Cathode Electrolyte Interphase (CEI) Endows Mo₆ S₈ with Fast Interfacial Magnesium-Ion Transfer Kinetics

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Magnesium (Mg) metal secondary batteries offer high safety and energy density.
• The cathode/electrolyte interphase (CEI) is a critical but often overlooked component in Mg battery performance.
• Understanding and controlling the CEI is essential for advancing Mg battery technology.

Purpose of the Study:

• To construct a novel CEI layer on a Mo₆ S₈ cathode.
• To investigate the composition and function of the newly formed CEI.
• To elucidate the impact of the CEI on Mg²⁺ ion transfer and storage.

Main Methods:

• Electrochemical synthesis of CEI using Mg[B(hfip)₄ ]₂ salt.
• Characterization of the CEI composition, identifying B_x O_y species.
• Evaluation of Mg²⁺ desolvation and interfacial transfer kinetics.

Main Results:

• A stable CEI layer was successfully formed on the Mo₆ S₈ cathode surface.
• The CEI was found to contain beneficial B_x O_y species derived from the electrolyte salt.
• The B_x O_y species facilitated Mg²⁺ desolvation and improved interfacial transfer kinetics.
• Enhanced Mg²⁺ storage capability of the Mo₆ S₈ cathode was demonstrated.

Conclusions:

• The study presents the first reported CEI construction in Mg batteries.
• The findings highlight the crucial role of the CEI in improving Mg battery performance.
• This work provides valuable insights into interfacial phenomena in multivalent electrochemical systems.