  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.
