Evolution of the Dynamic Solid Electrolyte Interphase in Mg Electrolytes for Rechargeable Mg-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• The solid electrolyte interphase (SEI) at the magnesium (Mg) anode-electrolyte interface is crucial for Mg-ion battery performance but poorly understood.
• Compatibility challenges at the Mg anode-electrolyte interface hinder the development of high-performance Mg-ion batteries.

Purpose of the Study:

• To investigate the formation and evolution of the SEI at the Mg electrolyte/electrode interface under different electrolyte conditions.
• To elucidate the mechanisms governing SEI behavior and its impact on Mg anode reversibility and battery performance.

Main Methods:

• In situ electrochemical quartz crystal microbalance with dissipation mode (EQCM-D)
• Electrochemical impedance spectroscopy (EIS)
• Field emission scanning electron microscopy (FESEM)
• Energy-dispersive X-ray spectroscopy (EDS)
• Fourier transform infrared spectrometry (FTIR)

Main Results:

• Two distinct SEI evolution pathways were observed for a non-halogen Mg(TFSI)2 in THF with DMA (nhMg-DMA) electrolyte and a halogen-containing all-phenyl complex (APC) electrolyte.
• The nhMg-DMA electrolyte showed minimal SEI formation initially, followed by complex growth and improved Mg deposition with a MgF2-rich interface.
• The APC electrolyte exhibited initial extensive SEI formation, followed by dissolution, SEI stabilization, and improved charge transport kinetics with high-purity Mg deposition.

Conclusions:

• Electrolyte composition significantly dictates SEI formation, evolution, and stability at the Mg anode.
• Understanding these interfacial dynamics is critical for designing stable Mg anodes and advancing Mg-ion battery technology.
• The study provides insights into optimizing electrolyte formulations for enhanced Mg deposition and overall battery performance.