Investigating Crystallization and Morphology of PLLA/PTMC Triblock Copolymer Solid Electrolytes

Area of Science:

• Polymer Science and Engineering
• Materials Science
• Electrochemistry

Background:

• Solid polymer electrolytes (SPEs) are crucial for advanced battery technologies.
• ABA-type block copolymers (BCPs) offer tunable properties for electrolyte applications.
• Poly(l-lactic acid) (PLLA) and poly(trimethylene carbonate-co-trimethylene ether) (PTMC-co-PTME) are promising BCP components.

Purpose of the Study:

• To synthesize and characterize ABA-type BCPs of PLLA and PTMC-co-PTME.
• To investigate the formation and properties of SPEs by blending BCPs with lithium bis-(trifluoro methylsulfonate) (LiTFSI).
• To elucidate the relationship between BCP self-assembly, crystallization kinetics, phase behavior, and ionic conductivity.

Main Methods:

• Ring-opening polymerization for BCP synthesis.
• Electrochemical impedance spectroscopy for ionic conductivity measurements (30–150 °C).
• Simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) for structural and crystallization analysis.

Main Results:

• PLLA-b-PTMC-co-PTME-b-PLLA BCPs exhibit hierarchical organization with spherulitic superstructures.
• PLLA crystallization is the primary driver for micro- and nanoscale self-assembly.
• Increased LiTFSI content slowed PLLA crystallization and altered crystalline phase, slightly reducing ionic conductivity.

Conclusions:

• The hierarchical self-assembly of ABA BCPs is governed by PLLA crystallization, influencing SPE microstructure.
• LiTFSI concentration impacts crystallization kinetics and phase composition, affecting ionic conductivity.
• An SPE with 20 wt % LiTFSI achieved a conductivity of 1.2 × 10⁻⁶ S cm⁻¹ at 60 °C.