Tracking Electrochemical-Cycle-Induced Surface Structure Evolutions of Cathode Material LiMn₂O₄ with Improved...

Area of Science:

• Materials Science
• Electrochemistry
• Spectroscopy

Background:

• Capacity fading in lithium-ion batteries is linked to cathode material surface structure changes.
• Current methods often miss dynamic intermediate information during cycling.
• Raman spectroscopy offers a sensitive, non-destructive way to study surface structures.

Purpose of the Study:

• To investigate the dynamic surface structure evolution of LiMn2O4 during lithium-ion battery cycling.
• To correlate these surface changes with capacity fading.
• To demonstrate an improved operando Raman system for in situ characterization.

Main Methods:

• Developed and utilized an improved operando Raman spectroscopy system for real-time in situ measurements.
• Performed electrochemical testing, X-ray photoelectron spectroscopy (XPS), and conducted density functional theory (DFT) calculations.
• Analyzed Raman spectra to track surface phase evolution and bond changes during charging/discharging cycles.

Main Results:

• Revealed a direct correlation between electrode potential/Li content and surface structure changes in LiMn2O4.
• Observed biphase reactions, evolution of peroxo O-O bonds, and formation of Mn3O4 surface phase.
• Demonstrated a decrease in peroxo O-O bonds and a concurrent increase in Mn3O4 phase with increasing cycle number, linked to capacity fading.

Conclusions:

• The study establishes a direct link between dynamic surface structure evolution and capacity fading in LiMn2O4 cathodes.
• The improved operando Raman system provides valuable insights into in situ battery material characterization.
• Understanding these surface dynamics is crucial for developing more stable lithium-ion battery materials.