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Nonfluorinated Ionic Liquid Electrolytes for Lithium Metal Batteries: Ionic Conduction, Electrochemistry, and Interphase Formation
Author(s) -
Karimi Niyousha,
Zarrabeitia Maider,
Mariani Alessandro,
Gatti Daniele,
Varzi Alberto,
Passerini Stefano
Publication year - 2021
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.202003521
Subject(s) - electrochemical window , ionic liquid , materials science , electrolyte , dicyanamide , ionic conductivity , electrochemistry , x ray photoelectron spectroscopy , lithium (medication) , conductivity , dielectric spectroscopy , chemical engineering , inorganic chemistry , electrode , chemistry , organic chemistry , medicine , engineering , endocrinology , catalysis
Cyano‐based ionic liquids (ILs) are prime candidates for the manufacturing of cheaper and safer batteries due to their inherently low‐volatility and absence of expensive fluorinated species. In this work, N ‐methyl‐ N ‐butylpyrrolidinium (Pyr 14 )‐based ILs featuring two different cyano‐based anions, i.e., dicyanamide (DCA) and tricyanomethanide (TCM), and their mixture with the respective Li salts (1:9 salt:IL mole ratio), alongside their combination (DCA–TCM), are evaluated as potential electrolytes for lithium metal batteries (LMBs). The electrolytes display significant ionic conductivity at room temperature (5 mS cm −1 ) alongside an electrochemical stability window up to 4 V, suitable for low‐voltage LMBs such as Li–sulfur, as well as promising cycling stability. In addition to the detailed physicochemical (viscosity, conductivity) and electrochemical (electrochemical stability window, stripping/plating, and impedance test in symmetrical Li cells) characterization, the solid electrolyte interphase (SEI) formed in this class of ionic liquids is studied for the first time. X‐ray photoelectron spectroscopy (XPS) provides evidence for an SEI dominated by a polymer‐rich layer including carbon–nitrogen single, double, and triple bonds, which provides high ionic conductivity and mechanical stability, leading to the aforementioned cycling stability. Finally, a molecular insight is achieved by density functional theory (DFT) and classic molecular dynamics simulations both supporting the experimental evidence.