Study on an Interpenetrating Artificial SEI for Lithium Metal Anode Modification and Fast Charging Characterization

Artificial SEI is one of the effective strategies to improve lithium dendrites and suppress side reactions. However, the role of SEI components and distribution on the modification of the lithium metal anode remains unclear. Therefore, in this study, the oxygen-sulfur (O-S) component and its distribution in SEI were modulated by designing experiments, and then the mechanism of its action was deeply investigated. The study is based on an in-depth analysis of the properties of lithium sulfide (Li₂S) and lithium oxide (Li₂O) as SEI layer materials and effectively combines them in an ether electrolyte environment to form an innovative SEI structure. The experimental results show that the optimal SEI modulation condition is O120-S10. O120-S10 significantly improves the kinetic performance of electrochemical reactions, reduces the film resistance, and achieves cycling stability of up to 2100 h during high-capacity lithium deposition/stripping at 5 mAh cm^-2. When used in conjunction with a ternary cathode material (NCM811), the O120-S10 demonstrates excellent performance under high rate charge/discharge conditions at 10C. After 1500 cycle tests, the battery's specific capacity was maintained at 90 mAh g^-1 and the Coulombic efficiency reached 98.52%. Through X-ray photoelectron spectroscopy (XPS) analysis, the vertical structure and ratio distribution of components in SEI were revealed in detail, and the optimal component ratios of Li₂S 46.48%, Li₂O 46.02%, and Li₂CO₃ 7.50% were determined. The mechanism of action is to achieve a 1 + 1 > 2 superlinear synergistic effect and fast charging performance by combining the ability of Li₂O's low lithium ion diffusion barrier with Li₂S's ability to inhibit the growth of lithium dendrites.