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

Rechargeable lithium metal (Li⁰) 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 (Al⁰) 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 Al⁰ current collector at high potentials (>4.2 V versus Li/Li⁺) and significantly improves the cycling performance of Li(Ni_1/3Mn_1/3Co_1/3)O₂ (NMC111) cells. In addition, this sulfonimide salt results in the growth of an advantageous solid electrolyte interphase on the Li⁰ electrode. The replacement of either LiTFSI or LiPF₆ with LiDFTFSI endows a Li⁰||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.