Generation of a highly conductive and stable solid electrolyte interphase at lithium anode under additional electric filed

• A solution to optimize SEI layer was developed by applying electric field. • The electric field promotes the anions to the surface of lithium anode. • The anions participate in the formation of SEI layer. • The SEI layer has fast diffusion channels for lithium ions. • Batteries with this layer exhibit good cycling performance. The solid electrolyte interphase (SEI) generated spontaneously on the surface of lithium anode, is a protective layer to inhibit further reaction of electrolyte with lithium and to prevent the formation of lithium dendrites. The composition and properties of SEI layers determine the cycling performance of lithium batteries to some extent. Here we report a novel solution to optimize the SEI layer by applying an additional alternating current (AC) electric field during the generation of SEI. The application of an AC field enhances the association of anions and cations in the electrolytes, which results in an improved delivery of anions to the surface of lithium anode. The decomposition of anions at the surface leads to the formation of an anion-derived SEI layer containing a mass of LiF and Li 2 S particles. The grain boundaries among these particles provide fast diffusion channels for lithium ions, forming a high conductive SEI layer. The optimized composition of SEI layer is confirmed by X-ray photoelectron spectroscopy analysis and electrochemical characterizations. Through this strategy, the cycle performance of lithium batteries is greatly improved, and the stable cycling life of Cu@Li | Li cells and Cu@Li | NMC811 cells increases more than 3 times.