Deciphering Structural Origins of Highly Reversible Lithium Storage in High Entropy Oxides with In Situ Transmission...

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Configurational entropy-stabilized high-entropy oxides (HEOs) show promise as advanced electrode materials.
• Simultaneously achieving reversible lithium storage and high specific capacity is challenging for conventional electrodes.
• The precise lithium storage mechanisms in complex multi-cationic HEOs are not fully understood.

Purpose of the Study:

• To investigate the reaction dynamics and structural evolution of rocksalt-type HEOs during lithium cycling.
• To elucidate the composition-dependent lithium storage mechanisms and valence state changes.
• To provide insights into designing HEOs for next-generation energy storage.

Main Methods:

• In situ transmission electron microscopy (TEM) for atomic-scale imaging, electron diffraction, and electron energy loss spectroscopy.
• Electrochemical testing.
• Postmortem ex situ TEM and bulk-level phase analyses.

Main Results:

• Distinct lithiation mechanisms, including conversion/alloying reactions and spatiotemporal valence state variations, were observed, leading to the disappearance of the rocksalt phase.
• The post-lithiation polyphase state was found to reversibly recover to the original rocksalt-structured HEOs during delithiation.
• This structural recovery capability, unique to HEOs compared to monometallic oxides, is crucial for high-capacity, reversible lithium storage.

Conclusions:

• The study reveals the detailed mechanisms of lithium storage and structural evolution in HEOs at the atomic scale.
• The reversible structural recovery of HEOs is key to their high-capacity and long-life performance in lithium storage.
• These findings offer valuable guidelines for the rational design of HEOs as superior electrode materials for advanced energy storage devices.