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 (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.