Three-dimensional electronic resistivity mapping of solid electrolyte interphase and anode active material in lithium-ion batteries

Abstract

Silicon is a promising candidate for the lithium ion battery anode because of the order-of-magnitude improvement in gravimetric energy density over current state-of-the-art graphite anodes. In systems featuring both C and Si anodes, electronic resistivity of the solid-electrolyte interphase (SEI) layer is a critical factor for preventing continuous electrolyte decomposition reactions at the electrode/electrolyte interface. Moreover, the degradation of electronic conductivity of Si active material through electrochemical cycling is believed to be partially responsible for capacity fade in the Si-based anode. However, the in-situ measurement of electronic resistivity of SEI and Si active material has been complicated by ion transport and electronic contributions from other parts of the battery circuit. Ex-situ measurements of resistivity at nanometer scales are also lacking. This research seeks to further the understanding of the electronic and structural properties of the SEI and Si active material at the nanoscale through development of a novel experimental approach. The method described in this work employs scanning spreading resistance microscopy (SSRM) on SEI formed on crystalline Si to map electronic resistivity in three dimensions with high resolution. Results obtained with this technique are compared to results on the same samples through scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), and secondary ion mass spectroscopy (SIMS). This thesis aims to develop the understanding of the electronic properties of SEI and their influence on battery performance and to establish protocols for the collection, analysis, and verification of novel SSRM-based characterization of material interfaces in two-dimensional and three-dimensional lithium-ion battery electrodes.