Enabling Magnesium Anodes by Tuning the Electrode/Electrolyte Interfacial Structure.

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Magnesium (Mg)-ion batteries offer high theoretical capacity but suffer from poor reversibility due to Mg anode surface passivation.
• Electrolyte anion reduction, specifically bis(trifluoromethanesulfonyl)imide (TFSI^-), is a primary cause of this passivation layer formation.
• This limits the electrochemical performance and practical application of Mg-ion batteries.

Purpose of the Study:

• To introduce a new deposition mechanism for highly reversible Mg plating and stripping in Mg-ion batteries.
• To investigate the role of sodium cations (Na⁺) in altering the interfacial chemistry of Mg anodes.
• To suppress the decomposition of TFSI^- anions and prevent passivation layer formation.

Main Methods:

• Molecular dynamics simulations to understand cation interactions at the Mg anode interface.
• Electrochemical analyses (plating/stripping) to evaluate reversibility and overpotential.
• Microscopic and spectroscopic techniques to characterize the Mg anode surface morphology and composition.

Main Results:

• Molecular dynamics simulations indicated that Na⁺ cations form a significant population in the interfacial double layer, excluding TFSI^- anions.
• This exclusion effectively suppressed TFSI^- decomposition and the formation of passivation layers on the Mg surface.
• Electrochemical and surface analyses confirmed smoother Mg deposition morphology and reduced overpotentials compared to electrolytes without Na⁺.

Conclusions:

• The addition of Na⁺ to Mg-ion electrolytes fundamentally alters interfacial chemistry, enabling reversible Mg plating and stripping.
• This Na⁺-mediated mechanism effectively prevents Mg anode passivation by suppressing anion decomposition.
• The findings present a promising strategy for developing high-performance Mg-ion batteries.