Fluoroethylene Carbonate Induces Ordered Electrolyte Interface on Silicon and Sapphire Surfaces as Revealed by Sum Frequency Generation Vibrational Spectroscopy and X-ray Reflectivity

Abstract

The cyclability of silicon anodes in lithium ion batteries (LIBs) is affected by the reduction of the electrolyte on the anode surface to produce a coating layer termed the solid electrolyte interphase (SEI). One of the key steps for a major improvement of LIBs is unraveling the SEI's structure-related diffusion properties as charge and discharge rates of LIBs are diffusion-limited. To this end, we have combined two surface sensitive techniques, sum frequency generation (SFG) vibrational spectroscopy, and X-ray reflectivity (XRR), to explore the first monolayer and to probe the first several layers of electrolyte, respectively, for solutions consisting of 1 M lithium perchlorate (LiClO) salt dissolved in ethylene carbonate (EC) or fluoroethylene carbonate (FEC) and their mixtures (EC/FEC 7:3 and 1:1 wt %) on silicon and sapphire surfaces. Our results suggest that the addition of FEC to EC solution causes the first monolayer to rearrange itself more perpendicular to the anode surface, while subsequent layers are less affected and tend to maintain their, on average, surface-parallel arrangements. This fundamental understanding of the near-surface orientation of the electrolyte molecules can aid operational strategies for designing high-performance LIBs.

Fluorine and Lithium: Ideal Partners for High‐Performance Rechargeable Battery Electrolytes

“…[68] However,this surface alignment effect is only observable close to the electrode surface,whereas the parallel surface alignment is maintained in the outer interface layers. [69] This effect is illustrated in Figure 6. Furthermore,FEC can be blended with an organic linear carbonate.H ereby,t he replacement of hydrogen by fluorine leads to an improvement in cycling stability [59a,70] because of suppressed electrolyte decomposition as well as adecrease in the cell resistance and the formation of an effective SEI.…”

Solid Electrolyte Interphase on Native Oxide-Terminated Silicon Anodes for Li-Ion Batteries

“…47 The Si 2p and O 1s spectra at OCV and 0.8 V show minimal changes, which suggests that the native oxide layer remains intact, consistent with our XRR results. The small amount of Li and F present at the surface at 0.8 V is attributed to residual electrolyte even after DMC washing 48 and the formation of organic SEI, as well as possibly small amounts of electrolyte decomposition. [49][50][51] 0.7 V. Reducing the potential from 0.8 to 0.7 V results in changes in all spectra.…”

Electrochemical Oxidation of 5‐Hydroxymethylfurfural on Nickel Nitride/Carbon Nanosheets: Reaction Pathway Determined by In Situ Sum Frequency Generation Vibrational Spectroscopy

“…[7] NiFe layered double hydroxide (NiFeL DH) is the best catalyst reported in the electrooxidation of HMF at present, achieving an ear-quantitative yield of FDCA and 99.4 %f aradaic ef-ficiencyofH MF conversion. [12] In contrast, hydrogen, which has ahigh energy density,is nonpoisonous,a nd is environmentally friendly,i sagreen energy carrier and ap romising renewable energy source. However,the relationship of the conversion intermediates with the potential of the HMF electrooxidation on the surface of these electrocatalysts has rarely been studied.…”

“…[11] Yonatan Horowitz et al used SFG to study the orientation of ethylene carbonate on the anode surface of lithium-ion batteries. [12] In contrast, hydrogen, which has ahigh energy density,is nonpoisonous,a nd is environmentally friendly,i sagreen energy carrier and ap romising renewable energy source. Electrochemical water splitting, which typically involves ah ydrogen evolution reaction (HER) at the cathode and an oxygen evolution reaction (OER) at the anode,isastandard method for producing H 2 because of the high purity and low cost.…”