Boosting anionic redox of TiS4 via Se anion doping for high-performance Al-ion batteries

Aluminum-ion batteries (AIBs) are gaining attention for large-scale energy storage due to their low cost and high theoretical capacity. However, the existing cathode materials frequently encounter rapid capacity degradation and sluggish reaction kinetics due to the strong interaction with high-charge Al³⁺, which limits the utilization of AIBs. Here, the Se-doping strategy is proposed to facilitate the active participation of anions in charge compensation and enhance the anionic redox process of amorphous anion-rich TiS₄. A refined amount of Se doping effectively improves reaction kinetics for Al-storage and stabilizes the structure of the material, preventing polysulfide dissolution under high dealumination states. As a result, amorphous TiS_3.5Se_0.5 delivers unprecedented Al³⁺ storage performance, with a stable capacity of 210 mAh g⁻¹ at 500 mA g⁻¹ over 400 cycles. Through detailed characterization, we reveal that a-TiS_3.5Se_0.5 undergoes reversible Al³⁺ insertion, accompanied by anionic redox processes involving S₂^2- and Se^n- species, which lays the foundation for further development of anionic-redox-based cathodes for high-performance AIBs.