(296a) A Nanoscale Study of the Formation of the Solid Electrolyte Interphase in Li Ion Batteries

The Solid Electrolyte Interphase (SEI) is a passivating film formed on the surface of graphite anodes because of the reductive decomposition of electrolyte solvents during initial charging of a lithium ion battery (LIB). The SEI plays a crucial role on the cycling performance and storage life of LIB, protecting the electrolyte from complete decomposition but also providing additional resistance to Li ion transport. However, a comprehensive understanding of the structure and composition of the SEI is still lacking.

We have developed an in-house transmission electron microscope (TEM grid) embedded graphite/Li half cell, with a binder-free (BF) graphite anode prepared using electrophoretic deposition (EPD) of graphite nanoparticles. Using such a cell removes the ‘noise’ created by inactive components such as binders, and allows us to focus directly on the role of different electrolytes on the formation of the SEI and its relationship to the cell performance, and the growth of SEI at different voltages during initial charging. We were able to follow the growth of the SEI in-situ at the nanoscale. Coupled with X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Nuclear magnetic resonance (NMR), we have been able to identify the morphology and key chemical components of the SEI and how these vary with different electrolytes. Our results provide crucial insights into optimizing choices of electrolytes and anode materials for Li-ion batteries.