Dilute Electrolyte with Vehicular Aggregates for Stable High-Energy Lithium-Metal Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Electrolyte design is crucial for lithium-metal batteries (LMBs), impacting the solid-electrolyte interphase (SEI), cycling stability, and Coulombic efficiency (CE).
• Conventional concentrated electrolytes achieve good lithium-metal compatibility via anion-solvent-Li+ aggregates (AGG) but suffer from low ionic conductivity (≈1 mS cm−1).
• A key challenge is achieving both high ionic conductivity and AGG-dominated solvation under dilute conditions for improved LMB performance.

Purpose of the Study:

• To propose a novel dilute electrolyte with vehicular aggregates (DVA) mechanism for high-energy LMBs.
• To investigate the solvation structure and ion transport mechanism in the DVA electrolyte.
• To evaluate the electrochemical performance of the DVA electrolyte in 4.6-V-class LMBs with ultra-high-Ni cathodes.

Main Methods:

• Development of a dilute electrolyte using pyrrolidine-1-sulfonyl fluoride (PSF) solvent with optimal steric hindrance.
• Characterization of the electrolyte's solvation structure and ion transport properties.
• Electrochemical testing of LMBs with ultra-high-Ni cathodes using the developed DVA electrolyte, including cycling stability, rate capability, and CE measurements.

Main Results:

• The DVA electrolyte exhibits a unique AGG-dominated solvation structure under dilute conditions, achieving high ionic conductivity (4.9 mS cm−1) via a vehicular ion-transport mechanism.
• Excellent lithium-metal compatibility was observed, with a high stripping-plating CE of ≈99.5% and the formation of an inorganic (LiF, Li2O)-rich robust SEI.
• The electrolyte effectively suppressed detrimental side reactions, enabling LMBs to deliver a high discharge capacity (228.4 mAh g−1), excellent rate capability (up to 2C), and 87% capacity retention after 150 cycles.

Conclusions:

• The proposed DVA electrolyte successfully addresses the challenge of achieving high ionic conductivity and stable lithium-metal compatibility under dilute conditions.
• This approach offers a promising strategy for designing advanced electrolytes for high-energy lithium-metal batteries.
• The developed electrolyte demonstrates significant potential for enabling next-generation energy storage devices with enhanced performance and longevity.