Li metal batteries (such as lithium - sulfur (Li - S) and lithium-air batteries) have been strongly considered as the promising candidates for the next-generation energy storage devices. Unfortunately, as the result of the notorious Li dendrite growth inherent in these batteries (upon repeated charge/discharge cycling), the concomitant serious safety concerns and low Coulombic efficiency have retarded their practical applications. Herein, we report a facile but effective strategy to in-situ construct a stable and compact solid electrolyte interphase (SEI) layer to protect Li deposits by the synergetic effect of Li_2S_5-based ternary-salt (LiTFSI-LiNO_3-Li_2S_5) electrolyte. LiTFSI affords a high Li conductivity of the electrolyte in a working battery. The reactions between LiNO_3 and Li_2S_5 induce Li_2SO_3 formation, which is favorable to build protective SEI layer. Compared with routine LiTFSI mono-salt electrolyte, the Li_2S_5-based ternary-salt electrolyte renders Li metal anode (1) dendrite-free morphology, (2) improved Coulombic efficiency (94% compared with 60% in routine electrolyte), (3) suppressed polarization, and (4) prolonged lifespan (80 h compared with 20 h). These superior characteristics are attributed to the enhanced stability of the SEI layer by deliberately introducing the Li_2S_5 polysulfide as a pre-existing precursor, which, however, is always considered as an undesirable intermediate in Li-S batteries. Further development of this electrolyte enables practical applications for rechargeable lithium metal batteries, especially Li-S batteries.
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