Triazine‐Anion‐Based Fluorine‐Free Ionic Liquids and Lithium Battery Electrolytes With Flexible Cations

Herein, we introduce fluorine‐free ionic liquids (ILs) and electrolytes based on electron‐deficient triazine, 4,6‐Diethoxy‐2‐Oxo‐2H‐1,3,5‐Triazin‐5‐ide, (DET), ‐anion coupled with oligoether‐functionalized pyrrolidinium and imidazolium cations. Having the same anion, imidazolium IL show slightly better thermal and electrochemical stabilities, but lower ion transport and higher glass transition temperature, T _g , compared to its pyrrolidinium analog. Doping neat ILs with 20% lithium DET salt and creating lithium‐conducting electrolytes increases the overall thermal and electrochemical stabilities but decreases the ion mobilities. As the lithium battery electrolyte, Li∥Li symmetric cells confirm stable and reversible Li cycling for both electrolytes, with the imidazolium system showing lower polarization and midpoint hysteresis, indicating faster interfacial kinetics and reduced resistance; correspondingly, it also delivers narrower charge–discharge plateaus and improved voltage stability in Li∥LFP half‐cells. For imidazolinium‐based electrolytes, with the addition of 5 wt% vinylene carbonate (VC), the Li∥LFP cells exhibited excellent rate capability from 0.1C to 1C at 60 °C and maintained stable cycling around 200 cycles at 0.1C with nearly 99% capacity retention and coulombic efficiency, demonstrating enhanced interfacial stability and efficient lithium‐ion transport.