Upgrading interface chemistry via high dielectric constant and enhanced electronic localization COF for lithium metal batteries

To advance the development of high-performance lithium metal batteries (LMBs), precisely regulating the chemical composition of the solid electrolyte interphase (SEI) is essential, especially by increasing the LiF concentration. Currently, the primary approaches for constructing LiF-rich SEI layers rely predominantly on the decomposition of lithium salts. However, most studies have yet to thoroughly investigate the influence of charge density and anion concentration on the decomposition mechanism of lithium salts. Herein, we design covalent organic frameworks (COFs) with high dielectric constants and enhanced electronic localization to increase the dissociation degree of the lithium salt and facilitate rapid charge transfer, with the aim of promoting the efficient decomposition of anions to construct a stable LiF-rich SEI. In situ analytical tools and theoretical calculations reveal that 2CN-COF induces the formation of a LiF-rich SEI for interfacial optimization, while the one-dimensional pore channels of cyano-functionalized COFs serve as rapid and directional ion transport pathways to generate a uniform lithium-ion flux. Benefiting from this strategy, a battery assembled with a 50 μm ultrathin lithium anode and a LiFePO 4 cathode demonstrates outstanding electrochemical performance, maintaining 88% capacity retention after 700 cycles. The anion decomposition strategy proposed in this study opens new avenues for the practical application of LMBs.