Simultaneous construction of robust solid-electrolyte interphases by trifluoromethyl- and isocyanate-functionalized additives for sodium-ion batteries

Abstract

Electrolyte additives are essential for stabilizing interphases and improving the durability of sodium-ion batteries. In this study, 4-(trifluoromethyl)phenyl isocyanate (FMC) and 3,5-bis(trifluoromethyl)phenyl isocyanate (TFMC), which are functionalized with –CF₃ and NCO groups, are introduced as bifunctional additives that enable simultaneous film formation on both electrodes and scavenge HF through the isocyanate moiety. Notably, FMC exhibits adequate HF-scavenging ability, and TFMC facilitates the formation of C–F functionalized passivation layers on the surface of electrodes, which results in a significant enhancement of electrochemical performance. Specifically, TFMC, which is simultaneously functionalized with one NCO group and two CF₃ groups in the molecular structure, affords improved electrochemical performance, such as maintaining working voltage, retaining electrode morphology, and mitigating transition-metal dissolution. These results indicate that TFMC would be a promising additive for sodium-ion batteries based on task-specific molecular design.