Solubility-dependent protective effects of binary alloys for lithium anode

Recently, alloys have been widely utilized as protection layers for homogenize Li growth. However, the protective mechanisms for different alloys are not clearly understood. Herein, guided by the binary phase diagrams, Mg, Au, Zn, Al, Fe and Cu protective layers have been selected for study of their protective abilities and mechanisms. The selected metals can be classified into three categories according to the nature of their associated alloy protective layers: (1) Metals with high solubility in Li while not forming any intermediate line compounds, e.g. Mg, which is good for fast Li stripping. (2) Metals with limited solid solubility but forming stable line compounds with Li upon the lithiation, e.g. Au, Zn, and Al, where the formed stable line compounds LixAu, LixZn, LixAl will hamper Li kinetics. (3) Metals with negligible mutual solubility and no line compound formation with Li, e.g. Fe and Cu, which block Li stripping path and therefore result in highest polarization voltage.