Investigating Interfacial Chemistry for Pre-passivated Lithium-ion Battery Electrodes Employing Non-flammable Methyl(2,2,2-trifluoroethyl) Carbonate Electrolytes

Abstract

The transition to non-flammable electrolytes is essential to enhance the safety of rechargeable lithium-ion batteries in the context of rapid global electrification. However, these next-generation electrolytes often exhibit inferior electrochemical performance compared to conventional carbonate-based systems, hindering their practical application. Recent studies suggest that pre-passivating electrodes with conventional electrolytes can enhance performance for some next-generation electrolytes through interphase stabilization, yet a mechanistic understanding of this improvement remains to be established. In this work, we combine detailed electrochemical analysis with synchrotron-based hard X-ray photoelectron spectroscopy to investigate how pre-passivated electrodes influence the stability and performance of cells containing non-flammable electrolytes based on the solvent methyl(2,2,2-trifluoroethyl) carbonate (FEMC). We identify the anode solid electrolyte interphase (SEI) as the critical limiting factor towards use of FEMC electrolytes, with pre-passivation in conventional electrolytes significantly mitigating continuous electrolyte decomposition. Furthermore, our results show that the cathode electrolyte interphase (CEI) also plays a vital role, and that optimal performance is achieved by combining an SEI formed in a conventional electrolyte with a CEI formed in the FEMC electrolyte. These findings provide direct electrochemical and spectroscopic evidence for interphase-driven performance improvements, offering a practical pathway to advance non-flammable electrolyte technologies.