# Electrochemical Interlayer Expansion and Dual Redox Activation for Fast Mg-Ion Transport and High Capacity in Quasi-1D TiS 3

## TL;DR

This paper introduces a new cathode material, TiS3, that improves magnesium-ion battery performance through interlayer expansion and dual redox chemistry.

## Contribution

The study introduces interlayer engineering and dual redox activation in TiS3 for enhanced Mg-ion transport and capacity.

## Key findings

- Expanded TiS3 cathode achieves up to 300 mA h g–1 at 100 mA g–1.
- The material shows excellent rate performance of 181 mA h g–1 at 1000 mA g–1.
- Long-term cycling stability is achieved, outperforming many existing MIB cathodes.

## Abstract

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 S2
2–/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.