Thermally Induced Interfacial Changes of Solid Polymer Electrolytes in Electric Double-Layer Supercapacitors

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Science

Background:

• Solid-state supercapacitors offer potential for flexible electronics.
• Replacing liquid electrolytes with solid polymer electrolytes (SPEs) often leads to reduced capacitance and energy density.
• The electrode-electrolyte interface, often overlooked, may be a critical factor limiting performance.

Purpose of the Study:

• To investigate the impact of polymer morphology and interfacial contact on the electrochemical performance of SPEs.
• To compare the performance of PEO, PLA, and PMMA-based SPEs with identical thermal histories.
• To determine whether ionic conductivity or interfacial stability is the dominant factor in supercapacitor performance.

Main Methods:

• Investigated PEO, PLA, and PMMA-based SPEs (20 wt % lithium salt).
• Performed temperature-dependent ionic conductivity measurements.
• Assessed interfacial capacitance and morphological stability under various thermal treatments (as-cast, rapid cooling, slow cooling).

Main Results:

• Ionic conductivity followed Arrhenius behavior, with PEO > PMMA > PLA.
• As-cast films showed poor electrode contact (<1 μF/cm²).
• Rapid cooling enhanced interfacial capacitance (~35 μF/cm²) by replicating electrode morphology.
• Crystallization in PEO and PLA upon slow cooling reduced capacitance, while amorphous PMMA maintained stable capacitance (~10.2-10.4 μF/cm²).

Conclusions:

• Interfacial capacitance stability is directly linked to the morphological stability of the SPE, not solely bulk ionic conductivity.
• Amorphous polymers like PMMA offer advantages for durable electrode-electrolyte contact in supercapacitors.
• Interfacial engineering and control of polymer phase behavior are crucial for developing high-performance, next-generation SPE-based energy storage devices.