A Key to Material's Stability: Tuning Pyrolysis Temperature in SnS _x @C Anodes for Sodium‐Ion Batteries

Abstract 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.