Hydrated Eutectic Electrolytes Stabilizing Quasi-Underpotential Mg Plating/Stripping for High-Voltage Mg Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Aqueous rechargeable magnesium batteries (ARMBs) commonly suffer from anode passivation, limiting their practical application.
• Quasi-underpotential magnesium plating/stripping chemistry (UPMC) on heterogeneous metal substrates offers a potential solution to mitigate passivation issues.

Purpose of the Study:

• To develop a stable UPMC on a zinc (Zn) substrate within novel hydrated eutectic electrolytes (HEEs).
• To investigate the electrochemical performance and stability of UPMC in ARMBs.
• To demonstrate the potential of UPMC-based ARMBs for high-energy storage applications.

Main Methods:

• Development and characterization of new hydrated eutectic electrolytes (HEEs).
• Implementation of quasi-underpotential magnesium plating/stripping chemistry (UPMC) on a zinc substrate.
• Electrochemical testing of UPMC stability and performance, including overpotential and cycling life.
• Fabrication and evaluation of full cells using UPMC anodes and sulfonic acid-doped polyaniline (SPANI) cathodes.

Main Results:

• Achieved stable UPMC on a Zn substrate in HEEs with an ultralow overpotential (50 mV at 0.1 mA cm⁻² over 550 h).
• The unique eutectic properties of HEEs expanded the electrochemical stability window (ESW) and suppressed hydrogen evolution/corrosion.
• UPMC-based full cells with SPANI cathodes exhibited high energy/power densities (168.6 Wh kg⁻¹ / 2.1 kWh kg⁻¹) and a 1.3 V voltage plateau.

Conclusions:

• Stable UPMC on Zn substrates in novel HEEs is a viable strategy to overcome anode passivation in ARMBs.
• The developed electrolytes and UPMC approach significantly enhance the electrochemical performance of ARMBs.
• This work paves the way for high-performance and stable aqueous rechargeable magnesium batteries.