Negative thermal expansion and oxygen-redox electrochemistry

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Physics

Background:

• Structural disorder in materials influences thermodynamic and electrochemical properties.
• Oxygen-redox (OR) electrochemistry enhances capacity but can reduce reversibility and induce disorder.
• Conventional thermal expansion models (Grüneisen relationship) may not apply to OR materials due to dynamic disorder-order transitions.

Purpose of the Study:

• To investigate thermal expansion behavior in OR active materials.
• To explore the link between disorder-order transitions and thermal expansion.
• To establish a framework for designing materials with tunable thermal expansion, including zero thermal expansion.

Main Methods:

• Experimental characterization of OR active materials.
• Analysis of thermal expansion coefficients.
• Electrochemical cycling to induce and reverse structural disorder.
• Operando electrochemical processes for material restoration.

Main Results:

• Discovery of significant negative thermal expansion (-14.4(2) × 10⁻⁶ °C⁻¹) in OR materials, attributed to thermally driven disorder-order transitions.
• Demonstration that OR behavior modulation precisely controls thermal expansion.
• Successful reinstatement of structural disorder via electrochemical driving force, achieving nearly 100% structure recovery by adjusting cut-off voltages.

Conclusions:

• Thermally driven disorder-order transitions are responsible for negative thermal expansion in OR materials.
• Electrochemical control over OR behavior allows for precise tuning of thermal expansion.
• Operando electrochemical processes can restore OR active materials, mitigating voltage decay and offering a pathway for material longevity.