Lithium metal has been regarded as the most promising anode material for future high energy density lithium ion battery due to its high theoretical capacity (~3860mAh/g) and the lowest electrochemical potential (-3.04V vs the standard hydrogen electrode). The limitations for lithium metal to be the ideal anode are mainly the uncontrollable dendritic lithium growth and low coulombic efficiency. This work uses the lab-made fresh thin lithium foil with the thickness of 50 µm to eliminate the thickness influence on cycle life. The following research mainly focus on understanding the failure mechanism of lithium metal anode from aspect of salt and solvent in electrolyte. Two and three electrode symmetric lithium metal coin cells were made using different electrolyte (lithium hexafluorophosphate –LiPF₆, Lithium bis(trifluoromethanesulfonyl)imide –LiTFSI and Lithium bis(trifluoromethanesulfonyl)imide – LiFSI in Ethylene Carbonate and Diethyl Carbonate with volume ratio 50:50) with different concentration to test long cycle stability. The cycle life data shows the decreasing cycle life with the increasing mole concentration of LiFSI and LiTFSI electrolyte, while the cycle life of the cells using LiPF₆ electrolyte increases when using higher concentration. We believe both solvent and salt decomposition reactions influence the composition of Solid Electrolyte Interphase – SEI on lithium metal when cycling. Fourier-transform infrared spectroscopy (FTIR) and Nuclear magnetic resonance (NMR) will be used to realize the decomposition product of solvent and X-ray photoelectron spectroscopy (XPS) will be used to figure out the salt decomposition product. The evidence of lithium dendrite pierce the separator has been found by using Focused Ion Beam (FIB) with Scanning Electron Microscopy (SEM). Also the thickness of dead lithium will growth with cycles to fulfill the available space in the cells. Both coin cells and Electrochemical Quartz Crystal Microbalance (EQCM) were made to calculate the columbic efficiency by using different electrolyte mentioned above. Electrochemical impedance spectroscopy (EIS) was used to analysis the SEI and charge transfer resistance change during cycles to identify which part mostly contribute the overpotential. In this work, we will figure out the decomposition reactions of solvent and salts to analysis the failure mechanism.