Anisotropic Ion Diffusion and Electrochemically Driven Transport in Nanostructured Block Copolymer Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Science

Background:

• Solid-state batteries offer enhanced safety and energy density compared to conventional lithium-ion batteries.
• Nanostructured block copolymers are promising electrolytes for enabling solid-state batteries with lithium metal anodes.
• Understanding ion transport mechanisms within these electrolytes is crucial for optimizing battery performance.

Purpose of the Study:

• To characterize ion transport in a lamellar polystyrene-b-poly(ethylene oxide) copolymer/lithium bis(trifluoromethanesulfonyl)imide electrolyte.
• To investigate the influence of salt concentration on ion transport properties.
• To correlate ion diffusion characteristics with the nanostructure and defect density of the electrolyte.

Main Methods:

• Electrochemical measurements to determine Stefan-Maxwell salt diffusion coefficients.
• Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) to measure individual self-diffusion coefficients.
• Transmission electron microscopy (TEM) to visualize electrolyte morphology and defect density.

Main Results:

• Salt diffusion within the block copolymer electrolyte is locally anisotropic.
• An NMR morphology factor quantifying anisotropic diffusion was correlated with defect density observed via TEM.
• Agreement was found between electrochemically determined diffusion coefficients and PFG-NMR derived diffusion coefficients through defects (D⊥).

Conclusions:

• Ion transport through defects in nanostructured block copolymer electrolytes is a critical factor influencing their performance in batteries.
• The study provides a comprehensive characterization of ion transport, linking molecular-level diffusion to macroscopic electrochemical properties.
• This research offers insights for designing improved solid-state electrolytes for next-generation batteries.