Mixed-Coordination Electrolytes With Molecular Additives for Robust Interphases in High-Voltage Rechargeable...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Rechargeable magnesium batteries (RMBs) present a promising low-cost, high-capacity energy storage solution.
• High-voltage operation in RMBs is hindered by electrolyte oxidative decomposition, limiting energy density and stability.
• Conventional ether-based electrolytes struggle with stable performance at elevated voltages.

Purpose of the Study:

• To develop a novel electrolyte system for stable high-voltage operation in RMBs.
• To introduce a mixed-coordination electrolyte (MCE) with a molecular additive (MCE-MA) for improved interphase formation and cycling stability.
• To investigate the mechanisms behind enhanced performance using advanced surface analysis techniques.

Main Methods:

• Formulation of a mixed-coordination electrolyte (MCE) integrating dissociative and associative coordinating salts.
• Incorporation of a molecular additive (MCE-MA) to promote robust interphase development.
• Electrochemical evaluation using Cu|Mg asymmetric and Mg|Mg symmetric cells, and full cells with oxide cathodes.
• Surface characterization using X-ray photoelectron spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

Main Results:

• MCE-MA demonstrated improved Mg plating/stripping efficiency in asymmetric cells.
• Sustained over 250 hours of stable cycling in Mg|Mg symmetric cells, outperforming conventional electrolytes.
• Enabled long-term cycling of a full cell with an oxide cathode, achieving 200 cycles at 100 mA g⁻¹.
• Surface analysis revealed the formation of uniform, anion-derived interphases.

Conclusions:

• The MCE-MA system effectively enhances cycling stability and performance in high-voltage RMBs.
• The optimized electrolyte promotes the formation of protective anion-derived interphases crucial for battery longevity.
• This work provides a viable pathway towards practical high-energy-density rechargeable magnesium batteries.