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Hydroxyl Defects in LiFePO4 Cathode Material: DFT+U and an Experimental Study
Dmitry A Aksyonov1, Irina Varlamova1, Ivan A Trussov1
1Skolkovo Institute of Science and Technology, 121205 Moscow, Russian Federation.
Inorganic Chemistry
|April 8, 2021
Summary
This study reveals complex OH point defects in lithium iron phosphate (LiFePO₄) cathode materials. These defects influence vacancy stabilization and P-site deficiency, impacting Li-ion battery performance.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Computational Materials Science
Background:
- Lithium iron phosphate (LiFePO₄) is a key cathode material for Li-ion batteries.
- Its defect structure is complex and not fully understood, impacting performance.
Purpose of the Study:
- To comprehensively characterize OH point defects in LiFePO₄.
- To investigate their formation, dynamics, and impact on vacancies and site occupancies.
Main Methods:
- Combined computational (DFT+U, molecular dynamics) and experimental (X-ray/neutron diffraction) approaches.
- Structure refinement at 5 K for deuterium-enriched LiFePO₄.
Main Results:
- OH groups stabilize Li, Fe, and P vacancies.
- Confirmed presence of D/H at Li and P sites, with 6% P deficiency.
- Identified hydrogarnet-like P/4H and P/5H defects as lowest energy OH defects.
- MD simulations revealed diverse OH defect conformers, including structural water molecules.
Conclusions:
- OH defects significantly influence LiFePO₄'s defect chemistry and structure.
- The P deficiency is attributed to specific hydrogarnet-like OH defects.
- Defect complexity, including conformers, challenges precise localization via diffraction alone.
