High-Performance Magnesium Electrochemical Cycling with Hybrid Mg-Li Electrolytes

Area of Science:

• Electrochemistry
• Materials Science
• Inorganic Chemistry

Background:

• Electrochemical magnesium plating and stripping are crucial for energy storage.
• Electrolyte composition significantly impacts magnesium cycling performance.
• Passivation of magnesium surfaces hinders efficient electrochemical processes.

Purpose of the Study:

• To systematically investigate Mg^0/2+ electrochemical cycling in various Mg²⁺-Li⁺-borohydride-bis(trifluoromethylsulfonyl)imide (TFSI^-) electrolytes.
• To identify electrolyte compositions that enhance coulombic efficiency and deposition/stripping rates.
• To understand the role of different ionic species in preventing magnesium surface passivation.

Main Methods:

• Electrochemical studies (plating/stripping) in 1,2-dimethoxyethane (DME) solvent.
• Systematic variation of electrolyte components: Mg²⁺, Li⁺, BH₄^-, and TFSI^-.
• Spectroscopic analysis (Raman and NMR) to confirm ion coordination.

Main Results:

• The presence of BH₄^- is essential for high coulombic efficiency.
• Li⁺ and TFSI^- are required for high deposition/stripping rates.
• The Li⁺ + BH₄^- + TFSI^- combination effectively prevents magnesium surface passivation.
• An optimal [Mg(BH₄)₂]:[LiTFSI] mole ratio of 1:2 yielded stabilized coulombic efficiency of 88 ± 1%.

Conclusions:

• The optimized electrolyte enables efficient Mg^0/2+ electrochemical cycling.
• This electrolyte system demonstrates high coulombic efficiency and deposition/stripping rates at ambient temperature.
• The findings provide a pathway for developing advanced magnesium-based electrochemical systems.