Tailoring the Lithium Solid Electrolyte Interphase for Highly Concentrated Electrolytes with Direct Exposure to Halogenated Solvents

Abstract

We investigate the effect of pretreatment of Li metal electrodes with chloroethylene carbonate (CEC). In comparison with either untreated or fluoroethylene carbonate (FEC)-treated Li surfaces, the CEC-treated electrodes exhibit smaller overpotentials and greater stability in symmetric cell cycling using a highly concentrated acetonitrile-LiTFSI-based electrolyte. The origin of the more facile cycling behavior is associated with a thicker SEI originating from a condensation reaction of N- and O-containing reduction products. Full cells constructed using the CEC treatment exhibit cycling behaviors equivalent to those seen using the FEC treatment. Replacing the LiTFSI electrolyte with LiFSI diminishes the salubrious effect of surface treatment by either FEC or CEC due to consequences arising from the more complete decomposition of the FSI– anion upon Li metal exposure.

Synergy of an In Situ-Polymerized Electrolyte and a Li3N–LiF-Reinforced Interface Enables Long-Term Operation of Li-Metal Batteries

“…The weak LiF and Li 3 N peak should be generated from the decomposition of LiTFSI, and the lithium carbonates are induced by the reduction of organic solvents. The peak of Li 3 N appears stronger on the Li surface with LiNO 3 –GPE because of the reduced LiNO 3 , which readily participates in the formation of the SEI. , The enhanced signal of LiF indicates that LiNO 3 may accelerate the decomposition of LiTFSI, as has been confirmed by Zhang et al The peak intensity of LiF becomes stronger for Li with FEC/LiNO 3 –GPE, suggesting that the reduction of FEC plays a role to produce LiF. − In terms of the N 1s spectra (Figure d), the weak signals of Li 3 N (398.8 eV) and −NSO 2 CF 3 (398.8 eV) from the reduction of LiTFSI can still be seen with base liquid electrolyte. For the GPEs consisting of LiNO 3 , besides the strong signals of −NSO 2 CF 3 and Li 3 N, the two peaks at 403.2 and 408.1 eV are attributed to LiN x O y .…”

Forming Robust and Highly Li‐Ion Conductive Interfaces in High‐Performance Lithium Metal Batteries Using Chloroethylene Carbonate Additive

“…The Cl 2p XPS profiles (Figure 1e,f ) revealed the appearance of a 2p 3/2 peak of LiCl at the binding energy of 198.5 eV in the case of the ClEC electrolyte. [26] Figure S2, Supporting Information, demonstrates the presence of LiF in both the baseline electrolytes with and without ClEC, which is a feature of EF31D as a baseline electrolyte. [19] To evaluate the cycling stability of Li metal in the cell with the ClEC electrolyte, a Li||Li symmetric cell was galvanostatically cycled at a current density of 2.0 mA cm À2 for 2 h (4 mAh cm À2 ) (Figure 2a).…”

“…The Cl 2 p XPS profiles (Figure 1e,f) revealed the appearance of a 2 p 3/2 peak of LiCl at the binding energy of 198.5 eV in the case of the ClEC electrolyte. [ 26 ] Figure S2, Supporting Information, demonstrates the presence of LiF in both the baseline electrolytes with and without ClEC, which is a feature of EF31D as a baseline electrolyte. [ 19 ]…”

“…[19] ClEC is a form of FEC in which F is substituted with Cl, and it forms Cl compounds in both the anode and cathode via the same mechanism as the formation of LiF from FEC. [24][25][26] LiCl, which has Li-ion diffusion barrier that is half as low as that of LiF but is still sufficiently robust, [27][28][29] facilitates Li-ion transport in the SEI and cathode-electrolyte interphase (CEI) layers. ClEC initially attracted attention as a solvent for SEI layer formation in early LIB research, along with FEC.…”