A Super-Ionic Solid-State Block Copolymer Electrolyte

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Science

Background:

• Polymer solid-state electrolytes are promising for high-energy-density batteries due to safety and stability.
• Low ion conductivity in these materials has hindered their practical application.
• Developing electrolytes with high ionic conductivity is crucial for next-generation battery technology.

Purpose of the Study:

• To investigate the effect of super-stoichiometric lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) addition on poly(ethylene oxide) (PEO) block copolymer electrolytes.
• To achieve high ionic conductivities and low activation energies in solid polymer electrolytes.
• To explore novel morphologies and conduction pathways in PEO-based electrolytes.

Main Methods:

• Synthesis and characterization of PEO block copolymers with varying LiTFSI concentrations.
• Electrochemical impedance spectroscopy to measure ionic conductivity and activation energy.
• Microscopy techniques to analyze block copolymer morphologies and phase transitions.

Main Results:

• Super-stoichiometric LiTFSI addition induced crystalline PEO block copolymer phases.
• Formation of bi-continuous Fddd and gyroid network morphologies facilitated 3D ion conduction pathways.
• Achieved ionic conductivities up to 1 x 10^-1 S cm^-1 at 90°C, with moderate conductivity at room temperature (4 x 10^-2 S cm^-1) and low temperatures (>1 x 10^-3 S cm^-1 at -20°C).
• Observed low activation energies as low as 0.19 eV.
• Co-crystallization of PEO and LiTFSI with solvents was identified as key to super-ionic conduction.

Conclusions:

• The study demonstrates a new pathway to achieve super-ionic conductivity in PEO-based solid polymer electrolytes.
• High lithium salt concentrations and resulting crystalline phases are critical for enhanced ionic transport.
• These findings pave the way for fabricating advanced solid polymer electrolytes with broad-temperature performance for electrical devices.