Surface Reconstruction Limited Conductivity in Block-Copolymer Li Battery Electrolytes

TL;DR

This paper investigates how surface modifications of electrodes with PEO brushes improve the conductivity and reproducibility of block-copolymer electrolytes in lithium batteries, highlighting the importance of nanoscale surface composition.

Contribution

It demonstrates that PEO-brush surface modification stabilizes impedance measurements and enhances electrolyte performance, addressing surface reconstruction effects in polymer electrolytes.

Findings

PEO-brush coating increases electrolyte conductivity.

Surface reconstruction affects impedance measurements.

Surface modification leads to more reproducible results.

Abstract

Solid polymer electrolytes for lithium batteries promise improvements in safety and energy density if their conductivity can be increased. Nanostructured block copolymer electrolytes specifically have the potential to provide both good ionic conductivity and good mechanical properties. This study shows that the previously neglected nanoscale composition of the polymer electrolyte close to the electrode surface has an important effect on impedance measurements, despite its negligible extent compared to the bulk electrolyte. Using standard stainless steel blocking electrodes, the impedance of lithium salt-doped poly(isoprene-b-styrene-b-ethylene oxide) (ISO) exhibited a marked decrease upon thermal processing of the electrolyte. In contrast, covering the electrode surface with a low molecular weight poly(ethylene oxide) (PEO) brush resulted in higher and more reproducible conductivity values, which were insensitive to the thermal history of the device. A qualitative model of this effect is based on the hypothesis that ISO surface reconstruction at the different electrode surfaces leads to a change in the electrostatic double layer, affecting electrochemical impedance spectroscopy measurements. As a main result, PEO-brush modification of electrode surfaces is beneficial for the robust electrolyte performance of PEO-containing block-copolymers and may be crucial for their accurate characterization and use in Li-ion batteries.