Probing MnO₂ Cycling Stability in Aqueous Zinc-Ion Batteries using Chemical Strain Analysis

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Mechanical degradation of cathodes limits the cycle life of aqueous zinc-ion batteries (AZIBs).
• The reaction mechanisms and mechanical evolution of MnO2 cathodes during cycling are poorly understood.
• Understanding these processes is crucial for developing stable AZIBs.

Purpose of the Study:

• To comprehensively investigate the electrochemical phase transitions and chemical strain evolution in δ-MnO2 cathodes during charge-discharge cycling.
• To elucidate the underlying mechanisms of mechanical degradation.
• To identify strategies for enhancing electrode cycling stability.

Main Methods:

• Utilized a custom-built in situ strain testing system.
• Employed digital image correlation for precise strain measurement.
• Performed electrochemical cycling of δ-MnO2 cathodes.

Main Results:

• Discharge-charge mechanism involves initial cointercalation of H+ and Zn2+ leading to elastic deformation.
• Phase transformation to ZnMn2O4 occurs during discharge.
• Charging induces irreversible plastic deformation and volume expansion due to phase transformation and ZnMn3O7 formation.
• Increasing current density suppresses phase transformation and reduces residual strain.

Conclusions:

• The study reveals the detailed mechanism of mechanical degradation in δ-MnO2 cathodes.
• Residual strain and volume expansion are linked to phase transformations during cycling.
• Optimizing current density is a viable strategy to enhance the cycling stability of AZIBs.