Molecular understanding of interphase formation via operando polymerization on lithium metal anode

The stable cycling of lithium electrode has been significantly impeded by the lack of comprehensive and in-depth understanding of the complicated chemistry and unclear formation/evolution mechanisms of solid-electrolyte interphase (SEI). Here we report the formation mechanism of an operando polymerized SEI at the Li/electrolyte interface in an ether electrolyte and its dynamic evolution during the lithium growth process. The polymerization process is initiated by the consumption of the polymerization inhibitor LiNO3 with the formation of inorganic lithium salts at the Li-electrolyte interface, followed by instantaneous ring-opening polymerization of the cyclic ether solvent triggered by the initiator FSO2NSO2· radical, leading to the formation of a polymeric-inorganic composite SEI. The resulted SEI exhibits excellent mechanical flexibility and self-healing property that can effectively accommodate more than 100 times’ swelling of lithium during growth by stretching and thinning itself from ∼100 nm to 7 nm, achieving an ultrahigh Coulombic efficiency (99.73%) for lithium plating/stripping.