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Formation of LiF Surface Layer During Direct Fluorination of High-Capacity Co-Free Disordered Rocksalt Cathodes
Yiman Zhang1, Ethan C Self1, Bishnu P Thapaliya2
1Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
ACS Applied Materials & Interfaces
|August 4, 2021
Summary
Direct fluorination of disordered rocksalt (DRX) cathodes creates LiF surface films, enhancing specific energy and capacity retention. This method improves electrochemical performance in high-voltage cathode materials.
Area of Science:
- Materials Science
- Electrochemistry
- Solid-state Chemistry
Background:
- Disordered rocksalt (DRX) cathodes offer high capacity and compositional flexibility, including cobalt-free options.
- However, sloping voltage profiles and capacity fade limit their practical application.
- Fluorine substitution is theoretically predicted to enhance DRX cathode performance.
Purpose of the Study:
- To investigate the impact of fluorine content on the structure and electrochemical performance of a model Li-rich DRX cathode.
- To explore direct fluorination as a strategy to improve cathode properties.
Main Methods:
- Utilized a fluidized bed reactor for direct fluorination of a Li-rich disordered rocksalt (DRX) composition (Li1.15Ni0.375Ti0.375Mo0.1O2, NTMO).
- Analyzed structural changes and electrochemical performance after fluorination.
Main Results:
- Direct fluorination resulted in the formation of LiF surface films, rather than oxygen-fluorine substitution.
- The LiF surface films improved specific energy and capacity retention of the NTMO cathode.
- Electrochemical performance of the high-voltage cathode was enhanced.
Conclusions:
- Direct fluorination is a feasible method to improve the electrochemical performance of disordered rocksalt (DRX) cathodes.
- Tuning surface chemistry via LiF film formation is key to enhancing high-voltage cathode materials.
- This approach offers a pathway to more stable and higher-performing battery cathodes.
