Overhauser Dynamic Nuclear Polarization of Lithiated Graphite Anodes: Probing Bulk and Surface Structures

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State NMR Spectroscopy

Background:

• Graphite is the ubiquitous anode material in high-energy density lithium-ion batteries.
• Anode performance is influenced by graphite's production methods, morphology, size, and defect levels.
• The solid electrolyte interphase (SEI) formation is critical for anode function but remains under investigation.

Purpose of the Study:

• To exploit the electronic conductivity of lithiated graphite anodes for enhanced nuclear magnetic resonance (NMR) signal detection.
• To investigate the Overhauser dynamic nuclear polarization (DNP) effect for improving NMR signals of bulk and surface nuclei.
• To explore factors affecting DNP enhancement and polarization transfer within lithium-ion battery anodes.

Main Methods:

• Utilized Overhauser dynamic nuclear polarization (DNP) coupled with NMR spectroscopy.
• Examined DNP enhancement factors (leakage, saturation, coupling) at various lithiation stages in artificial graphite.
• Studied the impact of particle size, morphology, electron relaxation, and conductivity in diverse graphite samples.

Main Results:

• Quantified DNP enhancement factors in artificial graphite across different lithiation levels.
• Demonstrated the influence of graphite properties (size, morphology, conductivity) on DNP efficiency.
• Showcased polarization transfer between bulk graphite and SEI species using ^6,7Li, ¹H, and ¹³C DNP NMR.

Conclusions:

• DNP is an effective technique for enhancing NMR signals in lithiated graphite anodes, aiding material characterization.
• Graphite properties significantly impact DNP enhancement, providing insights into anode material selection and performance.
• The study elucidates polarization dynamics between the anode and SEI, crucial for understanding battery degradation and improving longevity.