Anion π-π Stacking for Improved Lithium Transport in Polymer Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Polymer electrolytes (PEs) offer flexibility and processability for lithium metal (Li°) batteries.
• Conventional poly(ethylene oxide) (PEO)-based PEs exhibit low lithium-ion transference numbers (T_Li⁺), causing concentration gradients and cell polarization.
• Developing PEs with high T_Li⁺ and selective ion conductivity is crucial for advanced batteries.

Purpose of the Study:

• To develop novel solvent-free PEs with enhanced lithium-ion transference numbers and conductivity.
• To investigate the role of benzene-based lithium salts in improving PE performance.
• To explore a new molecular design strategy for high-performance solid-state electrolytes.

Main Methods:

• Synthesis and characterization of novel benzene-based lithium salts: lithium (benzenesulfonyl)(trifluoromethanesulfonyl)imide (LiBTFSI) and lithium (2,4,6-triisopropylbenzenesulfonyl)(trifluoromethanesulfonyl)imide (LiTPBTFSI).
• Fabrication of solvent-free PEs using LiBTFSI and LiTPBTFSI with PEO.
• Molecular dynamics (MD) simulations to elucidate the mechanism of improved ion transport.
• Electrochemical performance testing of Li°∥Li° and Li°∥LiFePO₄ cells.

Main Results:

• The novel PEs exhibited significantly improved T_Li⁺ and selective lithium-ion conductivity compared to conventional PEs.
• MD simulations revealed that strong π-π stacking interactions between benzene-based anions are responsible for the enhanced ion transport.
• LiBTFSI/PEO electrolytes demonstrated enhanced cycling performance in Li°∥Li° and Li°∥LiFePO₄ cells.
• The developed PEs offer a promising alternative to liquid electrolytes for safer and more efficient batteries.

Conclusions:

• Benzene-based lithium salts, through π-π stacking interactions, provide an effective strategy for designing highly selective lithium-ion conductive polymer electrolytes.
• This work presents a facile and efficient molecular-level design route for advanced solid-state electrolytes.
• The findings pave the way for developing next-generation lithium-ion batteries with improved safety and performance.