Lithium-7 NMR spectroscopy was employed to search for the methods to prevent the formation of dendrites in a lithium metal battery (LMB). Electrode-protecting polymer films including Li7La3Zr2O12 was effective while Li-Ag (95:5 wt%) alloy was not. In the meanwhile, the dynamics of Li ions in LMB constituents such as electrolytes, electrode-protecting polymer, and solid electrolyte interface (SEI) was investigated: in the presence of liquid electrolyte, Li ions were most mobile in electrolyte, next in electrode-protecting polymer, and least in SEI. In addition, the Li ions between and outside of Li metal double layers were differentiated.