Niyousha Karimia,b, Maider Zarrabeitiaa,b, Hugh Geaneyc, Kevin M. Ryanc, Boyan Ilievd, Thomas J. S. Schubertd, Alberto Varzia,b and Stefano Passerinia,b
aHelmholtz Institute Ulm (HIU), Helmholtzstrasse 11, 89081, Ulm, Germany
bKarlsruhe Institute of Technology (KIT), P.O. Box 3640, 76021, Karlsruhe, Germany
cDepartment of Chemical Sciences and Bernal Institute, University of Limerick, Limerick, V94 T9PX, Ireland
dIoLiTec-Ionic Liquids Technologies GmbH, Im Zukunftspark 9, 74076, Heilbronn, Germany
Corresponding Authors: email@example.com (A. Varzi), firstname.lastname@example.org (S. Passerini)
Received 4 July 2022; Received in revised form 22 December 2022; Accepted 28 December 2022
Link to Paper:
• Cyano-based Ionic liquid (IL) electrolytes are studied with Si nanowire anodes.
• Vinylene carbonate (VC) is investigated as SEI forming additive.
• VC helps reducing IL decomposition and controlling SEI growth.
• The resulting SEI has a layered structure including inorganic and organic species.
• Si nanowire anodes deliver in such F-free electrolyte 1500 mAh g−1 after 500 cycles.
Herein, the mixture of the fluorine-free cyano-based ionic liquid N-butyl-N-methylpyrrolidinium tricyanomethanide (Pyr14TCM), lithium dicyanamide (LiDCA) (1:9 salt:IL mole ratio) and 5 wt% vinylene carbonate (VC) is proposed as an electrolyte for the stable electrochemical alloying of silicon nanowire (Si NW) anodes. Detailed electrochemical characterization of the electrolyte (long-term galvanostatic cycling and impedance tests of Si NW-Li half-cells) demonstrates a remarkable cycling performance of the Si anode delivering 1500 mAhg−1 after 500 cycles with 99.5% Coulombic efficiency. The electrode/electrolyte interface is thoroughly investigated via scanning electron microscopy (SEM), energy dispersive X-ray (EDX) mapping, and X-ray photoelectron spectroscopy (XPS). The postmortem analysis reveals the key role of VC in controlling the IL decomposition, resulting in a bilayer solid electrolyte interphase (SEI) formation. The inner layer is mostly composed of graphitic carbon serving as a conductive coating for Si, and inorganic compounds such as Li3N providing high Li-ion conductivity. The outer-layer, is rich in polymeric species ensuring the good mechanical stability and flexibility to withstand the extreme volume change of Si during de-/alloying process, thus explaining the observed prolonged cycling performance.
Keywords: Silicon anode, Fluorine-free, Ionic-liquid electrolyte, Vinylene carbonate (VC), Solid electrolyte interphase, Lithium batteries