Gradient design for constructing artificial SEI layer towards high-performace Lithium metal batteries

The construction of artificial interfacial layer on Li anode is one of the most effective methods to block Li dendrite growth and volume expansion. The charge transport and ion diffusion behavior can be regulated due to the variation of component gradients and diffusion kinetics at different depths. However, there are few researches on the regulation of components’ distribution in artificial interfacial layer (SEI layer), which is of great significance for enhancing the electrochemical performance of Li anode. Herein, a gradient-design SEI layer is constructed on the Li anode to regulate charge transport and Li ion diffusion behavior in the interface, which could optimize the lithium deposition process. Based on this gradient structure, the gradient distribution of inorganic and organic components in the as-constructed SEI can effectively regulate the Li+ configuration and hinder the volume change during Li plating/stripping progress. With this hybrid interfacial layer, an improved cycling performance of Li-Li symmetric cell is achieved over 1750 h with a low overpotential under an ultrahigh current density of 10 mA cm−2, and ultrahigh capacity of 10 mAh cm−2. Based on the gradient-design artificial SEI film, the pouch cells matched with high-loading LiFePO4 cathode (21 mg cm−2) demonstrates extremely long cycling life with almost no capacity fade, which is superior compared with previous reports.