Achieving sustainable sulfur redox via d–p band overlap in Li0.80Cr0.67Ti0.33S2 cathodes for lithium-ion batteries

Anion redox reactions in layered cathode materials have attracted significant attention due to their remarkable potential to enhance the capacity and energy density of lithium-ion batteries. However, in conventional sulfide-based cathodes such as Li x TiS 2 , anionic redox is only partially reversible at high voltages and suffers from rapid capacity fading. These challenges primarily originate from the intrinsic electronic band structure of Li x TiS 2 , where the Ti 3+ /Ti 4+ redox couple lies far above the S 3 p band, suppressing ligand-to-metal charge transfer during Li + (de)intercalation. To overcome this limitation, we introduce a bandgap-engineering strategy via partial substitution of Ti 3+ with Cr 3+ , effectively narrowing the d- p bandgap and activating sustainable sulfur redox chemistry. The Cr-substituted compound, Li 0.80 Cr 0.67 Ti 0.33 S 2 , exhibits sustainable sulfur redox activity, thereby achieving a higher capacity of 223.0 mA h g −1 and nearly doubling the energy density of pristine Li 0.80 TiS 2 . Furthermore, Li 0.80 Cr 0.67 Ti 0.33 S 2 preserves its layered framework throughout the whole (de)lithiation process, indicating effective suppression of structural collapse during sulfur redox. Therefore, it demonstrates outstanding rate performance (77.5% capacity retention at 5.0C) and excellent long-term cycling stability (80% retention after 330 cycles), significantly outperforming its undoped counterpart. These findings highlight the critical role of ligand-metal d- p orbital overlap in enabling and stabilizing sustainable sulfur redox, providing valuable insights for the design of high-performance cathodes for next-generation lithium-ion batteries.