Stable non-corrosive sulfonimide salt for 4-V-class lithium metal batteries.

Rechargeable lithium metal (Li) batteries (RLMBs) are considered attractive for improving Li-ion batteries. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) has been extensively used as a conducting salt for RLMBs due to its advantageous stability and innocuity. However, LiTFSI-based electrolytes are corrosive towards aluminium (Al) current collectors at low potentials (>3.8 V versus Li/Li), thereby excluding their application in 4-V-class RLMBs. Herein, we report on a non-corrosive sulfonimide salt, lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide (LiDFTFSI), that remarkably suppresses the anodic dissolution of the Al current collector at high potentials (>4.2 V versus Li/Li) and significantly improves the cycling performance of Li(NiMnCo)O (NMC111) cells. In addition, this sulfonimide salt results in the growth of an advantageous solid electrolyte interphase on the Li electrode. The replacement of either LiTFSI or LiPF with LiDFTFSI endows a Li||NMC111 cell with superior cycling stability and capacity retention (87% at cycle 200), demonstrating the decisive role of the salt anion in dictating the electrochemical performance of RLMBs.