Ultrahigh-Loading Manganese-Based Electrodes for Aqueous Batteries via Polymorph Tuning

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Manganese-based aqueous batteries offer safe, low-cost grid-scale energy storage.
• Low conductivity of deposited manganese dioxide (MnO2) limits areal loading and performance.
• Current areal loading in MnO2 batteries is typically 0.005-0.05 mAh cm⁻².

Purpose of the Study:

• Investigate electrochemical performance of MnO2 polymorphs in Mn2+/MnO2 redox reactions.
• Identify strategies to overcome conductivity limitations in MnO2 electrodes.
• Achieve ultrahigh areal loading for improved energy storage capacity.

Main Methods:

• Electrochemical performance testing of various MnO2 polymorphs.
• Phase analysis of electrochemically deposited MnO2 at different temperatures.
• Electrode fabrication and cycling at elevated temperatures (50°C).

Main Results:

• Epsilon-MnO2 (ɛ-MnO2) with low conductivity is the primary phase deposited in acidic electrolytes.
• Increasing temperature shifts deposition to gamma-MnO2 (γ-MnO2), improving conductivity by two orders of magnitude.
• Achieved normalized areal loading of 33 mAh cm⁻² with γ-MnO2.
• Demonstrated ultrahigh areal loading of 20 mAh cm⁻² at 50°C with only 13% capacity loss over 200 cycles.

Conclusions:

• Temperature-dependent phase transformation is key to enhancing MnO2 conductivity.
• Highly conductive γ-MnO2 enables significantly higher areal loading in aqueous batteries.
• This approach offers a promising pathway for advanced grid-scale energy storage solutions.