Beyond Half-Cell Success: Cathode-Electrolyte Reactivity Driving Magnesium Battery Full-Cell Degradation at Elevated...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Rechargeable magnesium batteries (RMBs) are explored as a sustainable alternative to lithium-ion batteries due to magnesium's abundance and high theoretical capacity.
• Challenges persist in achieving stable, high-voltage RMB full cells, particularly concerning electrode-electrolyte interface stability.

Purpose of the Study:

• To investigate the performance and degradation mechanisms of a vanadium oxide (VO2) cathode in a rechargeable magnesium battery full cell.
• To evaluate the impact of temperature on the stability and cycling performance of the RMB full cell.

Main Methods:

• Fabrication and electrochemical testing of a RMB full cell using a VO2 cathode and a weakly coordinating anion-based electrolyte.
• Half-cell and full-cell performance evaluation at different temperatures (30°C and 60°C).
• Three-electrode measurements and post-mortem analysis to identify degradation pathways.

Main Results:

• The RMB full cell exhibited initial discharge capacities but showed significant capacity fade at 60°C (77 mAh g⁻¹ to 28 mAh g⁻¹ in the second cycle).
• Performance at 30°C was more stable, retaining approximately 25 mAh g⁻¹.
• Three-electrode tests indicated increasing overpotentials at the magnesium anode, linked to uneven plating/stripping and surface degradation.

Conclusions:

• Elevated temperatures exacerbate capacity degradation in VO2-based RMB full cells, primarily due to anode overpotentials and cathode-electrolyte side reactions.
• Issues like uneven magnesium plating, surface pitting, and minor vanadium dissolution contribute to impedance growth.
• Developing robust interphases is crucial for enhancing the long-term cyclability of RMB full cells, especially for high-temperature applications.