Electrochemical behaviors of a Li3N modified Li metal electrode in secondary lithium batteries

Abstract

A lithium conductive Li3N film is successfully prepared on Li metal surface by the direct reaction between Li and N2 gas at room temperature. X-ray diffraction (XRD), Auger electron spectroscopy (AES), cyclic voltammetry (CV), scanning electron microscopy (SEM), AC impedance, cathodic polarization and galvanostatic charge/discharge cycling tests are applied to characterize the film. The experimental results show that the Li3N protective film is tight and dense with high stability in the electrolyte. Its thickness is more than 159.4nm and much bigger than that of a native SEI film formed on the lithium surface as received. An exchange current as low as 3.244×10−7A demonstrates the formation of a complete SEI film at the electrode|electrolyte interface with Li3N modification. The SEI film is very effective in preventing the corrosion of the Li electrode in liquid electrolyte, leading to a decreased Li|electrolyte interface resistance and an average short distance of 3.16×10−3cm for Li ion diffusion from electrolyte to Li surface. The Li cycling efficiency depends on N2 exposing time and is obviously enhanced by the Li3N (1h) modification. After cycling, a dense and homogeneous Li layer deposits on the Li3N (1h) modified Li surface, instead of a loose and inhomogeneous layer on the Li surface as received.