Tuning Bulk Redox and Altering Interfacial Reactivity in Highly Fluorinated Cation-Disordered Rocksalt Cathodes

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Lithium-excess, cation-disordered rocksalt (DRX) materials are promising Li-ion battery cathodes.
• Parasitic degradation reactions at the cathode-electrolyte interface limit their performance.

Purpose of the Study:

• To investigate interfacial degradation mechanisms in Mn-based DRX oxyfluorides.
• To quantify bulk redox and surface degradation reactions during high-voltage cycling.

Main Methods:

• Differential electrochemical mass spectrometry (DEMS) and titration mass spectrometry.
• Electrochemical cycling with a high-voltage cutoff (4.8 V vs Li/Li+).
• Ex situ spectroscopy (XPS, ICP-OES, ssNMR) and fluoride-scavenging additive experiments.

Main Results:

• Increasing fluorine content suppressed oxygen redox and O2 evolution.
• Electrolyte degradation produced gaseous and protic species.
• Higher fluorine content led to increased fluorine dissolution from the DRX material.
• Manganese and fluorine dissolution from the DRX material occurred at high voltages.

Conclusions:

• Fluorine content influences interfacial degradation pathways in DRX cathodes.
• Manganese and fluorine dissolution are key degradation mechanisms at high voltages.
• Understanding these processes is crucial for developing stable DRX materials for Li-ion batteries.