However, these inorganic films are often thin, brittle, and vulnerable to cracking due to the volume effect of the Li anode during extended cycling[32]. Thus, a more flexible artificial SEI layers, such as polymer-lithium alloy hybrid artificial SEI layers[119, 120], has be developed. For example, Xie et al reported a poly(tetramethylene ether glycol) (PTMEG)-Li/Sn alloy hybrid layer on the Li metal surface[119]. The possible mechanism for forming the artificial SEI layer is shown in Figure 8a. Such a hybrid artificial layer not only provided a fast lithium-ion transport path on account of the Li/Sn alloy with ample Li vacancies, but also has a strong affinity for Li. Since PTMEG is similar to poly(ethylene oxide) (PEO) with a large number of C-O bonds. As a result, after only 20 cycles, many dendrites and dead Li were observed for the pristine Li, whereas the treated Li presents a smooth and compact deposition of Li+ as shown in Figure 8b and 8c.