Oxygen-Loss-Induced Structural Degradation in ε-LiVOPO₄

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• ε-LiVOPO₄ is a promising cathode material for lithium-ion batteries due to its high capacity.
• Structural degradation caused by oxygen loss is a critical issue for cathode performance but remains understudied.
• Understanding oxygen loss mechanisms is crucial for developing stable and durable battery materials.

Purpose of the Study:

• To investigate the atomic-scale mechanisms of lattice oxygen loss in ε-LiVOPO₄ cathodes.
• To reveal the structural dynamics and phase transformation pathways induced by oxygen loss.
• To explore strategies for mitigating structural degradation in oxide cathodes.

Main Methods:

• Utilized *in situ* environmental transmission electron microscopy (ETEM) to observe structural changes at the atomic scale.
• Spatially and temporally resolved lattice oxygen loss and phase transformations.
• Investigated the effects of varying temperatures (400 °C, 500 °C, 600 °C) on structural integrity.

Main Results:

• Mild oxygen loss at 400 °C triggered a reversible topotactic phase transformation (ε-LiVOPO₄ → α-Li₃V₂(PO₄)₃) via nucleation and growth, forming a core-shell structure.
• Reversible transformation was achieved by switching to an oxidizing environment.
• Severe oxygen loss at 500 °C and 600 °C resulted in irreversible structural damage, including amorphization and nanocavity formation due to high oxygen vacancy concentration.

Conclusions:

• Demonstrated that oxygen loss is a key factor in the structural degradation of ε-LiVOPO₄ cathodes.
• Identified distinct degradation mechanisms at different temperatures, highlighting the role of oxygen vacancies.
• Proposed that controlling environmental conditions can be a strategy to manage structural stability and enhance cathode performance.