Revisiting Carbonate Additives through Dynamic Regulation of Cathode Electric Double Layers.

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.