Revisiting Carbonate Additives through Dynamic Regulationof Cathode Electric Double Layers

Abstract Carbonate additives such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are widely used to stabilize high-voltage lithium metal batteries (LMBs), but their roles are generally interpreted through a static film-forming mechanism. Here, we reassess their functions at LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes up to 4.6 V using in-situ electrochemical surface-enhanced Raman spectroscopy (EC-SERS), theoretical calculations, and systematic electrochemical evaluation. VC and FEC not only contribute to cathode electrolyte interphase formation but also dynamically regulate the cathode-side electric double layer (EDL). By reducing its potential sensitivity, they suppress potential-driven redistribution and excessive enrichment of carbonate solvents and PF6– near the highly oxidizing NCM811 surface, thereby limiting continuous electrolyte decomposition. Compared with VC, FEC provides more durable protection by forming a LiF-rich organic–inorganic hybrid interphase. These findings reveal a new EDL-regulation mechanism for conventional carbonate additives and are expected to provide guidance for electrolyte design in high-voltage LMBs.