Understanding the formation chemistry of native solid electrolyte interphase over lithium anode and its implications using a LiTFSI/TME-TTE electrolyte and polysulfide additive

To develop high energy density Li batteries, Li metal anodes and in situ plated Li anodes (i.e., the so-called anode-free approach) have been extensively studied. However, the high reactivity of the Li metal surface can lead to chemical reactions with electrolyte components upon contact. Consequently, the so-called native solid electrolyte interphase (SEI) species are formed spontaneously when the Li anode is in contact with the electrolyte. This study illustrates the formation chemistry of native SEI over a Li metal surface using lithium bis(trifluoromethanesulfonyl)imide in tetramethylene sulfone and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (LiTFSI/TMS-TTE) electrolyte with and without lithium polysulfide (PS) additive. All electrolyte components were found to decompose over the Li surface based on diffuse reflectance infrared Fourier-transformed spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and ab initio molecular dynamics (AIMD) simulation. The degradation mechanism and the evolved SEI species of each electrolyte component were carefully evaluated. The PS additive can significantly influence the composition of native SEI via its decomposition prior to all other electrolyte components, which can consequently suppress the degradation of the other electrolyte components, namely, TTE, TMS, and LiTFSI. The results indicate the importance of proper selection of electrolyte components, which can lead to the possibility of tuning such native SEI species to stabilize the Li surface in subsequent electrochemical cycling.