Quantitative Operando ⁷Li NMR Investigations of Silicon Anode Evolution during Fast Charging and Extended Cycling

Area of Science:

• Materials Science
• Electrochemistry
• Spectroscopy

Background:

• Fast charging protocols for lithium-ion batteries (LIBs) require understanding lithium speciation.
• Nuclear magnetic resonance (NMR) spectroscopy can identify and quantify lithium phases in battery anodes.

Purpose of the Study:

• To investigate the behavior of silicon (Si) electrodes during cycling and fast charging using NMR.
• To track lithium speciation and metal deposition in Si anodes.

Main Methods:

• Utilized a parallel-plate resonator radio frequency (RF) probe and a cartridge-type single-layer full cell.
• Employed 7Li magnetic resonance strategies to monitor Li-Si compounds and metallic Li formation.
• Performed electrochemical cycling at various rates (1C, 2C, 3C).

Main Results:

• Lithium silicide compounds exhibit nonlinear and asymmetric evolution during charging/discharging, unlike graphite.
• Metallic lithium deposition occurs as films and dendrites on Si anodes during fast charging.
• Li metal films show partial reversibility, while dendritic Li is entirely irreversible.

Conclusions:

• The intrinsic nonequilibrium behavior of Li-Si compounds impacts battery performance.
• Quantification of reversible and irreversible lithium deposition is critical for fast-charging protocol development.
• 7Li magnetic resonance is a powerful tool for evaluating these performance-governing properties in LIBs.