# Self-Supporting Quasi-1D TaS3 Nanofiber Films with Dual Cationic/Anionic Redox for High-Performance Mg–Li Hybrid Ion Batteries

## TL;DR

A new self-standing TaS3 nanofiber film improves magnesium-lithium hybrid battery performance through dual redox reactions and structural stability.

## Contribution

A carbon- and binder-free TaS3 nanofiber film is developed for Mg–Li hybrid batteries with dual cationic/anionic redox and structural integrity.

## Key findings

- TaS3 nanofiber electrode achieves 178.5 mA h g–1 reversible capacity at 50 mA g–1.
- Maintains 91.6% capacity after 100 cycles and performs well at high current densities.
- Structural integrity is preserved during cycling, enabling stable and flexible energy storage.

## Abstract

Magnesium–lithium
hybrid ion batteries (MLIBs) offer a promising
energy storage technology that combines the safety and dendrite-free
plating/stripping of Mg anodes with the rapid Li+-dominated
diffusion in cathode materials. However, for electrodes that undergo
significant volume/structural changes during cycling, conventional
slurry-cast fabrication often leads to microstructural degradation,
active material detachment, and consequently, poor cycling stability
and rapid capacity fading. Here, we report a self-standing, carbon-
and binder-free tantalum trisulfide (TaS3) nano fibrous
(NF) film, synthesized via a facile one-step physical vapor transport
reaction that addresses these challenges through mechanistic innovations.
Mechanistic investigations reveal that the TaS3 NF electrode
undergoes dual cationic (Ta5+/Ta3+) and anionic
(S2
2–/S2–) redox reactions,
accompanied by electrochemically induced phase transitions and in situ exfoliation. The dual redox couples provide a large
number of Li+ ion storage sites, while the structural changes
lead to fiber-level nanosizing, which in turn promotes fast (near)
surface ion storage and pseudo capacitive behavior. Despite these
significant transformations, the robust fibrous architecture retains
structural integrity throughout prolonged cycling, as confirmed by in
operando and ex situ characterization. This dual-redox, in situ exfoliation,
and architecture-driven mechanism underpins the electrode’s
exceptional cycling stability and high rate capability. As a result,
the TaS3 NF electrode achieves a high reversible capacity
of 178.5 mA h g–1 at 50 mA g–1, maintains 91.6% of reversible capacity after 100 cycles, and delivers
144.4 and 119.0 mA h g–1 at 500 and 1000 mA g–1, respectively, surpassing those of slurry-cast bulk
TaS3 controls. Furthermore, the maintenance of a flexible
film structure after extended cycling suggests potential applicability
in next-generation wearable and structurally adaptive energy storage
systems. These findings highlight the potential of self-standing,
carbon- and binder-free film electrodes in advancing the cycling stability,
energy density, and design versatility of MLIB systems and beyond.