PNNL

Abstract

The lifespan of lithium (Li) metal batteries (LMBs) can be greatly improved by the generation of inorganic-rich electrode-electrolyte interphases (EEIs). In this work, a fluorinated ether with weakly-solvating ability, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (BTFEE), was used as a diluent as well as a co-solvent in the localized high-concentration electrolyte (LHCE) system containing LiFSI salt and 1,2-dimethoxyethane (DME) solvent. Unlike other reported inert diluents, BTFEE not only acts as a diluent for the salt-solvent clusters, but also enhances anion decomposition kinetics at electrode surfaces and promotes the formation of more inorganic-rich EEI layers (including solid-electrolyte interphase on anode and cathode-electrolyte interphase on cathode), and meanwhile partially decomposes and forms part of EEI layers. With an optimized molar ratio of LiFSI:DME:BTFEE = 1:1.15:3, LMBs with a lithium nickel manganese cobalt oxide (LiNi0.8 Mn0.1 Co0.1) cathode at 4 mAh cm-2 loading can retain 80% capacity in 470 cycles in the voltage range of 2.8-4.4 V. The fundamental understanding on the functionality of BTFEE revealed in this work provides new perspectives on the design of practical high-energy density battery systems.