The theoretical specific capacity of metal lithium reaches 3860mAh/g, the potential is only -3.04V (vs standard hydrogen electrode), and it has excellent electronic conductivity. It is an ideal lithium ion battery negative electrode material. However, the presence of local polarization in the repeated charge and discharge process of lithium metal anodes causes dendrite growth and electrode powdering problems, which limits the large-scale application of lithium metal anodes. LiNO3 is effective in improving the stability of the metal lithium interface. Additives, but the mechanism of its action in the electrolyte is still unclear. The composition of the SEI film can be changed by adjusting the electrolyte composition, which has a significant impact on the deposition behavior of lithium metal. Therefore, the author here studied the influence of the electrolyte composition on the structure of the SEI film by adjusting the ratio of LiNO3 and LiTFSI. It is found that in the presence of LiNO3, the composition of the SEI film is more complex, thicker, and denser. At the same time, the decomposition product of LiNO3, LixNyOz, significantly improves the ion conduction efficiency of the SEI film and the stability of the SEI film. The deposition morphology of metallic lithium is smoother and more uniform. In order to analyze the exchange reaction rate of Li in different SEI membranes under actual working conditions, the author conducted a test in the presence of electrolyte. Since the electrolyte can penetrate into the pores of the SEI membrane, the exchange reaction becomes more complicated. There is a three-phase reaction of electroly