The influence of FEC on the solvation structure and reduction reaction of LiPF6/EC electrolytes and its implication for solid electrolyte interphase formation

Tingzheng Hou, Guang Yang, Nav Nidhi Rajput, Julian Self, Sang Won Park, Jagjit Nanda, Kristin A. Persson

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293 Scopus citations

Abstract

Fluoroethylene carbonate (FEC) has been proposed as an effective electrolyte additive that enhances the stability and elasticity of the solid electrolyte interphase (SEI) of emerging Si and Li metal anodes. However, uncertainties still remain on the exact mechanism through which FEC alters the electrolyte decomposition and SEI formation process. Herein, the influence of FEC on LiPF6/ethylene carbonate (EC) electrolytes for Si anodes is investigated through classical molecular dynamics, Fourier-transform infrared spectroscopy, and quantum chemical calculations. Albeit a minority species, FEC is found to significantly modify the solvation structure and reduction behavior of the electrolyte while being innocuous to transport properties. Even with limited 10% of FEC, the Li+ solvation structure exhibits a notably higher contact-ion pair ratio (14%) than the parent EC electrolyte (6%). Moreover, FEC itself, as a new fluorine-containing species, appears in 1/5 of the Li+ solvation shells. The Li+-coordinated FEC is found to reduce prior to EC and uncoordinated FEC which will passivate the anode surface at an early onset (ca. 0.3 V higher than EC) by forming LiF. The critical role of FEC in tailoring the Li+ solvation structure and as-formed protective SEI composition provides mechanistic insight that will aid in the rational design of novel electrolytes.

Original languageEnglish
Article number103881
JournalNano Energy
Volume64
DOIs
StatePublished - Oct 2019

Funding

This research is supported by the U.S. Department of Energy's Vehicle Technologies Office under the Silicon Electrolyte Interface Stabilization (SEISta) Consortium directed by Brian Cunningham and managed by Anthony Burrell. This research used resources of the National Energy Research Scientific Computing Center (NERSC) , a U.S. Department of Energy Office of Science User Facility operated under Contract No. DE-AC02-05CH11231 . A portion of the research was performed using computational resources sponsored by the Department of Energy's Office of Energy Efficiency and Renewable Energy and located at the National Renewable Energy Laboratory. This research is supported by the U.S. Department of Energy's Vehicle Technologies Office under the Silicon Electrolyte Interface Stabilization (SEISta) Consortium directed by Brian Cunningham and managed by Anthony Burrell. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under Contract No. DE-AC02-05CH11231. A portion of the research was performed using computational resources sponsored by the Department of Energy's Office of Energy Efficiency and Renewable Energy and located at the National Renewable Energy Laboratory.

Keywords

  • Fluoroethylene carbonates
  • Lithium metal anodes
  • Reduction potential
  • Silicon anodes
  • Solid electrolyte interphases
  • Solvation structure

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