Bifunctional Electrolyte Additive Enabling Simultaneous Interphase Formation on Both Electrodes in High‐Energy Lithium‐Ion Batteries

Abstract The development of next‐generation Lithium‐ion batteries (LIBs) to meet the demands of advancing technology and energy storage requires focus on the formation of effective interphases on both the positive and negative electrodes. Different promising approaches to facilitate effective interphase formation are already known Out of these, the incorporation of film‐forming electrolyte additives is a straight‐forward strategy to achieve this goal. In the presented study, a bifunctional electrolyte additive, (5‐methyl‐2‐oxo‐1,3‐dioxol‐4‐yl)methyl thiophene‐3‐carboxylate composed of two functional motifs, vinylene carbonate (VC) and thiophene, is reported. Upon LIB operation, the additive undergoes in situ splitting, forming a VC‐assisted solid electrolyte interphase (SEI) and a polythiophene‐based cathode electrolyte interphase (CEI) simultaneously. The electrochemical performance of the proposed additive is studied in 250 mAh NMC811||AG + 20% SiO _x wound pouch cells, and shows considerable improvement in overall battery performance compared to cells with the baseline electrolyte. The additive's dual interphase formation is confirmed through a combination of advanced characterization techniques, including X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and operando shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS). This study introduces a new design strategy for a multifunctional electrolyte additive, providing a promising pathway to improve overall LIB's performance and lifetime by simultaneous stabilization of both electrodes through facilitated interphase formation.