Sifting weakly-coordinated solvents within solvation sheath through an electrolyte filter for high-voltage lithium-metal batteries

The compulsive lithium dendrite growth and inevitable electrolyte decomposition induced by immediate contact between electrodes and free/weakly coordinated solvent molecules within the solvation sheaths of solvated lithium-ions are long-lasting tricky problems that existed in lithium-metal batteries (LMBs). Salt-concentrated strategy can effectively suppress those detrimental issues, the apparently increased production costs, the increased electrolyte viscosities, or even catastrophic battery explosions caused by adding extra salts, however, greatly restrained their successes. Here, by employing a metal-organic framework (MOF) with narrow channel sizes of 4.2 Å (ZIF-71) as a unique electrolyte solvation sheath filter to isolate free or weakly-coordinated solvents from contact with electrodes, we have obtained a special electrolyte composed of merely strongly coordinated solvent molecules. Drawn from the quantitative spectral analysis (FT-IR, Raman), the number of electrolyte solvent molecules in each Li+ solvation sheath was calculated to be 0.54 (the lowest value achieved among carbonate electrolytes), indicated almost completely de-solvation towards the solvated lithium-ions. This ZIF-71 filtered electrolyte displayed remarkably expanded electrochemical stability windows (extended to 5.2 V vs. Li/Li⁺). When coupled it with two typical high-voltage cathodes (4.4 V-level NCM-811 and 4.9 V-level LNMO), the high-voltage lithium-metal batteries demonstrated remarkably improved electrochemical performances in terms of capacities and lifespans. The cycled high-voltage cathodes and lithium metals demonstrate greatly improved electrode/electrolyte interfaces with negligible cathode electrolyte interface (CEI) and solid electrolyte interface (SEI). This special electrolyte filtering strategy is expected to push the development of high-energy-density LMBs.