High-Polarity Fluoroalkyl Ether Electrolyte Enables Solvation-Free Li + Transfer for High-Rate Lithium Metal Batteries.

Lithium metal batteries (LMBs) have aroused extensive interest in the field of energy storage owing to the ultrahigh anode capacity. However, strong solvation of Li + and slow interfacial ion transfer associated with conventional electrolytes limit their long-cycle and high-rate capabilities. Herein an electrolyte system based on fluoroalkyl ether 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether (THE) and ether electrolytes is designed to effectively upgrade the long-cycle and high-rate performances of LMBs. THE owns large adsorption energy with ether-based solvents, thus reducing Li + interaction and solvation in ether electrolytes. With THE rich in fluoroalkyl groups adjacent to oxygen atoms, the electrolyte owns ultrahigh polarity, enabling solvation-free Li + transfer with a substantially decreased energy barrier and ten times enhancement in Li + transference at the electrolyte/anode interface. In addition, the uniform adsorption of fluorine-rich THE on the anode and subsequent LiF formation suppress dendrite formation and stabilize the solid electrolyte interphase layer. With the electrolyte, the lithium metal battery with a LiFePO 4 cathode delivers unprecedented cyclic performances with only 0.0012% capacity loss per cycle over 5000 cycles at 10 C. Such enhancement is consistently observed for LMBs with other mainstream electrodes including LiCoO 2 and LiNi 0.5 Mn 0.3 Co 0.2 O 2 , suggesting the generality of the electrolyte design for battery applications.