Understanding the Tunnel-Structured Evolution in α-MnO₂ Cathode Failure for Aqueous Zinc Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Aqueous Zn-Mn batteries offer safety and cost benefits.
• Understanding hollandite cathode failure mechanisms is crucial for performance improvement.

Purpose of the Study:

• To investigate the tunnel-structured evolution of α-MnO2 during electrochemical cycling.
• To elucidate the failure mechanisms of hollandite cathodes in aqueous Zn-Mn batteries.

Main Methods:

• Monitoring tunnel-structured evolution of α-MnO2.
• Utilizing Ca- and Cr-doped α-MnO2 as cathode materials.
• Employing ex situ X-ray near-edge absorption spectroscopy.

Main Results:

• Ca-MnO2 and Cr-MnO2 show expanded tunnel dimensions, improving charge transfer and ion diffusion.
• Ca-MnO2 exhibits a breathable structure, tolerating cation insertion/extraction and enhancing stability.
• Cr-MnO2's rigid expanded structure hinders repeated structural changes, leading to failure.

Conclusions:

• The breathable tunnel structure of Ca-MnO2 significantly enhances cycle stability and kinetics while suppressing Mn dissolution.
• α-MnO2 cathodes suffer structural collapse due to their inherent or rigid structures, resulting in rapid capacity fading.
• Insights into α-MnO2 cathode failure guide the design of durable hollandite cathodes for rechargeable batteries.