ZnIn2S4 with a hybrid reaction mechanism and sulfur vacancies for sustainable sodium storage

Conventional monometallic sulfides are usually conversion or conversion-alloying-dominated anodes, while the sluggish kinetics and severe volume variation greatly hamper their electrochemical properties in sodium-ion batteries. Herein, bimetallic sulfides (V_s-ZnIn₂S₄) are developed with S vacancies, which are verified via electron paramagnetic resonance. A possible reaction mechanism (intercalation–conversion–alloying) is proposed, which is characterized by in situ X-ray diffraction. In addition, the small volume change during (de)sodiation of V_s-ZnIn₂S₄ is also observed by in situ transmission electron microscopy. The V_s-ZnIn₂S₄ anode shows ultrastable and superfast sodium storage performance, such as outstanding long-term cycling durability at 10 A g⁻¹ (349.6 mAh g⁻¹ after 2000 cycles) and rate property at 80 A g⁻¹ (222.7 mAh g⁻¹). Moreover, the full cell [V_s-ZnIn₂S₄//Na₃V₂(PO₄)₃/C] achieves an excellent property after 300 cycles (185.9 mAh g⁻¹) at 5 A g⁻¹, showing significant potential for real-world applications.