Structural characterization of an amorphous VS₄ and its lithiation/delithiation behavior studied by solid-state NMR...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Vanadium sulfide (VS₄) is a promising cathode material for next-generation lithium-ion batteries due to its high theoretical capacity.
• Crystalline VS₄ possesses a unique structure with one-dimensional V-V bonded chains linked by van der Waals forces.

Purpose of the Study:

• To investigate the lithiation/delithiation behavior of amorphous VS₄.
• To understand the structural and chemical transformations during battery cycling.

Main Methods:

• Amorphous VS₄ was prepared using mechanical milling.
• Solid-state nuclear magnetic resonance (NMR) spectroscopy was employed to study lithiation/delithiation.

Main Results:

• Amorphous VS₄ exhibits a chain structure similar to its crystalline counterpart.
• Lithiation causes significant structural changes, forming Li₃VS₄ with tetrahedral coordination and altered V/S valence states (V⁴⁺ to V⁵⁺, S^- to S^2-).
• A reversible capacity of 700 mA h g^-1 was achieved between 1.5 and 2.6 V, with the material recovering a disordered chain structure after the first cycle without forming elemental V.

Conclusions:

• Amorphous VS₄ is a viable cathode material for lithium-ion batteries, offering high reversible capacity.
• The material undergoes reversible structural and chemical changes during cycling, avoiding detrimental conversion reactions.
• The disordered yet recoverable chain structure of amorphous VS₄ is key to its electrochemical performance.