Dynamic Structure and Phase Behavior of a Block Copolymer Electrolyte under dc Polarization

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Science

Background:

• Designing advanced lithium battery electrolytes requires understanding ion transport during fast charge/discharge.
• High current densities induce significant salt concentration gradients.
• Nanostructured composite electrolytes are promising for high-energy lithium metal anodes, but their morphological response to gradients is unclear.

Purpose of the Study:

• To investigate the interplay between nanostructure morphology and salt concentration gradients in polymer electrolytes under DC polarization.
• To understand the dynamic structural evolution of these electrolytes at the nanoscale during operation.

Main Methods:

• Utilized in situ small-angle X-ray scattering (SAXS) for high-resolution spatial and temporal analysis.
• Examined a polystyrene-block-poly(ethylene oxide) copolymer electrolyte within a lithium symmetric cell under DC polarization.

Main Results:

• Observed a transition from lamellar morphology to disordered, lamellar, and gyroid phases under ionic current.
• Discovered the spontaneous growth of a current-induced gyroid phase for hours after field removal.
• Identified the formation of localized salt-dense "concentration hotspots" as the cause.

Conclusions:

• Nanostructure evolution under DC polarization significantly impacts electrolyte behavior.
• Concentration hotspots are a key phenomenon affecting electrolyte performance at high current densities.
• The developed in situ SAXS method provides a powerful tool for studying dynamic structures in composite electrolytes.