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.