Evolution effect of -CF2- group amount in hydrofluoroether on the solvation structure and high voltage cycle performance of Ether-based localized High-concentration electrolytes

Abstract

The high reactivity of Li metal and the security issues of electrolytes impede the practicality of lithium-metal batteries (LMBs). Herein, we propose a new localized high-concentration electrolyte (LHCE) in which, for the first time, 2,2,3,3-tetrafluoropropyl difluoromethyl ether (TDE) is employed as diluent in ether-based LHCE enables flame-retarded, broad electrochemical stability window, dendrite-free Li depositing, high Li anode cycling Coulombic efficiency (CE, 99.2%), and significantly improves cycling performance of Li||NMC811 batteries. It enables Li||NMC811 with limited 50 µm thickness Li metal anode and high loading capacity NMC811 cathode (14.8 mg cm−2, 2.96 mAh cm−2) to achieve a stable cycle with an ultrahigh cut-off voltage of 4.6 V. Molecular Dynamics (MD) simulation further corroborates the addition of hydrofluoroether diluents caused countersolvent effect to reinforce the association between Li+ cations and FSI− anions. However, an excessive amount of -CF2- in the diluent backbone would decrease the solubility of Li-salt in solvent, which is detrimental to the stability of electrolyte.