Figure 8 (a) Possible reaction mechanism for the formation of the PTMEG-Li/Sn alloy hybrid layer. SEM images of Li-Li symmetric cells with (b) the pristine Li and (c) SnCl4+THF treated Li after 20 cycles at 1 mA·cm−2, 1 mA·h·cm−2. All scale bars are 20 μm. (Reproduced from ref.[119], with permission from Copyright © 2019 Wiley-VCH.)
Moreover, researchers have also developed various kinds of lithium-containing alloys artificial protective layers. The protective lithium alloy layers are generally thin films formed on the Li metal surface via chemical/electrochemical pre-treatment[85, 109-120], mechanical press[121, 122], magnetron sputtering[60], etc., which are acceptable ionic conductivity for Li migration as well as suppress the dendrite growth via homogenous deposition of lithium[32]. For example, Li group reported a magnetron sputtering method to deposit a thin Al film on lithium surface[60]. After depositing, the Li-Al alloy layer would be formed on the lithium metal surface and guide dense Li deposition. Mai’s group reported an artificial Li-Al interphase layer on Li-B alloy anode[121, 122]. The Li-Al layer form in situ on the Li-B electrode via pressing Al foil with Li-B foil discs under a pressure of 120 Mpa, then kept at this pressure for several minutes or lithiated after 10 min. The artificial Li-Al layer allowed electron and ion transport to Li-B electrode. The Li-Al layer coating on Li-B electrode can improve cyclic life over 1200 h at a current density of 0.2 mA·cm−2, whereas bare Li-B electrode has stable cycles not exceeding 800 h. In addition, when it assembled with LiMn0.8Fe0.2PO4 cathode and Li1.5Al0.5Ge1.5(PO4)3electrolyte, the resulted solid state batteries could deliver an initial discharge capacity of 153 mA·h·g−1 with good cyclic stability and rate performance at 50 °C.