Composition and evolution of the solid-electrolyte interphase in Na2Ti3O7 electrodes for Na-ion batteries: XPS and...

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Sodium titanate (Na2Ti3O7) is a potential negative electrode material for sodium-ion batteries.
• Poor capacity retention in Na2Ti3O7 batteries is often linked to the instability of the solid-electrolyte interphase (SEI).

Purpose of the Study:

• To investigate the composition and evolution of the SEI on Na2Ti3O7 electrodes.
• To apply the Auger parameter analysis for accurate SEI characterization in battery materials.

Main Methods:

• X-ray photoelectron spectroscopy (XPS) was used to analyze the SEI.
• Auger parameter analysis was employed to overcome XPS limitations in energy assignment.
• Solid-state nuclear magnetic resonance (NMR) was used to study binder reactions.

Main Results:

• The SEI, composed of carbonates, fluorides, chlorides, and poly(ethylene oxide)s, was found to be unstable during cycling.
• Polyvinylidene difluoride (PVdF) binder reacts with sodium.
• Auger parameter analysis provided reliable SEI composition without calibration issues.

Conclusions:

• The instability of the SEI and binder reactions contribute to the poor performance of Na2Ti3O7 electrodes.
• The suitability of common lithium-ion battery binders and electrolytes for sodium-ion batteries is questionable.