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

Abstract 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 (LiNi 0.8 Co 0.1 Mn 0.1 O 2 , 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.