PNNL

Abstract

Lithium (Li) metal is considered as the ideal anode for high energy density rechargeable Li metal batteries (LMBs). However, the morphology instability of Li anode during electrochemical deposition/stripping leads to the uncontrolled growth of dendrites and the solid electrolyte interphase (SEI) layer which causes low Li Coulombic efficiency (CE) and rapid capacity fading in LMBs. Here, we report a carbonate-based localized high concentration electrolyte (LHCE) with a fluorinated ether as a diluent for 4-V class LMBs. This electrolyte consists of 1.2 M lithium bis(fluorosulfonyl)imide (LiFSI) in a co-solvent mixture of ethylene carbonate (EC)/ethyl methyl carbonate (EMC) with bis(2,2,2-trifluoroethyl) ether (BTFE) as diluent and 0.15 M lithium difluoro(oxalate)borate (LiDFOB) as additive. Using this electrolyte, dendrites-free Li deposition with a high Li CE (~98.5 %) is achieved. In addition, it offers much improved cycling stability of Li metal anode compared to previously reported dimethyl carbonate-based LHCEs. For example, a Li||NMC333 battery with a high areal loading of 3.8 mAh cm-2 maintains 84% of its initial capacity after 100 cycles. This is likely due to the highly robust SEI layer formed on the Li metal anode because of the decomposition of LiDFOB salt and EC solvent molecules. Therefore this novel electrolyte is promising for high energy density rechargeable LMBs.