Deciphering Atomic Electronic Structure Dynamics and Site Occupancy Transitions in Dictating Sodium Storage in Hard...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Hard carbon (HC) is crucial for sodium-ion batteries.
• HC sodiation mechanisms are complex due to structural heterogeneity.
• Understanding sodiation is vital for rational HC design.

Purpose of the Study:

• To elucidate the sodiation mechanism in hard carbons.
• To investigate the role of the carbon matrix in sodiation.
• To develop an advanced theoretical framework for HC sodiation.

Main Methods:

• Utilized high-resolution 13C Nuclear Magnetic Resonance (NMR).
• Employed operando 23Na NMR spectroscopy.
• Analyzed sodium ion occupancy and diffusion dynamics.

Main Results:

• Identified carbon layers lining micropore walls contributing to electronic structure.
• Observed a transition in sodium ion occupancy from interlayers to micropores.
• Demonstrated that the carbon matrix, not just pore architecture, controls plateau electrochemistry.
• Found a reduction in Na+ diffusion coefficient due to synergistic changes.

Conclusions:

• Established a three-stage theoretical framework for HC sodiation.
• Highlighted the importance of tailoring electronic environments and Na+ occupancy.
• Provided conclusive evidence for the carbon matrix's role in HC sodiation.