Impact of the Si Electrode Morphology and of the Added Li-Salt on the SEI Formed Using EMIFSI-Based Ionic-Liquid Electrolytes

This work presents an in-depth chemical and morphological investigation of the solid electrolyte interphase (SEI) formed on binder-free silicon electrodes, which include both nanowire (Si-NW) and amorphous (a-Si) configurations, for next-generation lithium-ion battery systems. The study focuses on the first five galvanostatic cycles to capture the critical early-stage SEI consolidation process, essential for understanding the interfacial phenomena that dictate long-term performance. By employing innovative electrode fabrication techniques such as plasma-enhanced chemical vapor deposition and utilizing ionic liquid (IL)-based electrolytes—specifically 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI) formulations known for their low viscosity and high conductivity—this work addresses the challenges posed by the significant volume changes inherent to Si-based materials. Advanced characterization methodologies, notably Optical-Photothermal Infrared Spectroscopy (O-PTIR) and Raman spectroscopy are utilized to probe the chemical and structural evolution of the SEI with high spatial resolution. This multifaceted approach reveals the interplay between electrode morphology and electrolyte composition on SEI formation and provides valuable insights into the fundamental processes governing irreversible capacity losses and electrode degradation. The findings demonstrate clear material- and electrolyte-dependent differences in SEI characteristics, thereby establishing new avenues for optimizing interfacial stability and battery performance. Overall, the study contributes innovative perspectives on early SEI formation mechanisms critical for the design of safer and more durable high-capacity battery electrodes.