Exploiting S22−/S2− redox chemistry in pseudo-layered chain-structured titanium trisulfide cathodes for high-energy magnesium–lithium hybrid ion batteries†

Magnesium–lithium hybrid ion batteries (MLIBs) offer a compelling alternative to conventional lithium-ion batteries (LIBs) due to their enhanced safety, abundant magnesium resources, and high theoretical capacities. However, the lack of high-capacity cathode materials has hindered their widespread application. In this study, we explore the potential of pseudo-layered titanium trisulfide (TiS₃) as a novel cathode material for MLIBs. TiS₃ features a chain-like structure with both S₂²⁻ and S²⁻ species, providing abundant ion storage sites and leveraging an S₂²⁻/S²⁻ redox mechanism. The TiS₃ electrode achieves a maximum reversible capacity of ca. 381 mA h g⁻¹, corresponding to a high energy density of ca. 483 W h kg⁻¹, along with robust rate capability (ca. 213 and 138 mA h g⁻¹ at 1000 mA g⁻¹, 2.69C, and 3000 mA h g⁻¹, 8.06C, respectively) and extended cycling stability (ca. 160 mA h g⁻¹ after 1700 cycles at 2.69C). Mechanistic insights obtained via ex situ X-ray absorption spectroscopy (XAS) confirm the S₂²⁻/S²⁻ redox mechanism, while in operando powder X-ray diffraction (PXRD) reveals phase transitions linked to intercalation-induced changes in local structure. This work underscores the promise of anionic redox chemistry in inorganic intercalation compounds and offers a new pathway for designing high-performance cathode materials for next-generation MLIBs and beyond.