Mechanically stable polymer networks incorporating polymeric ionic liquids for enhanced conductivity in solid-state...

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Designing solid-state electrolytes for lithium batteries faces challenges in balancing ionic conductivity and mechanical strength.
• Existing electrolytes often exhibit trade-offs between flexibility and ion transport efficiency.

Purpose of the Study:

• To develop mechanically robust and highly conductive solid-state electrolytes for lithium batteries.
• To create novel polymer networks incorporating polymeric ionic liquids (PILs) for enhanced performance.

Main Methods:

• Synthesis of linear PILs with varying side groups and molecular weights (30-40 kDa) determined by thermal field-flow fractionation (ThFFF) and MALDI-TOF MS.
• Photo-initiated polymerization to create cross-linked membranes (semi-interpenetrating networks) using a monomer, cross-linker, LiTFSI, and PILs with quaternized imidazolium groups.
• Characterization of mechanical properties (Young's modulus of 40-50 MPa) and ionic conductivity (4 × 10⁻⁴ S·cm⁻¹ at 60°C).

Main Results:

• Developed cross-linked membranes with Young's modulus of 40-50 MPa, exceeding requirements for solid-state battery separators.
• Achieved high ionic conductivity (4 × 10⁻⁴ S·cm⁻¹ at 60°C) by incorporating PILs into the polymer network.
• Demonstrated that oligo(ethylene glycol) moieties in PILs enhance ionic conductivity and lithium salt incorporation compared to alkyl-substituted analogs.

Conclusions:

• The developed semi-interpenetrating polymer networks offer a promising solution for solid-state lithium battery electrolytes.
• These materials effectively address the trade-off between mechanical robustness and ionic conductivity.
• The novel approach using ionic liquid-based cross-linked polymer networks paves the way for advanced battery technologies.