Free-standing Li⁺-conductive films based on PEO-PVDF blends

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Science

Background:

• Solid electrolytes are crucial for all-solid-state batteries, offering enhanced safety and energy density.
• Existing polymer electrolytes often face challenges with mechanical stability or ionic conductivity.
• The LiTFSI-PEO system exhibits a 'crystallinity gap' hindering the formation of mechanically robust, conductive solid electrolytes.

Purpose of the Study:

• To fabricate improved solid electrolyte membranes using LiTFSI and PEO-PVDF blends.
• To investigate the effect of PVDF addition on the mechanical and ionic properties of LiTFSI-PEO electrolytes.
• To understand the structural and chemical interactions within the PEO-PVDF-LiTFSI system.

Main Methods:

• Fabrication of free-standing electrolyte membranes from PEO-PVDF blends with LiTFSI.
• Characterization using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC).
• Ionic conductivity measurements at various temperatures.
• Density functional theory (DFT) calculations to assess Li+ complexation energies.

Main Results:

• Addition of PVDF allows the formation of stable, free-standing films within the LiTFSI-PEO 'crystallinity gap'.
• Optimal PVDF content yields membranes with a reasonable elastic modulus and high ionic conductivity (0.3 mS cm⁻¹ at 60 °C, 0.1 mS cm⁻¹ at room temperature).
• PVDF remains partially crystalline, enhancing mechanical properties and promoting LiTFSI dissociation and polymer chain disordering.

Conclusions:

• PEO-PVDF blends offer a promising strategy for developing mechanically stable and ionically conductive solid electrolytes.
• The synergistic effect of PVDF enhances salt dissociation and mechanical integrity without significantly compromising ionic conductivity.
• These findings pave the way for advanced all-solid-state electrochemical energy storage devices.