Reinforcing The Electrode/Electrolyte Interphases of Lithium Metal Batteries Employing Locally Concentrated Ionic Liquid Electrolytes.

Lithium metal batteries (LMBs) with nickel-rich cathodes are promising candidates for next-generation high-energy-density batteries, but the lack of sufficiently protective electrode/electrolyte interphases (EEIs) limits their cyclability. Herein, trifluoromethoxybenzene is proposed as a co-solvent for locally concentrated ionic liquid electrolytes (LCILEs) to reinforce the EEIs. With a comparative study of a neat ionic liquid electrolyte (ILE) and three LCILEs employing fluorobenzene, trifluoromethylbenzene, or trifluoromethoxybenzene as co-solvents, it is revealed that the fluorinated groups tethered to the benzene ring of the co-solvents not only affect the electrolytes' ionic conductivity and fluidity, but also the EEIs' composition via adjusting the contribution of the 1-ethyl-3-methylimidazolium cation (Emim + ) and bis(fluorosulfonyl)imide anion. Trifluoromethoxybenzene, as the optimal co-solvent, leads to a stable cycling of LMBs employing 5 mAh cm -2 lithium metal anodes (LMAs), 21 mg cm -2 LiNi 0.8 Co 0.15 Al 0.05 (NCA) cathodes, and 4.2 μL mAh -1 electrolytes for 150 cycles with a remarkable capacity retention of 71%, thanks to a solid electrolyte interphase rich in inorganic species on LMAs and, particularly, a uniform cathode/electrolyte interphase rich in Emim + -derived species on NCA cathodes. In contrast, the capacity retention under the same condition is only 16%, 46%, and 18% for the neat ILE and the LCILEs based on fluorobenzene and benzotrifluoride, respectively. This article is protected by copyright. All rights reserved.