Solid-state NMR study on sodium intercalation at low voltage window for Na₃V₂(PO₄)₃ as an anode

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Sodium-ion batteries (SIBs) are promising energy storage solutions.
• Understanding ion intercalation mechanisms is crucial for optimizing SIB performance.
• Na3V2(PO4)3 is a potential cathode material for SIBs.

Purpose of the Study:

• To investigate the sodium ion interaction behavior of Na3V2(PO4)3 at low voltage.
• To propose a new intercalation model for Na3V2(PO4)3.
• To elucidate the site-specific sodium ion insertion during electrochemical cycling.

Main Methods:

• In-situ X-ray Diffraction (XRD) to monitor structural changes.
• 31P Nuclear Magnetic Resonance (NMR) spectroscopy.
• 23Na Nuclear Magnetic Resonance (NMR) spectroscopy to track sodium ion dynamics.

Main Results:

• A novel intercalation model for Na3V2(PO4)3 was proposed.
• During the Na3V2(PO4)3 to Na4V2(PO4)3 transition, Na+ ions insert simultaneously into M1, M2, and M3 sites.
• During the Na4V2(PO4)3 to Na5V2(PO4)3 transition, Na+ ions predominantly insert into the M3 site.

Conclusions:

• The study provides detailed insights into the sodium ion intercalation mechanism in Na3V2(PO4)3.
• The proposed model clarifies the site occupancy of sodium ions at different electrochemical potentials.
• This understanding can guide the development of advanced cathode materials for sodium-ion batteries.