Multifunctionalizing electrolytes in situ for lithium metal batteries

Lithium metal batteries (LMBs) are next-generation high-energy rechargeable batteries, in which an ideal multifunctional electrolyte additive has been desired to simultaneously stabilize the electrolyte salt, scavenge the electrolyte detrimental impurities, and protect both the lithium anode and cathode. Here, we report a new concept of introducing Lewis acid-base coordinations into electrolytes to synthesize Lewis acid-base complexes in situ as multifunctional electrolyte additives for LMBs. For proof of concept, by introducing fluoroethylene carbonate (FEC) as the Lewis acid and tris(trimethylsilyl) phosphite (TMSP) as the Lewis base into a conventional carbonate electrolyte, an acid-base complex (TMSP: FEC) is formed in situ to act as an electrochemically-clean environment for cleaning and stabilizing the electrolyte while reinforcing the electrode surface coatings with multi-components from the complex. The preferential reduction and oxidation of the complex derive mechanically strong and lithium-ion conductive surface coatings to protect the lithium anode and cathode, respectively. Synergistically, these multifunctionalities of the complex ensure an extraordinary Li platting/stripping with an extremely low polarization overpotential of 11 mV for over 16,000 h, and thereby enable high-performance LMBs based on a high-potential LiNi0.5Mn1.5O4, high-capacity LiNi0.8Mn0.1Co0.1O2, or high-safety LiFePO4 cathode with a high packing and high areal capacity. This work opens up a new avenue for in-situ multifunctionalizing electrolytes for LMBs and beyond.