Engineering Solid Electrolyte Interphase Composition by Assessing Decomposition Pathways of Fluorinated Organic Solvents in Lithium Metal Batteries

Abstract

Studies have shown fluorinated electrolyte solvents can form desirable solid electrolyte interphase (SEI) in lithium metal batteries. In this study, we develop a detailed mechanistic understanding of two high performing electrolytes, Fluoroethylene Carbonate (FEC) and Difluoroethylene Carbonate (DFEC) to demonstrate minimal structural variations can lead to different decomposition products, and thereby the nature of the SEI. Using density functional theory (DFT) calculations, we find different initial bond-breaking mechanisms between FEC and DFEC. We develop free energy diagrams for the decomposition pathways including both electrochemical and chemical steps. Using the computational Li electrode, we identify the largest limiting potential of 1.77 V for FEC decomposition, associated with the formation of lithium fluoride, lithium oxide and FEC oligomers, and 1.53 V for DFEC, which correspond to the formation of polymerized vinylene carbonate and lithium fluoride. We suggest the formation of oligomers in the case of FEC instead of long polymers may lead to better SEI compactness. We also demonstrate the SEI components of FEC and DFEC are not stable on typical cathode voltage (3.87 V). This study presents a unified electrocatalytic perspective on SEI formation and decomposition.

Recent Progress in the Development of Screening Methods to Identify Electrode Materials for the Oxygen Evolution Reaction

“…of catalysts in a homologous series of materials. Another promising starting point refers to the neighboring battery community, [116,117] which particularly applies high-throughput screening techniques for an assessment of solvent stabilities. [118,119] These methods and ideas could be of potential importance to the field of electrocatalysis in order to account for the stability aspect in trend studies (cf.…”

Leveraging Cation Identity to Engineer Solid Electrolyte Interphases for Rechargeable Lithium Metal Anodes

“…2,11,[18][19][20] Widely used strategies to control the composition and thickness of the SEI include tailoring the anion of the Li salt, 21 increasing the concentration of the electrolyte, [22][23][24][25][26] and using sacrificial organic electrolyte additives. [27][28][29] These strategies lead to increased amounts of LiF, cross-linking polymeric species, and polyene moieties in the SEI that are correlated with improved battery performance. 12,27,[30][31][32][33][34] Conversely, the ramifications of altering cation identity are more complicated, as the cation (e.g.…”

“…When examined with energy dispersive X-ray spectroscopy (EDS) and atomic absorption spectroscopy (AAS), we find that K + does not participate in electrochemical reaction. Rather, density functional theory (DFT) calculations, which are widely applied to study electrode/electrolyte interfacial chemistry, 29,40 suggest that differences in ion-solvent coordination between K + and Li + are responsible for the observed changes in SEI composition and thickness, and may ultimately lead to the observed alterations in Li deposition morphology. Our findings suggest that tuning cation identity in the electrolyte salt may be a new route to optimize electrolyte formulations for rechargeable Li metal anodes.…”

Leveraging Cation Identity to Engineer Solid Electrolyte Interphases for Rechargeable Lithium Metal Anodes

“…2,11,[18][19][20] Widely used strategies to control the composition and thickness of the SEI include tailoring the anion of the Li salt, 21 increasing the concentration of the electrolyte, [22][23][24][25][26] and using sacrificial organic electrolyte additives. [27][28][29] These strategies lead to increased amounts of LiF, cross-linking polymeric species, and polyene moieties in the SEI that are correlated with improved battery performance. 12,27,[30][31][32][33][34] Conversely, the ramifications of altering cation identity are more complicated, as the cation (e.g.…”

“…When examined with energy dispersive X-ray spectroscopy (EDS) and atomic absorption spectroscopy (AAS), we find that K + does not participate in electrochemical reaction. Rather, density functional theory (DFT) calculations, which are widely applied to study electrode/electrolyte interfacial chemistry, 29,40 suggest that differences in ion-solvent coordination between K + and Li + are responsible for the observed changes in SEI composition and thickness, and may ultimately lead to the observed alterations in Li deposition morphology. Our findings suggest that tuning cation identity in the electrolyte salt may be a new route to optimize electrolyte formulations for rechargeable Li metal anodes.…”