Effect of Water Concentration in LiPF6-Based Electrolytes on the Formation, Evolution, and Properties of the Solid Electrolyte Interphase on Si Anodes

Yeyoung Ha, Caleb Stetson, Steven Harvey, Glenn Teeter, Bertrand Tremolet de Villers, Chun-Sheng Jiang, Manuel Schnabel, Paul Stradins, Anthony Burrell, Sang Don Han

Research output: Contribution to journalArticlepeer-review

28 Scopus Citations

Abstract

A trace amount of water in an electrolyte is one of the factors detrimental to the electrochemical performance of silicon (Si)-based lithium-ion batteries that adversely affect the formation and evolution of the solid electrolyte interphase (SEI) on Si-based anodes and change its properties. Thus far, a lack of fundamental and mechanistic understanding of SEI formation, evolution, and properties in the presence of water has inhibited efforts to stabilize the SEI for improved electrochemical performance. Thus, we investigated the SEI formed in a Gen2 electrolyte (1.2 M LiPF6 in ethylene carbonate/ethyl methyl carbonate, 3:7 wt %, water content: <10 ppm) with and without additional water (50 ppm) at varying potentials (1.0, 0.5, 0.2, and 0.01 V vs Li/Li+). The impact of additional water on the morphological, (electro)chemical, and structural properties of SEI was studied using microscopic (atomic force microscopy and scanning spreading resistance microscopy) and spectroscopic (X-ray photoelectron spectroscopy, attenuated total reflection Fourier-transform infrared spectroscopy, and time-of-flight secondary ion mass spectrometry) techniques. The SEI exhibits both potential- and water concentration-dependent trends in its morphology and chemical composition. The presence of additional water in the electrolyte causes parasitic reactions, which onset at ∼1.0 V, resulting in a reduction of electrolyte components and result in the formation of an insulating, fluorophosphate-rich SEI. In addition, hydrolysis of LiPF6 creates hydrofluoric acid, which reacts with the surface oxide layer on the Si electrode, leading to a pitted and inhomogeneous SEI structure.

Original languageAmerican English
Pages (from-to)49563-49573
Number of pages11
JournalACS Applied Materials and Interfaces
Volume12
Issue number44
DOIs
StatePublished - 4 Nov 2020

Bibliographical note

Publisher Copyright:
© 2020 American Chemical Society.

NREL Publication Number

  • NREL/JA-5900-77016

Keywords

  • electrolyte water concentration
  • fluorophosphates
  • hydrolysis of LiPF
  • Si anode
  • solid electrolyte interphase
  • surface pitting

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