Conjugation-mediated and polarity-switchable interfacial layers for fast cycling of lithium-metal batteries

Abstract

The solid electrolyte interphase (SEI) is a key property of lithium-metal batteries (LMBs), affecting their Coulombic efficiency, rate capability, and cycle life. However, conventional SEIs, primarily formed by the decomposition of lithium salts and fluorinated additives to create inorganic-dominant interphases, suffer from inhomogeneous Li deposition and low ionic conductivity. These intrinsic drawbacks accelerate severe side reactions with the electrolyte, cause rapid capacity fading and accumulation of dead Li, and present safety concerns, particularly under elevated current density. In this study, we unravel the essential role of the SEI on the Li-metal anode in LMBs by creating a conjugation-mediated and polarity-switchable interfacial architecture. The thiophene-embedded polymer-like SEI, formed by in situ electrochemical oligomerization of thiophene, enhances Li+ ion conductivity by coordinating with lone electron pairs in sp(2) orbitals. Concurrently, the conjugated pi systems involving sp(2) hybridized C=C bonds and S atoms enable switchable polarity of p(z) orbitals, facilitating dynamic electron-cloud redistribution during Li plating and stripping. This orbital-level adaptability accelerates Li+ migration, suppresses dendritic growth, and stabilizes the Li-metal surface under high-current operation. This study establishes a new paradigm in orbital-engineered interfacial design in LMBs, bridging molecular-scale electronic polarization with macroscopic fast-charging stability. Furthermore, our study underscores that fine-tuning the properties of the SEI and the cathode electrolyte interphase is key to unlocking the transformative potential of LMBs for practical applications.image