Surface Sensitive NMR Detection of the SEI Layer on Reduced Graphene Oxide

TL;DR

This paper introduces a novel application of dynamic nuclear polarization (DNP) to enhance solid state NMR sensitivity for studying the solid electrolyte interphase (SEI) on reduced graphene oxide in batteries, enabling detailed molecular insights.

Contribution

First use of DNP-enhanced ssNMR to detect and differentiate SEI layers on rGO, improving sensitivity for battery interface analysis.

Findings

DNP enhances outer SEI layer signals at natural abundance 13C.

Enriched electrolyte measurements at 100K differentiate inner and outer SEI.

Method enables molecular-level understanding of SEI composition.

Abstract

The solid electrolyte interphase (SEI) is detrimental for rechargeable batteries performance and lifetime. Understanding its formation requires analytical techniques that provide molecular level insight. Here dynamic nuclear polarization (DNP) is utilized for the first time for enhancing the sensitivity of solid state NMR (ssNMR) spectroscopy to the SEI. The approach is demonstrated on reduced-graphene oxide (rGO) cycled in Li-ion cells in natural abundance and 13C-enriched electrolyte solvents. Our results indicate that DNP enhances the signal of outer SEI layers, enabling detection of natural abundance 13C spectra from this component of the SEI at reasonable timeframes. Furthermore, 13C- enriched electrolytes measurements at 100K provide ample sensitivity without DNP due to the vast amount of SEI filling the rGO pores, thereby allowing differentiating the inner and outer SEI layers composition. Developing this approach further will benefit the study of many electrode materials, equipping ssNMR with the needed sensitivity to efficiently probe the SEI.