Microstructure-Dependent Sodium Storage Mechanisms in Hard Carbon Anodes.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sustainable energy storage is critical for renewable energy integration.
• Sodium-ion batteries (NIBs) offer a sustainable and cost-effective alternative for grid-scale storage.
• Hard carbon (HC) is a promising anode material for NIBs, but its complex structure hinders understanding of sodium storage.

Purpose of the Study:

• To elucidate the influence of hard carbon microstructure on sodium storage mechanisms in NIBs.
• To differentiate sodium storage behavior in the high-potential (slope) and low-potential (plateau) regions of the NIBs.
• To provide insights into microstructure engineering for enhanced HC anode performance.

Main Methods:

• X-ray total scattering experiments to probe atomic structure.
• Density functional theory (DFT) calculations to model sodium interactions.
• Analysis of sodium storage mechanisms across different potential regions.

Main Results:

• In the slope region, sodium initially binds to defect sites before intercalating between graphene layers.
• Initial irreversibility is linked to sodium trapping at surface defects and solid electrolyte interface (SEI) formation.
• In the plateau region, sodium intercalates and fills pores, with cluster size depending on pore size and defect concentration.

Conclusions:

• Hard carbon microstructure significantly dictates sodium storage mechanisms and performance in NIBs.
• Understanding defect sites, pore structure, and interlayer spacing is crucial for optimizing HC anodes.
• Microstructure engineering of hard carbons is vital for advancing NIB technology for grid-scale applications.