Anion-Reinforced Solvating Ionic Liquid Electrolytes Enabling Stable High-Nickel Cathode in Lithium-Metal Batteries

Ionic liquid electrolytes (ILEs) are promising to develop high-safety and high-energy-density lithium-metal batteries (LMBs). Unfortunately, ILEs normally face the challenge of sluggish Li+ transport due to increased ions' clustering caused by Coulombic interactions. Here a type of anion-reinforced solvating ILEs (ASILEs) is discovered, which reduce ions' clustering by enhancing the anion-cation coordination and promoting more anions to enter the internal solvation sheath of Li+ to address this concern. The designed ASILEs, incorporating chlorinated hydrocarbons and two anions, bis(fluorosulfonyl) imide (FSI-) and bis(trifluoromethanesulfonyl) imide (TFSI-), aim to enhance Li+ transport ability, stabilize the interface of the high-nickel cathode material (LiNi0.8Co0.1Mn0.1O2, NCM811), and retain fire-retardant properties. With these ASILEs, the Li/NCM811 cell exhibits high initial specific capacity (203 mAh g-1 at 0.1 C), outstanding capacity retention (81.6% over 500 cycles at 1.0 C), and excellent average Coulombic efficiency (99.9% over 500 cycles at 1.0 C). Furthermore, an Ah-level Li/NCM811 pouch cell achieves a notable energy density of 386 Wh kg-1, indicating the practical feasibility of this electrolyte. This research offers a practical solution and fundamental guidance for the rational design of advanced ILEs, enabling the development of high-safety and high-energy-density LMBs. An anion-reinforced solvating ionic liquid electrolyte is developed to enhance the anion-cation coordination and promote more anions to enter the internal solvation sheath of Li+. This new type of ionic liquid electrolyte improves Li+ transport ability and stabilizes the interface between the electrolyte and high-nickel cathode, rendering the practical application toward high-safety and high-energy-density lithium-metal batteries. image