes is essential for advancing sodium-ion battery technology. Herein, a systematic investigation of SnS_x@C composites prepared at different pyrolysis temperatures to elucidate how their structural, surface, and electrochemical properties govern sodium-ion storage is reported. The study reveals that a lower synthesis temperature traps extra sulfur within the carbon matrix, which hampers the complete SnS conversion reaction and Na⁺ intercalation processes. In contrast, pyrolysis at 800 °C facilitates more thorough sulfur release, yielding a defect-rich but stable carbon matrix that supports enhanced sodiation/desodiation reversibility. Operando Raman spectroscopy and X-ray photoelectron spectroscopy depth profiling confirm that the pyrolysis temperature strongly affects the formation and stability of the solid electrolyte interphase. The SnS_x@C material pyrolyzed at 800 °C not only possesses superior ion transport characteristics but also delivers enhanced electrochemical performance, maintaining a stable capacity of ≈500 mAh g^-1 at C/10 and retaining a substantial fraction of its capacity over 100 cycles, in contrast to the rapidly decaying capacity of the material pyrolyzed at 600 °C.