Electrochemical Interlayer Expansion and Dual Redox Activation for Fast Mg-Ion Transport and High Capacity in Quasi-1D TiS3

Magnesium ion batteries (MIBs) offer promising solutions for next-generation sustainable energy storage systems owing to their intrinsic safety and cost-effectiveness, yet their development is hindered by the scarcity of high-capacity cathode materials, primarily due to poor magnesium ion transport and a limited number of electrochemically active sites. Here, we report a significant performance breakthrough in a structurally and electrochemically distinct, underexplored quasi-1D pseudolayered titanium trisulfide (TiS3) cathode through interlayer engineering and exploitation of dual cationic/anionic redox chemistry. In operando and ex situ characterization reveal that interlayer expansion, induced by the intercalation of 1-butyl-1-methylpyrrolidinium (BMPyrr+), weakens electrostatic interactions within the sulfide sublattice, enhances magnesium ion diffusion kinetics, and increases accessible redox sites. These modifications activate reversible Ti4+/Ti3+ and S22–/S2– redox couples, complemented by nanosizing-induced pseudocapacitance, synergistically underpinning the exceptional electrochemical performance. As a result, the expanded TiS3 cathode delivers outstanding reversible capacities (up to 300 mA h g–1 at 100 mA g–1), excellent rate performance (181 mA h g–1 at 1000 mA g–1), and long-term cycling stability, surpassing its pristine counterpart and many state-of-the-art MIB cathodes. This work underscores the combined role of interlayer engineering and dual-ion redox chemistry in advancing multivalent energy storage and introduces pseudolayered TiS3 as a new structural platform beyond conventional layered sulfides.