Tailoring the electronic structure to enable rapid Li-ion diffusion and a stabilized LiF–LiCl rich electrode–electrolyte interface

Abstract

The chemical composition of the solid electrolyte interphase (SEI) at the Li anode/electrolyte interface is critical to the performance of lithium metal batteries. Herein, we designed a functional ionic salt (DG-Cl) with a π-conjugated structure, aiming to enhance the electronic delocalization of the filler to regulate the bond-breaking kinetics and promote the formation of the effective components of the SEI. Density functional theory (DFT) verifies that DG-Cl is capable of releasing Cl⁻ directionally under an electric field and subsequently combining with Li⁺ to form LiCl. Simultaneously, DG-Cl can anchor TFSI⁻via cation vacancies. Besides, through its strong electron delocalization capability, DG-Cl could facilitate the cleavage of C–F bonds of TFSI⁻ during the binding process (with charge transfer reaching up to 1.8453e⁻), thereby promoting the formation of more LiF. XPS and TOF-SIMS confirmed the in situ uniform co-growth of LiF–LiCl on the SEI, which facilitates the Li-ion transport kinetics and regulates the lithium deposition behavior. Impressively, the lithium symmetric batteries deliver ultralong cycling stability over 4000 hours at 0.1 mA cm⁻² and over 2200 hours at 0.2 mA cm⁻² while the Li/LiFePO₄ full cells possess 82.04% capacity retention after 800 cycles at 2C. Besides, this approach to regulating electron transfer at the molecular level guarantees the outstanding cycling performance of pouch cells. After 150 cycles, the battery retention rate was 96.6%. This work proposes a new approach to achieving high-performance and stable lithium metal batteries (LMBs).